United States Patent ( 10 ) Patent No.: US 10,495,601 B2 Abdulazeez Et Al

US010495601B2

United States Patent ( 10 ) Patent No.: US 10,495,601 B2 Abdulazeez et al. (45 ) Date of Patent: Dec. 3 , 2019

(54 ) RARE EARTH METAL INCORPORATED (58 ) Field of Classification Search ZEOLITE MODIFIED ELECTRODES FOR CPC GO1N 27/333 ; GOIN 27/308 ; GOIN 27/48 ; DETECTION AND QUANTIFICATION OF GOIN 27/3277 HEAVY METAL IONS IN AQUEOUS See application file for complete search history . SOLUTION ( 71 ) Applicant: KING FAHD UNIVERSITY OF (56 ) References Cited PETROLEUM AND MINERALS , Dhahran (SA ) FOREIGN PATENT DOCUMENTS CN 100570349 C 12/2009 (72 ) Inventors : Ismail Abdulazeez, Dhahran (SA ); CN 103713036 A 4/2014 Abdel -Naser M. Kawde , Dhahran 104020213 A 9/2014 (SA ); Oki Muraza , Dhahran (SA ); GB 1 262 019 2/1972 Abdul- Rahman Al- Betar , Dhahran (SA ) OTHER PUBLICATIONS (73 ) Assignee : King Fahd University of Petroleum A. Walcarius, et al . “ Zeolite -modified solid carbon paste electrode” , and Minerals , Dhahran (SA ) Journal of Solid State Electrochemistry , 7 ( 10 ) :p . 671-677, Oct. 2003. * ( * ) Notice : Subject to any disclaimer, the term of this E.F. Sousa - Aguiar, et al . “ The role of rare earth elements in zeolites patent is extended or adjusted under 35 and cracking catalysts ” , Catalysis Today, v . 218-219 , p . 115-127 , U.S.C. 154 (b ) by 387 days . Dec. 2013. * (21 ) Appl. No .: 15 /446,035 (Continued ) ( 22 ) Filed : Mar. 1 , 2017 Primary Examiner — J. Christopher Ball (74 ) Attorney, Agent, or Firm — Oblon ,McClelland , (65 ) Prior Publication Data Maier & Neustadt, L.L.P. US 2017/0315079 A1 Nov. 2 , 2017 Related U.S. Application Data (57 ) ABSTRACT Electrodes comprising conducting graphite , paraffin oil past (60 ) Provisional application No.62 /330,627 , filed on May ing liquid , and a rare earth metal impregnated zeolite , such 2 , 2016 . as lanthanum or cerium impregnated mordenite electrodes . (51 ) Int. Ci. Methods and voltammetric applications, such as square GOIN 27/333 ( 2006.01 ) wave anodic stripping voltammetry , of these rare earth metal GOIN 27/48 ( 2006.01) impregnated zeolite modified electrodes for the detection GOIN 27/30 ( 2006.01 ) and quantification of heavy metal ions such as Pb ( II ) and ( 52 ) U.S. CI. Cd ( II ) in aqueous solutions. CPC GOIN 27/333 ( 2013.01 ) ; GOIN 27/308 ( 2013.01 ); GOIN 27/48 (2013.01 ) 20 Claims, 76 Drawing Sheets

DEL US 10,495,601 B2 Page 2

( 56 ) References Cited Linyuan Cao , et al . “ Sensitive determination of Cd and Pb by differential pulse stripping voltammetry with in situ bismuth modified zeolite doped carbon paste electrodes” , Electrochimica OTHER PUBLICATIONS Acta , vol . 53 , 2008 , pp . 2177-2182 . Beatriz O. Hincapie , et al ., “ Synthesis of mordenite nanocrystals ” , Microporous and Mesoporous Materials , vol. 67 , 2004 , pp . 19-26 . A. Nezamaedeh - Ejhieh , et al. (“ Voltammetric determination of Hisham M. Aly , et al. , “ Synthesis of mordenite zeolite absence of riboflavin based on electrocatalytic oxidation at zeolite -modified organic template ” , Advanced Powder Technology , vol. 23 , 2012, pp . carbon paste electrodes ” , Journal of Industrial and Engineering 757-760 . Chemistry , 20 ( 4 ) : p . 2146-2152, Jul. 2014.* Georgia Kefala , et al. , “ Polymer- coated bismuth film electrodes for M. Arvand , et al. “ Electrochemical study of atenolol at a carbon the determination of trace metals by sequential- injection analysis / paste electrode modified with mordenite type zeolite ” , Material anodic stripping voltammetry” , Analytica Chimica Acta , vol. 576 , Science and Engineering C , 30 ( 5 ) : p . 709-714 , Jun . 2010.* 2006 , pp . 283-289. A.A. Shaikh, et al. “ Direct hydrothermal crystallization of high Gyoung - Ja Lee , et al ., “ Bismuth nano - powder electrode for trace silica large- port mordenite ” , Zeolites 13 ( 7 ) : Abstract only , Sep. analysis of heavy metals using anodic stripping voltammetry" , 1993.* Electrochemistry Communications, vol. 9 , 2007, pp . 2514-2518 . A. Ismail , et al. , “ Lanthanum -impregnated zeolite modified carbon Watsaka Siriangkhawut, et al. , “ Sequential injection monosegmented paste electrode for determination of Cadmium ( II ) " , Microporous flow voltammetric determination of cadmium and lead using a and Mesoporous Materials , vol. 225, 2016 , pp . 164-173 . bismuth film working electrode ” , Talanta, vol. 79, 2009, pp . 1118 S. Senthilkumar, et al ., “ Electrochemical sensing of cadmium and 1124 . lead ions at zeolite -modified electrodes : Optimization and field measurements ” , Sensors and Actuators B , vol. 141, 2009, pp .65-75 . * cited by examiner U.S. Patent Dec. 3 , 2019 Sheet 1 of 76 US 10,495,601 B2

more ( +- ) Enc

?? ,?

RO more ( - ) Epa more ( + ) potential more (- )

FIG . 1 U.S. Patent Dec. 3 , 2019 Sheet 2 of 76 US 10,495,601 B2

E To Potential (V ) vs. Ag/ Aga

FIG . 2 U.S. Patent Dec. 3 , 2019 Sheet 3 of 76 US 10,495,601 B2

Sample period

Step AE

potential Pulse period

FIG . 3 U.S. Patent Dec. 3 , 2019 Sheet 4 of 76 US 10,495,601 B2

Sample period

Pulse amplitude

Quiet time

FIG . 4 U.S. Patent Dec. 3 , 2019 Sheet 5 of 76 US 10,495,601 B2

Sample Potential period

Amplitude (E ) AE U.S. Patent Dec. 3 , 2019 Sheet 6 of 76 US 10,495,601 B2

(E- ) (mv )

FIG . 6 U.S. Patent Dec. 3 , 2019 Sheet 7 of 76 US 10,495,601 B2

Oooola

FIG.7 U.S. Patent Dec. 3 , 2019 Sheet 8 of 76 US 10,495,601 B2

FIG . 8 U.S. Patent Dec. 3 , 2019 Sheet 9 of 76 US 10,495,601 B2

Zeolite modified carbon paste U.S. Patent Dec. 3 ,? 2019 Sheet 10 of 76 US 10,495,601 B2

Analcime

???????????????????? ????

poos Intensity(a.u.) hemembantulah ???? harmant Luhrenheith???? ??? whenchmahan malaman ninh 20 ( degree ) U.S. Patent Dec. 3 , 2019 Sheet 11 of 76 US 10,495,601 B2 U.S. Patent Dec. 3 , 2019 Sheet 12 of 76 US 10,495,601 B2

FIG . 12 U.S. Patent Dec. 3 , 2019 Sheet 13 of 76 US 10,495,601 B2

20 ur

FIG . 13 U.S. Patent Dec. 3 , 2019 Sheet 14 of 76 US 10,495,601 B2 U.S. Patent Dec. 3 , 2019 Sheet 15 of 76 US 10,495,601 B2

6 8

FIG . 15 U.S. Patent Dec. 3 , 2019 Sheet 16 of 76 US 10,495,601 B2

WHwaran non van wherman

man ay marahmutphon 150 50 100 150 200 250 Chemical shift ( ppm )

FIG . 16 U.S. Patent Dec. 3 , 2019 Sheet 17 of 76 US 10,495,601 B2

Current(UA)

??????? ??????????????? -0.2 0.2 0.4 0.8 E / V vs Ag/ AgCl U.S. Patent Dec. 3 , 2019 Sheet 18 of 76 US 10,495,601 B2

30 di)vm(

20 30 La -MOR - 15 % U.S. Patent Dec. 3 , 2019 Sheet 19 of 76 US 10,495,601 B2

Current(LLA)

400

-10

E / V vs Ag/ Age FIG . 19 U.S. Patent Dec. 3 , 2019 Sheet 20 of 76 US 10,495,601 B2

y = 1.73871 +4.0127 R2 = 0.9992 Current(UA) 20

0 2 8 18 20 (Scan rate ) 12 FIG . 20 U.S. Patent Dec. 3 , 2019 Sheet 21 of 76 US 10,495,601 B2

Current(UA)

0.2

FIG . 21 U.S. Patent Dec. 3 , 2019 Sheet 22 of 76 US 10,495,601 B2

yo 2.948x * 7.8081

FIG . 22 U.S. Patent Dec. 3 , 2019 Sheet 23 of 76 US 10,495,601 B2

140

120 -

100

Current(UA) 60

20 -

-0.6 -0.2 E / V vs Ag /AgCI

FIG . 23 U.S. Patent Dec. 3 , 2019 Sheet 24 of 76 US 10,495,601 B2

1.3

FIG . 24 U.S. Patent Dec. 3 , 2019 Sheet 25 of 76 US 10,495,601 B2

140

120

100 1 Current(UA)

-1.2 -0.8 -0.2 0.0 E / V vs Ag/ AgCI

FIG . 25 U.S. Patent Dec. 3 , 2019 Sheet 26 of 76 US 10,495,601 B2

Current(1) 90 ***************************

20 170 Accomulation time is

FIG . 26 U.S. Patent Dec. 3 , 2019 Sheet 27 of 76 US 10,495,601 B2

Current(PA)

50 ppb

EIV vs AgAgci

FIG . 27 U.S. Patent Dec. 3 , 2019 Sheet 28 of 76 US 10,495,601 B2

Current(MA)

E /Vvs Ag/ AgCI

FIG . 28 U.S. Patent Dec. 3 , 2019 Sheet 29 of 76 US 10,495,601 B2

y = 0.11631-3.0945

0 [C ( IT ) ppb

FIG . 29

35 y = 0.0545x + 0.3453 3 2.5

15 good

0 CA (IT ) ppb

FIG . 30 U.S. Patent Dec. 3 , 2019 Sheet 30 of 76 US 10,495,601 B2

Current(MA)

EIVvs AgAga

FIG . 31 U.S. Patent Dec. 3 ,? 2019 Sheet 31 of 76 US 10,495,601 B2

{b } Intensity(a.u.) whenhalle????? whethman

{ } ??????? 5 Ander3 {} 20 ( degree )

FFG.32 U.S. Patent Dec. 3 , 2019 Sheet 32 of 76 US 10,495,601 B2

MOR - 15

FIG . 33 U.S. Patent Dec. 3 , 2019 Sheet 33 of 76 US 10,495,601 B2

0 U.S. Patent Dec. 3 ,? 2019 Sheet 34 of 76 US 10,495,601 B2

{ }} ?????hahah dulu ????? ????? heruntMandramanmarathon nhanh ??????? homembenanthi mathemahan a ) ???????????? ?????? ????25 35 20 ( degree )

FIG , 35 U.S. Patent Dec. 3 ,? 2019 Sheet 35 of 76 US 10,495,601 B2

haha Intensity(a.u) ????? ???????????halaman Laulman hrada anaand ?????????????? 5 1 2 20 ( degree )

1.36 U.S. Patent Dec. 3 , 2019 Sheet 36 of 76 US 10,495,601 B2

FIG . 37 U.S. Patent Dec. 3 , 2019 Sheet 37 of 76 US 10,495,601 B2

FIG . 38 U.S. Patent Dec. 3 , 2019 Sheet 38 of 76 US 10,495,601 B2

FIG . 39 U.S. Patent Dec. 3 , 2019 Sheet 39 of 76 US 10,495,601 B2 U.S. Patent Dec. 3 , 2019 Sheet 40 of 76 US 10,495,601 B2 U.S. Patent Dec. 3 , 2019 Sheet 41 of 76 US 10,495,601 B2

FIG . 42 U.S. Patent Dec. 3 , 2019 Sheet 42 of 76 US 10,495,601 B2

d )

( b )

(a )

150 Chemical shift ( ppm ) FIG . 43 U.S. Patent Dec. 3 , 2019 Sheet 43 of 76 US 10,495,601 B2

Current(MA) 10

EIVvs Ag/ AgCI

FIG . 44 U.S. Patent Dec. 3 , 2019 Sheet 44 of 76 US 10,495,601 B2

Current(A)

8 Percent La loading (wt % ) U.S. Patent Dec. 3 , 2019 Sheet 45 of 76 US 10,495,601 B2

Qurrant() a

-0.2 EIV vs Ag /Agci FIG . 46 U.S. Patent Dec. 3 , 2019 Sheet 46 of 76 US 10,495,601 B2

14 freesome 12 Current(A) 8 6

4 6 Percent Ce loading (wt % ) U.S. Patent Dec. 3 , 2019 Sheet 47 of 76 US 10,495,601 B2

12 25

20 Current(UA)

0.0 ETV vs Ag/ AgCI

FIG . 48 U.S. Patent Dec. 3 , 2019 Sheet 48 of 76 US 10,495,601 B2

umo)W(

EIV vs Ag/ AgCi U.S. Patent Dec. 3 , 2019 Sheet 49 of 76 US 10,495,601 B2

Current(UA) S

0 Composite electrodesm

Current(UA) 5 E

F 2000 Composite electrodes

FIG . 51 U.S. Patent Dec. 3 , 2019 Sheet 50 of 76 US 10,495,601 B2

a 20 (b )

1.2 E / Vvs Ag/ AgCI U.S. Patent Dec. 3 , 2019 Sheet 51 of 76 US 10,495,601 B2

Current(UA) 15

5 Acetate 11Phosphate Sulphate 0.1 M buffer solutions (pH 4 )

FIG . 53 U.S. Patent Dec. 3 , 2019 Sheet 52 of 76 US 10,495,601 B2

( a )

(b )

(0 ) 5

0.0 E /Vvs Ag/ AgCI U.S. Patent Dec. 3 , 2019 Sheet 53 of 76 US 10,495,601 B2

Current(UA) 15

Phosphate Sulphat 0.1 M buffer solutions (pH 4 ) U.S. Patent Dec. 3 , 2019 Sheet 54 of 76 US 10,495,601 B2

20 CurrentNA()

5 6

« 1.0 E / V vs Ag/ AgCI

FIG . 56 U.S. Patent Dec. 3 , 2019 Sheet 55 of 76 US 10,495,601 B2

Current(UA) 15

2 3 5 6 7 8 pH U.S. Patent Dec. 3 , 2019 Sheet 56 of 76 US 10,495,601 B2

Current(UA)

-0.2 E / V vs Ag/ AgCI

FIG . 58 U.S. Patent Dec. 3 , 2019 Sheet 57 of 76 US 10,495,601 B2

Current(UA)

2 3 an 8 pH

25 Current(UA) 15

Amplitude ( V )

FIG . 60 U.S. Patent Dec. 3 , 2019 Sheet 58 of 76 US 10,495,601 B2

Current(UA)

Amplitude (V )

FIG . 61

Current(UA) 90

120 180 Frequency (Hz )

FIG . 62 U.S. Patent Dec. 3 , 2019 Sheet 59 of 76 US 10,495,601 B2

310

210 Current(UA)

110

120 140 Frequency (Hz )

FIG . 63

Current(UA) 1

0 0.5 Accumulation E / V

FIG . 64 U.S. Patent Dec. 3 , 2019 Sheet 60 of 76 US 10,495,601 B2

25 Current(UA) 20

-1.6 -1.4 -1.2 -1 Accumulation E / V U.S. Patent Dec. 3 , 2019 Sheet 61 of 76 US 10,495,601 B2

180

120

Current(HA)1,600 100 poput 180 sec supra****************************** Prinssin *************************************************pembipop phpM ************** ******** 20 sec *** ***************** ******************* inguesh :

EIV vs Ag /AgCI FIG . 66 U.S. Patent Dec. 3 , 2019 Sheet 62 of 76 US 10,495,601 B2

Current(1) ww444444BBAME*** BARVA

*** U.S. Patent Dec. 3 , 2019 Sheet 63 of 76 US 10,495,601 B2

120

100

80 Current(HA)

20 sec

0 E /Vvs Ag/ AGCI FIG . 68 U.S. Patent Dec. 3 , 2019 Sheet 64 of 76 US 10,495,601 B2

30 Accumulation Time (sees ) U.S. Patent Dec. 3 , 2019 Sheet 65 of 76 US 10,495,601 B2

Current(HA)

E / V vs Ag /AgCI

FIG . 70 U.S. Patent Dec. 3 , 2019 Sheet 66 of 76 US 10,495,601 B2 U.S. Patent Dec. 3 , 2019 Sheet 67 of 76 US 10,495,601 B2

50 ppb Current(PA) !

5 5 ppb

***

E / V vs Ag/ AgCI

FIG . 72 U.S. Patent Dec. 3 , 2019 Sheet 68 of 76 US 10,495,601 B2

FIG . 73 U.S. Patent Dec. 3 , 2019 Sheet 69 of 76 US 10,495,601 B2

WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW

11 500 ppb

Current(MA) 50 ppb 30 w

uz -1.2 0.0 EIVvs Ag /AGCI FIG . 74 U.S. Patent Dec. 3 , 2019 Sheet 70 of 76 US 10,495,601 B2

00 U.S. Patent Dec. 3 , 2019 Sheet 71 of 76 US 10,495,601 B2

Current(HA) 50 ppb

5 pph

en EIVVS AgAgCI

FIG . 76 U.S. Patent Dec. 3 , 2019 Sheet 72 of 76 US 10,495,601 B2

95 U.S. Patent Dec. 3 , 2019 Sheet 73 of 76 US 10,495,601 B2

500 ppb Current(HA)

50 ppb

EIVvs Ag/ AgCI

FIG . 78 U.S. Patent Dec. 3 , 2019 Sheet 74 of 76 US 10,495,601 B2

100 y = 0.1785x - 3.2787 Cd ( II ) 80 R = 0.9985 Current(A) 60 Pb ( IT )

y = 0.1287x - 0.9988 R2 = 0.9978

(Cd ( II ) and Pb (ID ) ) ppb

FIG . 79 U.S. Patent Dec. 3 , 2019 Sheet 75 of 76 US 10,495,601 B2

500 ppb Current(HA)

EIV vs Ag /AgCl

FIG . 80 U.S. Patent Dec. 3 , 2019 Sheet 76 of 76 US 10,495,601 B2

50 40 y = 0.0861x - 2.6893 R = 0.9976 Current(MA) 30 Pb ( II )

. * y = 0.0717x - 2.7747 10

[Cd ( II) and Pb ( IT ) ppb

FIG . 81 US 10,495,601 B2 1 2 RARE EARTH METAL INCORPORATED entirety ]. Cadmium accumulates in the kidney, liver and ZEOLITE MODIFIED ELECTRODES FOR various other organs and is considered more harmful than DETECTION AND QUANTIFICATION OF either mercury or lead . In fact, it is harmful even at levels HEAVY METAL IONS IN AQUEOUS one tenth that ofmercury , lead , aluminum or nickel . Expo SOLUTION 5 sure to this metal is increasing today as a result of its use as a coating for steel iron and copper. Cadmium is also used in CROSS REFERENCE TO RELATED stabilizers , copper alloys , in rubber and plastics, fungicides , APPLICATIONS cigarette papers , and in many other products . Often , these industries pollute water , air and food with this metal. This application claims the benefit of priority from U.S. 10 Another frequently encountered toxic pollutant in the Provisional Application No. 62/ 330,627 filed May 2 , 2016 , the entire contents of which are herein incorporated by environment is lead as a result of its use in paints , gasoline reference . and car batteries . Lead is known for its manifestation in the form of several health problems, such as cardiac , mental and BACKGROUND OF THE INVENTION 15 neurological disorders . As many as thirty important health conditions have been linked lead , many of which affect Technical Field children and the unborn . It has also been reported that the The present disclosure relates to rare earth metal impreg function of lead in the body is unknown . Lead can substitute nated zeolite modified electrodes, such as lanthanum or 20 for calcium in bones and may delay osteoporosis ( a medical cerium impregnated mordenite electrodes. In addition , the condition which causes the bones to become weak and present disclosure relates to applications of these electrodes brittle ) . However , lead causes other metabolic problems in in voltammetric methods, such as square wave anodic strip the body, and hence calcium is the preferred element. ping voltammetry , for the detection and quantification of Symptomsof lead toxicity may appear years after exposure , heavy metal ions such as Pb ( II ) and Cd ( II) in aqueous 25 as a result of the sudden release of stored lead due to illness , solutions . alcoholism , stress or other metabolic changes . Sources of Description of the Related Art lead include paints , radioactive disintegration of uranium , car batteries , lead pipes, hair colorings, and the like. The " background " description provided herein is for the 30 Mercury is one of the members of the class of toxic metals purpose of generally presenting the context of the disclo which have been recognized since prehistoric times. It is sure . Work of the presently named inventors , to the extent it poisonous in any form , with its toxicity commonly affecting is described in this background section , as well as aspects of the neurological, gastrointestinal and renal organ systems. the description which may not otherwise qualify as prior art Poisoning from mercury can occur as a result of vapor at the time of filing , are neither expressly or impliedly 35 inhalation , injection, ingestion , and penetration through the admitted as prior art against the present invention . Heavy metals are naturally occurring elements , which are skin . It exists in three forms: elemental, organic and inor found in various concentrations in all ecosystems. Over the ganic forms. The three forms are interconvertible , and can years, human activities through technological development all produce systemic toxicity . Mercury is widely used in and industrial events have resulted in the discharge of heavy 40 industry and in a variety of products , such as fungicides , metals into the environment which has today become a algaecides used in swimming pools, in the manufacture of matter of great concern . While there is still no clear defini adhesives, floor waxes, fabric softeners, and in the produc tion of what a heavy metal is , it is sometimes referred to as tion of chlorine . any metallic element with a high relative density ( > 5 g / cm ”) Another harmful carcinogen to both humans and animals and which is toxic or fatal at even low concentrations 45 is arsenic . Its toxicity has been linked with cancers of the [ Nagajyoti , P. C., K. D. Lee , and T. V. M. Sreekanth , Heavy bladder , skin and lung . It is estimated that as many as tens metals , occurrence and toxicity for plants : a review . Envi ronmental Chemistry Letters , 2010. 8 (3 ) : p . 199-216 . of millions of people are at risk of exposure to enormous incorporated herein by reference in its entirety ] . In addition levels of arsenic as a result of exposure to contaminated to the density , it has also been established that the chemical 50 water and arsenic containing coal from natural sources [Ng , properties of the metal are an influencing factor when J. C., J. Wang, and A. Shraim , A global health problem classifying heavy metals . They include metals such as chromium , lead , cadmium , cobalt, nickel, mercury, iron , caused by arsenic from natural sources. Chemosphere , silver , arsenic , as well as the platinum group elements . The 2003. 52 ( 9 ): p . 1353-1359. — incorporated herein by refer major risks associated with heavy metals come with expo- 55 ence in its entirety ]. Chronic arsenic exposure may lead to sure to lead , cadmium , mercury and arsenic [ Järup , L., skin cancer , diabetes , black foot disease , papillary and Hazards of heavy metal contamination . British Medical Bulletin , 2003. 68 (1 ): p . 167-182 . — incorporated herein by cortical necrosis , and the like . Table 1 summarizes the reference in its entirety ]. maximum contaminant level (MSL ) allowed of some inor Cadmium is an extremely toxic metal whose toxicity 60 ganic contaminants in domestic water , their common presents a number of health issues , including major fatal sources, and their potential health effects as adapted from the diseases such as heart disease, cancer and diabetes [Shams , EPA National Primary Drinking Water Standards tables E. and R. Torabi, Determination of nanomolar concentra tions of cadmium by anodic - stripping voltammetry at a [ Patterson , K. Y. , P. R. Pehrsson , and C. R. Perry , The carbon paste electrode modified with zirconium phosphated 65 mineral content of tap water in United States households. amorphous silica . Sensors and Actuators B : Chemical, 2006 . Journal of Food Composition and Analysis , 2013. 31 ( 1 ): p . 117 ( 1) : p . 86-92 . — incorporated herein by reference in its 46-50 . — incorporated herein by reference in its entirety ]. US 10,495,601 B2 3 4 TABLE 1 before being atomized and subsequently analyzed . The advantage of GFAAS over AAS is that the limit of detection Maximum contaminant levels of inorganic chemicals allowed in drinking in GFAAS is about two orders ofmagnitude greater than that water of AAS . MCL Potential Health 5 Inductively coupled plasma- optical emission spectrom Contaminant (ppm ) Common Source Effect etry ( ICP -OES ) is among the most robust analytical tools for Arsenic (AS ) 0.01 Drainage from glass and Skin damage ; the measurement of trace elements in numerous types of electronic production prospect of getting samples . The working principle of ICP -OES relies upon the waste cancer rapid release of photons from atoms and ions that have been Barium (Ba ) 2 Release of drilling Increase in blood 10 excited in a radio frequency (RF ) discharge . One major wastes , and metal pressure refineries advantage of this technique is the fact that it can analyze Cadmium 0.005 Decay of galvanized Kidney impairment samples of any form ( solid , liquid or gaseous ). The sample ( Cd ) pipes; release from metal solution is transformed to an aerosol and sent into the central refineries, drainage from channel of the plasma. At its core the plasma sustains a waste batteries and paints Chromium 0.1 Release from steel and Allergic dermatitis 15 temperature of approximately 10,000 K , such that the aero (Cr ) pulp mills sol is quickly vaporized . Analyte elements are released as Lead ( Pb ) 0.015 Decay of household Kidney diseases and free atoms in the gaseous state . An ample amount of energy plumbing systems high blood pressure is often available to transform the atoms to ions and later to in adults Mercury 0.002 Release from refineries Kidney damage promote the ions to excited states. Bothe the atomic and (Hg ) and factories 20 ionic excited state species may then return to the ground inorganic ) state with the emission of a photon . These photons possess Selenium 0.005 Release from petroleum Hair or fingernail characteristic energies that are determined by the quantized (Se ) and metal refineries loss , circulatory problems energy level structure for the atoms or ions. Hence , the Thallium 0.002 Seep from ore Loss of hair, kidney, wavelength of the photons can be used to identify the ( TI) processing sites, release intestine or liver 25 elements from which they were emitted . The total number of from electronics , glass , complications emitted photons is directly proportional to the concentration and drug factories CN 0.2 Release from steel Nerve damage or of the element in the sample . (as free factories, discharge from thyroid One major disadvantage of the optical techniques dis cyanide ) plastic and fertilizer complications cussed herein is that they require highly sophisticated instru factories 30 mentation , and are not suitable for on - site monitoring . Fluoride ( F ) 4.0 Water supplement which Bone infections (pain Alternatively, electroanalytical techniques offer a simple enhances strong teeth and tenderness of approach with several advantages , such as rapid analysis , bones ) portability , good selectivity and sensitivity . Voltammetric techniques, and stripping techniques in particular are well Several methods exist for the detection of heavy metals . 35 suited for the determination of trace amounts of heavy Optical methods include spectroscopic techniques such as atomic absorption spectrometry (AAS ) , graphite furnace metals due to their speed , remarkable analytical sensitivity , atomic absorption spectrometry (GFAAS ) , inductively simplicity , low cost , and minimum sample pre - treatment coupled plasma- optical emission spectrometry ( ICP -OES ) , [Prabakar , S. J. R., C. Sakthivel, and S. S. Narayanan , Hg( II ) inductively coupled plasma- mass spectrometry ( ICP -MS ) 40 immobilizedstripping voltammetric MWCNT determinationgraphite electrode of lead for and the cadmium anodic . and the like . Talanta , 2011. 85 ( 1 ): p . 290-297 . — incorporated herein by Atomic absorption spectrometry (AAS ) is a common reference in its entirety ]. Electroanalytical techniques are spectroscopic technique for the qualitative determination of among the most powerful and popular techniques used in chemical elements using the absorption of optical radiation analytical chemistry . The techniques offer a remarkable by free atoms in the gaseous state . The atoms absorb 45 sensitivity , accuracy , and precision in addition to a large ultraviolet or visible light and make transitions to higher linear dynamic range , with relatively low cost instrumenta energy levels . A detector measures the wavelengths of light tion . The electroanalytical techniques have found applica transmitted by the sample , and compares them to the wave length which originally passed through the sample . A signal tions in areas such as environmental studies, industrial processor then integrates the change in wavelength 50 techniquesquality control such, biomedical as ; cyclic analysisvoltammetry , and so(CV on ) ,. linearThey include sweep absorbed , which appear in the read -out as peaks of energy voltammetry (LSV ) , normal pulse voltammetry (NPV ) , dif absorption at discrete wavelengths. All atoms have their ferential pulse voltammetry (DPV ) , square wave voltamme distinct pattern of wavelengths at which they will absorb try (SWV ) , anodic stripping voltammetry (ASV ) , cathodic energy , due to the unique configuration of electrons in their stripping voltammetry (CSV ), and the like . outer shells . The concentration of the analyte is then calcu 55 Cyclic voltammetry (CV ) is an electrochemical technique lated based on the Beer - Lambert law as given by the where the potential at a working electrode is changed equation of formula ( I ) . linearly with time while measuring the resulting current. This gives rise to voltammograms which provide informa A = bc ( I) : tion about the reactivity and mass transport properties of an In this equation , A is absorbance, E is a molar absorptivity 60 electrolyte . CV is one of the most widely used electroana coefficient, b is the path length , and C is the concentration . lytical methods because of its ability to study and charac Graphite furnace atomic absorption spectrometry terize redox systems from macroscopic scales down to (GFAAS ) is a technique that possesses the same working nanoelectrodes as well as composite electrodes. An exem principle as AAS. The difference between the two is the way plary typical CV voltammogram is shown in FIG . 1 [ Ivaska , in which the sample is injected into the instrument. In 65 A. and J. Bobacka , PROCESS ANALYSIS |Electroanalytical GFAAS , an electrothermal graphite furnace is used . The Techniques , in Encyclopedia of Analytical Science (Second sample is heated gradually ( up to 3000 ° C.) until it dries Edition ), P. W. T. Poole , Editor. 2005 , Elsevier: Oxford . p . US 10,495,601 B2 5 6 309-316 . — incorporated herein by reference in its entirety ] . In this equation , tm is the time after application of the pulse In FIG . 1 Ep.e and Ep, a are the peak potential at the cathode where the current is measured . An exemplary typical signal and anode , respectively , and ip ,e and ip ,a are the peak currents for normal pulse voltammetry is shown in FIG . 3 . at the cathode and anode , respectively . The peak current in Differential pulse voltammetry (DPV ) is a very useful CV is given by the Randles- Sevcik equation of formula ( II) . 5 technique for detecting trace amounts of organic and inor ganic species. In DPV , fixed magnitude pulses superimposed ip =( 2.69x105 ) n3 / 2AD1 / 2,1 / 20 ( II ) : on a linear potential ramp are applied to the working In this equation , n is the number of electrons in the redox electrode just before the end of the drop (FIG . 4 ) . The system , A is the area of the working electrode , D is the current is measured twice, before the pulse application and diffusion coefficientof the electroactive species, v is the scan 10 after the pulse (after -40 ms, when the charging current goes rate and C is the concentration of the electroactive specie at down ). The first current is instrumentally deducted from the the electrode . second , and this current difference is graphed against the Cyclic voltammetry provides qualitative information applied potential . The resulting differential pulse voltammo about electrochemical processes under different conditions, 15 gram consists of current peaks , whose height is directly which include the presence of intermediates in redox reac proportional to the concentration of the corresponding ana tions and the reversibility of a reaction . It is also used to lyte . The peak potential (Ey ) appears close to the polaro determine the electron stoichiometry of a system , the diffu graphic half wave potential and can be used to identify the sion coefficient of an analyte , and the formal reduction species . This technique is useful for analyzing mixtures with potentialAdditionally, which, because can concentrationbe used as anis proportionalidentification to toolcur-. 20 very low detection limits . It is also used to yield information rent in a reversible , Nernstian system , concentration of an about the chemical nature of the analyte . unidentified solution can be found by generating a calibra Square wave voltammetry (SWV ) is a robust electro tion curve of current versus concentration . chemical technique suitable for analytical applications , In linear sweep voltammetry (LSV ) , potential is varied at mechanistic studies of electrode processes and electrokinetic a constant rate while the current is measured . The rate of 25 measurements [Mirceski , V., et al. , Square - Wave Voltam change of the potential is called the scan rate ( v ). Tradition mety : A Review on the Recent Progress . Electroanalysis , ally , the potential is plotted on the x - axis with more negative 2013. 25 ( 11) : p . 2411-2422 . — incorporated herein by refer ( i.e. reducing ) potentials to the right . Currents , in contrast , ence in its entirety ]. In this technique, current is measured are graphed on the y - axis with currents due to reduction twice during each square wave cycle , once at the completion assigned positive values . In LSV, it is common practice to 30 of the forward pulse , and once at the completion of the measure the peak current (ip ), the largest current; peak reverse pulse . Because the square wave modulation ampli potential (Ep ) , the potential at the peak current and the tude is very large , the reverse pulse leads to the reverse half -peak potential ( E12) , which is the potential when the reaction of the product (of the forward pulse ). Thus, the current is half of the peak current. The potential at the peak difference between the two measurements is graphed versus is characteristic of the system being investigated . It is mainly 35 the base staircase potential. This is shown in FIG . 5. A plot a thermodynamic measurement, but may be affected by the kinetics of the system . The value of the peak current depends of the theoretical forward , reverse and difference currents is on several factors including the analyte concentration , kinet given in FIG . 6 for a reversible redox system . The resulting ics of electron transfer and the mass transport of the analyte . peak shaped voltammogram is symmetric about the half FIG . 2 shows and exemplary typical LSV voltammogram of 40 waveconcentration potential . , The and major the peak advantage current of is thisproportional technique to over the ferrocene. In a diffusion controlled system , with reversible other electrochemical techniques is its speed , sensitivity , and electron transfer, the relationship is given by an equation of the fact that it can reach very low limits of detection . formula (III ) . Anodic stripping voltammetry (ASV ) is one of the most 45 common of a class of techniques known as stripping elec ip = ( 2.69x10 )n3 / 2AD1 / 2,1 / 2C * ( III) : toranalytical methods. The distinguishing property of this In this equation , C * is the bulk concentration of analyte (mol technique is the deposition of analyte at the surface of the analyte / cm ° ) and all other variables and symbols are the electrode , and thus a lowered detection limit for the analyte . same as in the Randles -Sevcik equation . The dependence on ASV involves the deposition of electroactive species at the bulk concentration ( rather than concentration at the elec- 50 electrode surface by the application of a negative potential . trode surface ( allows peak current to be used for quantitative In most cases a mercury drop electrode ormercury thin film purposes. Normal pulse voltammetry (NPV ) consists of stages of electrode is used under forced convective conditions (i.e. pulses of rising amplitude applied to successive drops at a stirred solution ). The deposition step is followed by a short preselected tem close to the end of each drop lifetime, while 55 stirringtime period) , after in whichwhich thea potential solution isscan allowed is initiated to quiet from (i.e. the no the electrode is maintained at a base potential between deposition potential in the anodic direction . From the result pulses where no reaction occurs . Current is measured at ing voltammogram , the current magnitude (peak height) or around 40 ms after each pulse is applied and is graphed as a function of the potential . The resulting voltammogram has charge (peak area ) is then used to quantify unknown a sigmoidal shape, with a limiting current represented by a 60 amountssurface ofof an analyte inert .substrate For a mercury , the stripping film deposited peak current on the is modified Cottrell equation of formula ( IV ) . given by an equation of formula ( V ) .

nFACD1/ 2 (IV ) n - F2,1/ 2 AICM ( V ) ???? 65 2.7RT US 10,495,601 B2 7 8 In this equation , F represents the Faraday ( 9.65x104 C ), I is scan . This yields the advantage of self -renewal , so it does themercury film thickness in cm , and all other variables and not need to be cleaned or polished before each experiment. symbols are the same as previously defined . However , the toxic nature of mercury has restricted the Cathodic stripping voltammetry (CSV ) is the mirror broader use of this electrode for electroanalytical studies . image of ASV. CSV involves anodic deposition of the 5 Zeolite modified electrodes (ZMEs ) belong to a class of analyte , followed by stripping in the negative potential scan the so called “ chemically modified electrodes” (CMEs ) . as described by formula ( VI) . From an electrochemical perspective, zeolites offer a nano structured domain , where the physical structure and the A " - + Hg HgA + ne (VI ) : chemical nature of the zeolite affects electron transfer reac The resulting peak current provides the desired quantitative 10 tions and influences known chemical steps coupled with the information . CSV is used to measure a wide range of organic electron transfer at the electrode and solution interfaces . and inorganic compounds, capable of forming insoluble This results in the fabrication of electrodes with high sen salts with mercury . Examples are thiols or penicillin , as well sitivity , high selectivity , and a wide dynamic range . The as halide , cyanide, and sulfide ions. advent of zeolite modified electrodes ( ZMEs ) has over the Working electrodes are often employed in electroanalyti- 15 past 15 years attracted the attention of researchers in the field cal techniques. The working electrode (WE ) is a crucial of electrochemistry and other similar fields [ Walcarius , A., P. component of an electrochemical cell. This is because the Mariaulle , and L. Lamberts , Zeolite -modified solid carbon electron transfer of interest occurs at its surface . The selec paste electrodes. Journal of Solid State Electrochemistry , tion of the material for this electrode is therefore a critical 2003. 7 ( 10 ) : p . 671-677 . — incorporated herein by reference issue to the analysis . Several factors are considered when 20 in its entirety ]. In addition , the incorporation of zeolites into selecting the material for the working electrode . First , it carbon electrodes imparts a number of chemical , physical should possess favorable redox behavior with the analyte and structural features of high interest in the design and ( i.e. it should enable reproducible electron transfer without development of electroanalytical systems. These include electrode contamination ) . Second , the potential window shape, size and charge selectivities , physical and chemical over which the electrode works in a given electrolyte 25 stabilities , high ion exchange capacity as well as hydrophilic solution should be as wide as possible to allow for the character [Walcarius , A., Zeolite -modified electrodes in elec greatest degree of analyte characterization . Other factors troanalytical chemistry . Analytica Chimica Acta , 1999. 384 considered include the cost of the material , its ability to be ( 1 ) : p . 1-16 . — incorporated herein by reference in its turned into useful geometries , the ease of surface renewal entirety ). after analysis , and the material's toxicity [Imisides , M. D., 30 Zeolites are crystalline materials that afford molecular G. G. Wallace, and E. A. Wilke , Designing chemically sized frames and pores for excellent steric control of reac modified electrodes for electroanalysis . TrAC Trends in tion paths [Ojani , R., et al. , Electrochemical behavior of Analytical Chemistry , 1988. 7 (4 ) : p . 143-147 . — incorpo Ni( II ) incorporated in zeolite Y- modified carbon electrode : rated herein by reference in its entirety ] . The most com application for electrocatalytic oxidation of methanol in monly used working electrode materials are Pt, Au , C , and 35 alkaline solution . Journal of Solid State Electrochemistry , Hg. FIG . 7 presents examples of working electrodes 2011. 15 (9 ): p . 1935-1941. — incorporated herein by refer employed in electroanalytical chemistry . ence in its entirety ]. The major building units of zeolites are As a result of its inertness , platinum (Pt ) is one of the most [S10214 and [ A10 ]5- tetrahedral. These units can link in preferred electrodes in electroanalytical studies. However, several ways , resulting in arrays producing three -dimen the major drawback to the use of this electrode , aside from 40 sional anionic networks. The extra negative charge on its high cost is that the presence of small amounts of water [ A10 ]$ - tetrahedral is counter balanced by a cation , main or acid in the electrolyte leads to the reduction of hydrogen taining the overall neutrality of the zeolite . Zeolites have ion to form hydrogen gas at fairly modest negative poten been used for various industrial and catalytic purposes , the tials . This reduction interferes with any useful analytical most important of which is their use in fluid catalytic signal. Gold (Au ) electrodes have limited application in the 45 cracking (FCC ) which supplies about 45 % of the global positive potential range due to the ease of oxidation at their gasoline pool by the cracking of larger hydrocarbons into the surface. Hence , this electrode is not generally preferred in respective gasoline fractions [ Taarning , E., et al. , Zeolite electrochemical studies . Carbon ( C ) electrodes have advan catalyzed biomass conversion to fuels and chemicals . tages over platinum and gold electrodes because they enable Energy & Environmental Science , 2011. 4 ( 3 ) : p . 793-804 . scans to more negative potentials , and possess good anodic 50 incorporated herein by reference in its entirety ] . Today , over potential windows. The most prevalent form of carbon 200 zeolite and zeotype structures are recognized by the electrode is glassy carbon , which is relatively costly and International Zeolite Association ( IZA ), which includes difficult to machine . Carbon paste electrodes have also found MFI, BEA , MEL , MTW , MOR , FER , FAU , etc. [Pophale , usefulness in several applications. These electrodes are R., P. A. Cheeseman , and M.W. Deem , A database of new made from a paste of finely granulated carbon mixed with an 55 zeolite -like materials . Physical Chemistry Chemical Phys oil substrate (usually Nujol or paraffin ). The resulting paste ics, 2011. 13 ( 27 ) : p . 12407-12412 . — incorporated herein by is then packed into the cavity of an inert electrode body . reference in its entirety ]. These electrodes have the drawback of being susceptible to In the past, the composition of zeolites was limited to mechanical damage during use . Mercury (Hg ) is another aluminosilicate polymorphs. However , in recent years het classic type of electrode material. Due to its high hydrogen 60 eroatoms such as Ta , Ge, Fe, V , Sn , P , Ti , and B , among overvoltage , it can extend the cathodic potential window . In others are now incorporated into the zeolite structure along addition , mercury electrodes possess a highly reproducible , side silicon and aluminum [Moliner , M., C. Martinez , and A. renewable and smooth surface , which is very beneficial in Corma, Synthesis Strategies for Preparing Useful Small electrochemical analyses . Among the mercury electrodes , Pore Zeolites and Zeotypes for Gas Separations and Cataly the dropping mercury electrode (DME ) is the most com- 65 sis . Chemistry of Materials , 2014. 26 (1 ) : p . 246-258 . monly preferred . This is because in these electrodes drops of incorporated herein by reference in its entirety ] . This large mercury form and fall off continuously during a potential chemical utility has enable the control of the physicochemi US 10,495,601 B2 9 10 cal activities of zeolites ( such as acidity , redox properties, or 67-74 . each incorporated herein by reference in its hydrophobic - hydrophilic nature ), and as a result , there has entirety ] . By virtue of the small nature of the latter axis , been an increased number of applications of these materials molecules are unable to pass through and as such mordenite [Davis , M.E. and R. F. Lobo , Zeolite and molecular sieve synthesis . Chemistry ofMaterials , 1992.4 ( 4 ): p . 756-768.— 5 is generally regarded as a one- dimensional zeolite [Li , X., R. incorporated herein by reference in its entirety ]. More Prins, and J. A. van Bokhoven , Synthesis and characteriza recently , the introduction of additional rare earth (RE ) tion of mesoporous mordenite . Journal of Catalysis , 2009 . elements such as La and Ce into zeolite compositions with 262 ( 2 ) : p . 257-265 . — incorporated herein by reference in its the aim of improving the stability and enhancing the zeolite entirety ) . Due to its high thermal and acid stabilities , activity has been investigated [ Sousa - Aguiar, E. F., F. E. 10 mordenite has been used in several applications, such as in Trigueiro , and F. M.Z. Zotin , The role of rare earth elements the separation of gas or liquid mixtures and in catalysis such in zeolites and cracking catalysts . Catalysis Today, 2013 . as hydrocracking , hydro -isomerization , alkylation , reform 218-219 (0 ) : p . 115-122.— incorporated herein by reference ing , dewaxing and in the synthesis of dimethyl amines [Lu , in Severalits entiretyl authors have reported the improvement in the 15 B., et al. , Direct synthesis of high -silica mordenite using stability of zeolites after the addition of rare earth elements seed crystals . Microporous and Mesoporous Materials , such as La, Ce , Nd , Sm , and Pr. Such properties have been 2004. 76 ( 1-3 ) : p . 1-7 ; and Fernandes , L. D., et al ., Ethyl attributed to the formation of hydroxyl rare earth cation benzene hydroisomerization over bifunctional zeolite based species in zeolite channels [Bartlett , J. R., R. P. Cooney, and 20 catalysts : The influence of framework and extraframework R. A. Kydd, Hydrolysis of europium cations in zeolite X : A composition and zeolite structure. Journal of Catalysis , fourier transform infrared spectroscopic study . Journal of 1998. 177 ( 2 ) : p . 363-377.— each incorporated herein by Catalysis , 1988. 114 ( 1 ) : p . 53-57.— incorporated herein by reference in its entirety ] . Additionally , more recently , it has reference in its entirety ]. It was also found that the incor been considered for use in semiconductors, chemical sen poration of rare earth element ions into zeolite frameworks 25 sors, and nonlinear optical materials . FIG . 8 shows the tends to alter the Lewis acid sites in the framework , and this framework of mordenite zeolite [Baerlocher , C., L. B. in turn enhances the zeolite's catalytic activity [Pang , X., et McCusker, and D. H. Olson , MOR — Cmcm , in Atlas of al. , Effects of metal modifications of Y zeolites on sulfur Zeolite Framework Types (Sixth Edition ), C. Baerlocher and reduction performance in fluid catalytic cracking process . 30 L. B. M. H. Olson , Editors . 2007, Elsevier Science B. V.: Catalysis Today, 2007. 125 (3-4 ): p . 173-177. — incorporated Amsterdam . p . 218-219 . — incorporated herein by reference herein by reference in its entirety ) . Zeolites are also made in its entirety ) . catalytically more active and thermally more stable at their Several reports have been published on the role played by operating temperatures by incorporating rare earth element ions in them [Gu , J. , et al ., Hydrothermal incorporation of 35 metals in enhancing the electrocatalytic activity of zeolites Ce (La ) ions into the framework of ZSM - 5 by a multiple [Kaur , B., M. U. Anu Prathap , and R. Srivastava , Synthesis pH -adjusting co -hydrolysis . Journal of Porous Materials , of Transition -Metal Exchanged Nanocrystalline ZSM - 5 and 2013. 20 ( 1 ) : p . 7-13 . — incorporated herein by reference in Their Application in Electrochemical Oxidation of Glucose its entirety ]. The introduction of rare earth elements is used and Methanol. ChemPlus Chem , 2012. 77 (12 ) : p . 1119-1127 ; to adjust the amount and intensity of distribution of the acid 40 and Mojovi? , Z., et al. , Carbon monoxide electrooxidation sites in the zeolites . For example in FCC , catalysts are on Pt and PtRu modified zeolite X. Journal of Porous generally used at high temperatures and in hydrothermal Materials , 2012. 19 ( 5 ): p . 695-703; and Guzmán - Vargas, A., environments . These conditions usually induce a decline in et al. , Efficient electrocatalytic reduction of nitrite species on theleaching degree framework of crystallinity and consequent, deterioration collapse of thein thealuminum zeolite 45 zeolite modified electrode with Cu -ZSM -5 . Electrochimica structure , which result in the deactivation of the catalyst . The Acta , 2013. 108 ( 0 ): p . 583-590 ; and Raoof, J. B., et al. , introduction of rare earth element ions into the zeolite Synthesis of ZSM - 5 zeolite : Electrochemical behavior of framework was therefore reported to help stabilize the carbon paste electrode modified with Ni ( II ) -zeolite and its zeolite framework [ Zhan , W., et al. , Current status and 50 application for electrocatalytic oxidation of methanol. Inter perspectives of rare earth catalytic materials and catalysis . national Journal of Hydrogen Energy , 2011. 36 (20 ): p . Chinese Journal of Catalysis , 2014. 35 ( 8 ) : p . 1238-1250 . 13295-13300 ; and Li, Y.-J. and C.-Y. Liu , Silver- exchanged incorporated herein by reference in its entirety ) . zeolite Y -modified electrodes : size selectivity for anions. Mordernite is an industrially important member of the 55 Journal of Electroanalytical Chemistry , 2001. 517 (1-2 ) : p . zeolite family with the ideal composition of 117-120 ; and Cao , L., J. Jia , and Z. Wang , Sensitive deter Na Al Si40096.nH2O . Its framework is built on 5 -mem mination of Cd and Pb by differential pulse stripping vol bered rings arranged in columns parallel to the [ 001 ] axis . tammetry with in situ bismuth -modified zeolite doped carbon ÅHence ) tunnels, the frameworkparallel to includesthe c- axis elliptical and ( 2.6x5.7micropore Á) ( 6.7x7.0 tunnels 60 paste electrodes. Electrochimica Acta , 2008. 53 (5 ) : p. 2177 parallel to the b -axis [ Aly, H.M. , M.E. Moustafa , and E. A. 2182 , and Kaur, B. and R. Srivastava , Simultaneous elec Abdelrahman , Synthesis of mordenite zeolite in absence of trochemical determination of nanomolar concentrations of organic template . Advanced Powder Technology, 2012 . aminophenol isomers using nanocrystalline zirconosilicate 23 ( 6 ): p . 757-760 ; and Sano , T. , et al. , Synthesis of large 65 modified carbon paste electrode. Electrochimica Acta , 2014 . mordenite crystals in the presence of aliphatic alcohol. 141 ( 0 ): p . 61-71. each incorporated herein by reference in Microporous and Mesoporous Materials , 2001. 46 ( 1) : p . its entirety ) . Table 2 summarizes some of these studies. US 10,495,601 B2 11 12 TABLE 2 Summary of zeolite literature Metal Characterization Zeolite impregnated Technique Application Reference Zeolite Y Ni Cyclic voltammetry Electroanalytic Ojani, et al. oxidation of methanol in alkaline solution ZSM - 5 Cu , Ni, Co , Cyclic voltammetry Electrochemical Kaur, et al. Fe , and Mn oxidation of glucose and methanol Zeolite X Pt and Pt/ Ru Cyclic voltammetry Carbon monoxide Mojovic , et electrooxidation al. ZSM - 5 Cu Cyclic voltammetry Electrocatalytic Guzman reduction of nitrite Vargas, et al. species ZSM - 5 Ni Cyclic voltammetry Electrocatalytic Raoof, et al . oxidation of methanol Zeolite Y Ag Cyclic voltammetry Electroactiviry in Li, et al. aqueous solutions of different anions Synthetic Bi Differential pulse Determination of Cao , et al. zeolite square wave trace amounts of Cd voltammetry and Pb ZSM - 5 Zr Cyclic voltammetry Simultaneous Kaur, et al. electrochemical determination of nano -molar concentrations of aminophenol isomers

30 In one study , Li, et al. examined the electrochemical In another study, the analytical performance of a Bi performance of an Ag ion - incorporated zeolite Y -modified modified zeolite doped carbon paste electrode was investi electrode in aqueous solution containing different anions. It gated for trace analysis of Cd and Pb . Bi ion was incorpo was shown that the Ag ion -exchanged zeolite Y -modified rated into a commercial zeolite ( synthetic zeolite ) and this electrode has a high selectivity for Cl- and Br- anions. In 35 was used in the preparation of the modified electrode by other research , Kauer, et al. investigated the role played by mixing with graphite and silicone oil (binder ). The electro various transition metals in the electrocatalytic oxidation of chemical behavior of this electrode was studied by a strip glucose on a ZSM - 5 modified electrode. Metals studied ping technique in 0.10 M sodium acetate buffer solution ( pH included Cu , Ni, Co , Fe and Mn. It was found that a 4.5 ) before its application for the determination of Cd an Pb non - enzymatic electrochemical sensor based on a Ni2 + 40 levels . It was found that the in situ plated (zeolite / graphite exchanged nanocrystalline ZSM - 5 -modified electrode powder/ silicone, 10/190/80 w / w ) exhibited the most sensi exhibited the highest sensing ability towards oxidation tive response to Cd and Pb in 0.10 M acetate buffer , and the whereas the corresponding Cu2 + exchanged electrode exhib detection limits of 0.08 ugL - 1 and 0.10 ugl -- were obtained its the highest current sensitivity for glucose oxidation . It for Cd ( II ) and Pb ( II ) , respectively . The results obtained were was therefore concluded that the enhancement in the elec- 45 found to agree with those obtained by atomic absorption trocatalytic activities of nanocrystalline ZSM -5 modified spectroscopy (AAS ) . The role played by metals such as Zr, electrodes is due to the enhanced accessibility of glucose / Ti, and Al when incorporated into zeolite -modified elec methanol to M2 + active centers in the nanocrystalline trodes was also studied by Kaur, et al . using nano - ZSM - 5 ZSM - 5 owing to its large specific surface area and inter zeolite . The electrochemical behavior of this electrode stud crystalline mesopores. 50 ied by cyclic voltammetry revealed that a nano -Zr - ZSM - 5 / Guzman , V., et al. also studied the effect of Cu ( II ) ion carbon paste electrode exhibited excellent stability , high incorporation into ZSM - 5 modified electrode in the reduc sensitivity and selectivity . This electrode was applied in the tion of nitrite species. It was found that the Cu ( II ) ion determination of nanomolar concentrations of aminophenol incorporated modified electrode exhibits good electrocata isomers and the detection limits were found to be 26 nM , 30 lytic activity towards the reduction of nitrite species. It was 55 nM , and 30 nM for p - aminophenol, o - aminophenol, and also found that the activity increases as the Si/ Al ratio of the m - aminophenol, respectively . zeolite decreases. The influence of incorporating Ni( II ) ion In view of the forgoing , one object of the present disclo into the framework of zeolite Y for the electrocatalytic sure is to provide zeolite modified electrodes designed oxidation ofmethanol was also investigated by Ojani, et al . towards trace metal analysis , specifically rare earth metal It was found that the modified electrode prepared by both 60 impregnated zeolite modified carbon past electrodes (RE methods of cation exchange and open circuit accumulation ZMCPEs) such as lanthanum and cerium incorporated of Ni ion on the surface of the electrode displayed advan mordenite zeolite electrodes. This disclosure provides the tageous catalytic activity in alkaline solution . They also synthesis and characterization of these materials and elec studied the effect of the ratio of graphite to zeolite on trodes . An additional aspect of the present disclosure is electrocatalytic current and found that the ratio of 3 : 1 of 65 application of these electrodes in methods of electroanalyti graphite to zeolite was the determined ratio for advanta cal voltammetric detection and quantification ofheavy metal geous electrocatalytic activity . ions in aqueous solutions, such as the square wave anodic US 10,495,601 B2 13 14 stripping voltammetric determination of Cd ( II) and Pb ( II ) in In one embodiment, the rare earth metal is cerium and the aqueous samples. It is envisioned that these electrodes will heavy metal ion is Cd ( II ) , and the method has a Cd ( II ) display low detection limits , at or below the maximum detection limit in the range of 0.01-0.10 ug L- ?. contaminant level, with good reproducibility . Overall , the In one embodiment, the method has a reproducibility as electrodes of the present disclosure are envisaged to exhibit 5 measured by a relative standard deviation in the range of strong potential utility in the analysis of environmental 1-5 % . samples due to their inexpensiveness, ease of fabrication and The foregoing paragraphs have been provided by way of relative lack of toxicity compared to alternative electrodes, general introduction , and are not intended to limit the scope such as mercury based electrodes. of the following claims. The described embodiments , 10 together with further advantages , will be best understood by BRIEF SUMMARY OF THE INVENTION reference to the following detailed description taken in conjunction with the accompanying drawings . According to a first aspect , the present disclosure relates to an electrode comprising : i) graphite powder, ii) paraffin BRIEF DESCRIPTION OF THE DRAWINGS oil, and iii ) a zeolite impregnated with a rare earth metal . 15 In one embodiment, the zeolite is a mordenite zeolite A more complete appreciation of the disclosure and many which has a silica to alumina ratio in the range of 5 to 40 . of the attendant advantages thereof will be readily obtained In one embodiment, the rare earth metal is at least one as the same becomes better understood by reference to the selected from the group consisting of lanthanum and cerium . 20 following detailed description when considered in connec In one embodiment, the zeolite impregnated with the rare tion with the accompanying drawings , wherein : earth metal has a weight percentage of the rare earth metal FIG . 1 is an exemplary cyclic voltammetry (CV ) volta in the range of 1-15 % relative to the total weight of the mmogram of a single electron redox system . zeolite impregnated with the rare earth metal . FIG . 2 is an exemplary linear sweep voltammetry (LSV ) In one embodiment, the electrode has weight percentage 25 voltammogram of ferrocene . of the graphite powder in the range of 45-75 % relative to the FIG . 3 is an exemplary normal pulse voltammetry (NPV ) total weight of the electrode . signal. In one embodiment, the electrode has a weight percentage FIG . 4 is an exemplary differential pulse voltammetry of the zeolite impregnated with the rare earth metal in the (DPV ) signal . range of 1-30 % relative to the total weight of the electrode. 30 FIG . 5 is an exemplary square wave cycle waveform . In one embodiment, the electrode has a weight percentage FIG . 6 is exemplary square wave voltammograms for a of the paraffin oil in the range of 20-40 % relative to the total reversible electron transfer including forward current ( A ) , weight of the electrode . reverse current (B ), and net difference current (C ). In one embodiment, the electrode has a 10-40 % greater FIG . 7 is a depiction of exemplary working electrodes electroactive surface area relative to a substantially similar 35 including empty tip (A ), platinum (B ), gold (C ), silver (D ), electrode lacking the zeolite impregnated with the rare earth and glassy carbon (E ). metal . FIG . 8 is a depiction of the mordenite zeolite framework . According to a second aspect , the present disclosure FIG . 9 is a composite electrode used as working electrode relates to a method for detecting and quantifying a heavy comprising rare earth impregnated zeolite modified carbon metal ion in an aqueous solution comprising : i ) contacting 40 paste and copper wire as an electrical contact . the aqueous solution with the electrode in any of its embodi FIG . 10 is X -ray diffraction (XRD ) patterns of mordenite ments , ii ) generating a negative deposition potential at the zeolite synthesized at 180 ° C. for 48 h with different silica electrode to reduce the heavy metal ion and form a reduced to alumina ratios including 10 (a ), 15 (b ), 20 (c ), 25 (d ), and heavy metal that is deposited onto the electrode , iii ) scan 30 (e ). ning a potential range from the negative deposition potential 45 FIG . 11 is a scanning electron microscopy (SEM ) micro in the positive direction at the electrode to oxidize and strip graph of mordenite zeolite crystals with a silica to alumina the reduced heavy metal from the electrode, and iv ) mea ratio of 15 . suring the current during the scanning . FIG . 12 is a scanning electron microscopy (SEM ) micro In one embodiment, the heavy metal ion is at least one graph of mordenite zeolite crystals with a silica to alumina selected from the group consisting of Pb ( II ) and Cd ( II) . 50 ratio of 20 . In one embodiment, the scanning and the measuring are FIG . 13 is a scanning electron microscopy (SEM ) micro performed with square wave voltammetry . graph ofmordenite zeolite crystals with a silica to alumina In one embodiment, the negative deposition potential is in ratio of 25 . the range of -2.0 V to -0.2 V. FIG . 14 is a scanning electron microscopy (SEM ) micro In one embodiment, the scanning is performed at a scan 55 graph of mordenite zeolite crystals with a silica to alumina rate of 2-500 mV s - 1 . ratio of 30 . In one embodiment, the reduced heavy metal is deposited FIG . 15 is an energy dispersive X - ray (EDX ) spectrum of over a time period in the range of 10-250 seconds . a lanthanum impregnated mordenite zeolite (La -MOR -15 ). In one embodiment, the rare earth metal is lanthanum and FIG . 16 is 27Al magic angle spinning nuclear magnetic the heavy metal ion is Pb ( II ) , and the method has a Pb ( II ) 60 resonance (MAS NMR ) spectra of a mordenite zeolite detection limit in the range of 0.15-0.30 ug L - 1. (MOR -15 ) before rare earth metal impregnation ( a ) and after In one embodiment, the rare earth metal is lanthanum and lanthanum (La ) impregnation ( b ) . the heavy metal ion is Cd ( II ) , and the method has a Cd ( II ) FIG . 17 is cyclic voltammetry (CV ) voltammograms for detection limit in the range of 0.05-0.20 ug L - 1. a 10 mM K4Fe( CN ) , solution and 0.1 M KCl at a scan rate In one embodiment, the rare earth metal is cerium and the 65 of 100 mV s- 1 (pH = 7 ) at La -MOR -15 composites with the heavy metal ion is Pb ( II ), and the method has a Pb ( II ) graphite : zeolite :paraffin ratio of 70 : 0 : 30 ( A ) , 65 : 5 : 30 ( B ) , detection limit in the range of 0.02-0.15 ug L - 1. 60:10:30 ( C ) , and 50:20:30 ( E ) . US 10,495,601 B2 15 16 FIG . 18 is a plot of peak current for La -MOR - 15 com FIG . 31 illustrates SWASV voltammograms in 0.1 M posites versus La- MOR -15 content percentage for zeolite phosphate buffer (pH = 4 ) at a La- MOR - 15 composite B modified carbon paste electrodes . zeolite modified carbon paste electrode with the graphite : FIG . 19 illustrates the effect of scan rate ( 5-400 mV s- ) zeolite : paraffin ratio of 65: 5 : 30 at an accumulation potential on the peak current of a La -MOR - 15 composite B electrode 5 of -1.2 V, an accumulation time of 120 seconds, an ampli tude of 100 mV, a frequency of 40 Hz, and a potential step with the graphite :zeolite :paraffin ratio of 65: 5 : 30 in the of 5 mV over 5 consecutive runs . presence of 10 mM K4Fe (CN ) , solution and 0.1 M KC1 FIG . 32 is X - ray diffraction ( XRD ) patterns of the Na (pH = 7 ) . MOR ( a ) and H -MOR ( b ) mordenite zeolite crystal forms FIG . 20 is a plot of the peak current for the La -MOR - 15 10 with a silica to alumina ratio of 15 prior to and after ion composite B electrode with the graphite : zeolite :paraffin exchange . ratio of 65 : 5 :30 versus the square root of the scan rate . FIG . 33 is a scanning electron microscopy (SEM ) micro FIG . 21 illustrates the effect of scan rate (5-400 mV s -1 ) graph ofmordenite zeolite crystals with a silica to alumina on the peak current of a La- MOR - 15 composite A electrode ratio of 15 (MOR - 15 ) . with the graphite :zeolite :paraffin ratio of 70 :0 :30 in the 15 FIG . 34 is an energy dispersive X - ray (EDX ) spectrum of presence of 10 mM K4Fe (CN ) solution and 0.1 M KC1 mordenite zeolite with a silica to alumina ratio of 15 ( pH = 7 ) . (MOR - 15 ) . FIG . 22 is a plot of the peak current for the La -MOR - 15 FIG . 35 is X -ray diffraction (XRD ) patterns ofmordenite composite A electrode with the graphite : zeolite: paraffin ratio zeolite with a silica to alumina ratio of 15 ( H -MOR -15 ) of 70 : 0 :30 versus the square root of the scan rate . 20 before lanthanum impregnation (a ) and after lanthanum FIG . 23 illustrates the effect of varying accumulation impregnation with different loadings of lanthanum including potential (-1.4 V to -0.6 V ) on the square wave anodic 2 wt % La -MOR (b ), 5 wt % La- MOR (c ), and 10 wt % stripping voltammetry (SWASV ) voltammograms of 500 La- MOR (d ) . ppb Cd ( II ) in 0.1 M phosphate buffer ( pH = 4 ) at a La- MOR FIG . 36 is X - ray diffraction (XRD ) patterns ofmordenite 15 composite B zeolite modified carbon paste electrode with 25 zeolite with a silica to alumina ratio of 15 (H -MOR -15 ) the graphite :zeolite :paraffin ratio of 65 :5 :30 at an accumu before cerium impregnation (a ) and after cerium impregna lation time of 120 seconds, an amplitude of 0.2 V , a tion with different loadings of cerium including 2 wt % frequency of 40 Hz, and a potential step of 5 mV. Ce -MOR ( b ) , 5 wt % Ce -MOR ( C ) , and 10 wt % Ce- MOR FIG . 24 is a plot of the current for a La- MOR - 15 (d ) . composite B zeolite modified carbon paste electrode with 30 FIG . 37 is a scanning electron microscopy ( SEM ) micro the graphite :zeolite :paraffin ratio of65 : 5 :30 versus accumu graph ofmordenite zeolite crystals with a silica to alumina lation potential. ratio of 15 and impregnated with 2 wt % lanthanum ( 2 wt % FIG . 25 illustrates the effect of varying accumulation time La -MOR ). ( 20-200 seconds ) on the SWASV voltammograms of 500 FIG . 38 is a scanning electron microscopy (SEM ) micro ppb Cd ( II) in 0.1 M phosphate buffer (pH = 4 ) at a La -MOR- 35 graph of mordenite zeolite crystals with a silica to alumina 15 composite B zeolite modified carbon paste electrode with ratio of 15 and impregnated with 5 wt % lanthanum ( 5 wt % the graphite : zeolite :paraffin ratio of 65 : 5 : 30 at an accumu La - MOR ) . lation potential of -1.2 V , an amplitude of 0.2 V , a frequency FIG . 39 is a scanning electron microscopy (SEM ) micro of 40 Hz, and a potential step of 5 mV. graph ofmordenite zeolite crystals with a silica to alumina FIG . 26 is a plot of the current for a La -MOR - 15 40 ratio of 15 and impregnated with 10 wt % lanthanum ( 10 wt composite B zeolite modified carbon paste electrode with % La -MOR ). the graphite :zeolite :paraffin ratio of65 : 5 :30 versus accumu FIG . 40 is a scanning electron microscopy ( SEM ) micro lation time. graph ofmordenite zeolite crystals with a silica to alumina FIG . 27 illustrates the effect of varying Cd( II) concentra ratio of 15 and impregnated with 2 wt % cerium (2 wt % tion ( 50-500 ppb ) on the SWASV voltammograms in 0.1 M 45 Ce -MOR ) . phosphate buffer ( pH = 4 ) at a La -MOR - 15 composite B FIG . 41 is a scanning electron microscopy (SEM ) micro zeolite modified carbon paste electrode with the graphite : graph ofmordenite zeolite crystals with a silica to alumina zeolite :paraffin ratio of 65 : 5 : 30 at an accumulation potential ratio of 15 and impregnated with 5 wt % cerium ( 5 wt % of -1.2 V , an accumulation time of 120 seconds, an ampli Ce -MOR ) . tude of 100 mV, a frequency of 40 Hz , and a potential step 50 FIG . 42 is a scanning electron microscopy (SEM ) micro of 5 mV. graph ofmordenite zeolite crystals with a silica to alumina FIG . 28 illustrates the effect of varying Cd ( II ) concentra ratio of 15 and impregnated with 10 wt % cerium ( 10 wt % tion (5-50 ppb ) on the SWASV voltammograms in 0.1 M Ce -MOR ). phosphate buffer (pH = 4 ) at a La -MOR - 15 composite B FIG . 43 is 27Al magic angle spinning nuclear magnetic zeolite modified carbon paste electrode with the graphite : 55 resonance (MAS NMR ) spectra of a mordenite zeolite zeolite :paraffin ratio of 65 : 5 : 30 at an accumulation potential (MOR - 15) before rare earth metal impregnation ( a ) and after of -1.2 V , an accumulation time of 120 seconds, an ampli lanthanum (La ) or cerium (Ce ) impregnation including 2 wt tude of 100 mV, a frequency of 40 Hz, and a potential step % La/ Ce -MOR (b ), 5 wt % La /Ce - MOR ( c ), and 10 wt % of 5 mV. La/ Ce - MOR ( d ). FIG . 29 is a calibration plot for a La -MOR - 15 composite 60 FIG . 44 illustrates the effect of varying lanthanum loading B zeolite modified carbon paste electrode with the graphite : ( 0 wt % to 10 wt % ) on the square wave anodic stripping zeolite :paraffin ratio of 65 : 5 : 30 of Cd ( II) concentrations voltammetry (SWASV ) voltammograms of 500 ppb Pb ( II ) from 50-500 ppb . in 0.1 M phosphate buffer (pH = 4 ) at a La- MOR - 15 zeolite FIG . 30 is a calibration plot for a La -MOR -15 composite modified carbon paste electrode with the graphite :zeolite : B zeolite modified carbon paste electrode with the graphite : 65 paraffin ratio of 50:25:25 with lanthanum loadings of 2 wt % zeolite : paraffin ratio of 65 :5 :30 of Cd ( II) concentrations La ( a ) , 5 wt % La ( b ) and 10 wt % La (c ) or an unmodified from 5-50 ppb . mordenite zeolite carbon paste electrode of 0 wt % La ( d ) at US 10,495,601 B2 17 18 an accumulation potential of -1.2 V , an accumulation time metry ( SWASV ) voltammogramsof 500 ppb Pb ( II ) in 0.1 M of 120 seconds, a potential step of 5 mV, an amplitude of 50 phosphate buffer at pH = 4 ( a ), 0.1 M sulfate buffer at pH = 4 mV, and a frequency of 15 Hz . ( b ), and 0.1 M acetate buffer at pH = 4 at a 10 wt % FIG . 45 is a plot of the current for the La -MOR - 15 zeolite Ce- MOR - 15 zeolite modified carbon paste composite G modified carbon paste electrode with the graphite :zeolite : 5 electrode with the graphite :zeolite :paraffin ratio of 65 :5 : 30 paraffin ratio of 50:25:50 versus the weight percent of at an accumulation potential of -1.2 V , an accumulation time lanthanum (La ) loading , of 120 seconds, a potential step of 5 mV, an amplitude of 50 FIG . 46 illustrates the effect of varying cerium loading ( 0 mV, and a frequency of 15 Hz . wt % to 10 wt % ) on the square wave anodic stripping FIG . 55 is a graph of current for a 10 wt % Ce -MOR - 15 voltammetryin 0.1 M phosphate (SWASV buffer ) voltammograms (pH = 4 ) at a Ce of- MOR 500 -ppb 15 zeolitePb (II ) 10 zeolite modified carbon paste composite G electrode with modified carbon paste electrode with the graphite :zeolite : the graphite : zeolite :paraffin ratio of 65 :5 :30 in 0.1 M phos paraffin ratio of 50:25:25 with cerium loadings of 2 wt % Ce phate buffer (pH = 4 ) , 0.1 M sulfate buffer (pH = 4 ), and 0.1 M ( b ), 5 wt % Ce ( c ) and 10 wt % Ce ( d ) or an unmodified acetate buffer (pH = 4 ) . mordenite zeolite carbon paste electrode of 0 wt % Ce ( a ) at 15 FIG . 56 illustrates the effect of varying pH values ( 3 to 8 ) an accumulation potential of -1.2 V, an accumulation time on the square wave anodic stripping voltammetry (SWASV ) of 120 seconds, a potential step of 5 mV, an amplitude of 50 voltammograms of 500 ppb Pb ( II ) in 0.1 M phosphate buffer mV, and a frequency of 15 Hz. at a 2 wt % La -MOR - 15 zeolite modified carbon paste FIG . 47 is a plot of the current for the Ce -MOR - 15 zeolite composite B electrode with the graphite :zeolite :paraffin modified carbon paste electrode with the graphite: zeolite : 20 ratio of 65: 5: 30 at an accumulation potential of -1.2 V, an paraffin ratio of 50:25:50 versus the weight percent of accumulation time of 120 seconds, a potential step of 5 mV, cerium (Ce ) loading . an amplitude of 50 mV, and a frequency of 15 Hz. FIG . 48 illustrates the effect of varying electrode compo FIG . 57 is a plot of current for a 2 wt % La -MOR - 15 sition on the square wave anodic stripping voltammetry zeolite modified carbon paste composite B electrode with (SWASV ) voltammograms of 500 ppb Pb (II ) in 0.1 M 25 the graphite : zeolite : paraffin ratio of 65 : 5: 30 versus pH in 0.1 phosphate buffer (pH = 4 ) at a 2 wt % La -MOR - 15 zeolite M phosphate buffer supporting electrolyte . modified carbon paste electrode with the composite graphi FIG . 58 illustrates the effect of varying pH values ( 3 to 8 ) te : zeolite :paraffin ratio of 70 : 0 : 30 ( A ) ,65 : 5 : 30 ( B ) ,60:10:30 on the square wave anodic stripping voltammetry (SWASV ) ( C ) , 55:15:30 ( D ) and 50:20:30 ( E ) at an accumulation voltammograms of 500 ppb Pb ( II ) in 0.1 M phosphate buffer potential of -1.2 V , an accumulation time of 120 seconds, a 30 at a 10 wt % Ce- MOR - 15 zeolite modified carbon paste potential step of 5 mV, an amplitude of 50 mV, and a composite G electrode with the graphite :zeolite :paraffin frequency of 15 Hz. ratio of 65 :5 : 30 at an accumulation potential of -1.2 V , an FIG . 49 illustrates the effect of varying electrode compo accumulation time of 120 seconds, a potential step of 5 mV, sition on the square wave anodic stripping voltammetry an amplitude of 50 mV, and a frequency of 15 Hz. (SWASV ) voltammograms of 500 ppb Pb ( II ) in 0.1 M 35 FIG . 59 is a plot of current for a 10 wt % Ce -MOR - 15 phosphate buffer (pH = 4 ) at a 10 wt % Ce -MOR - 15 zeolite zeolite modified carbon paste composite G electrode with modified carbon paste electrode with the composite graphi the graphite :zeolite :paraffin ratio of65 : 5 :30 versus pH in 0.1 te : zeolite : paraffin ratio of 70 :0 : 30 ( F ) , 65 : 5 : 30 ( G ), 60:10:30 M phosphate buffer supporting electrolyte . ( H ) , 55:15:30 ( 1 ) and 50:20:30 ( J ) at an accumulation FIG . 60 is a plot of peak current versus amplitude and potential of -1.2 V , an accumulation time of 120 seconds , a 40 illustrates the effect of varying amplitude ( 0.05 V to 0.5 V ) potential step of 5 mV, an amplitude of 50 mV, and a of 500 ppb Pb ( II ) in 0.1 M phosphate buffer (pH = 4 ) at a 2 frequency of 15 Hz. wt % La -MOR - 15 zeolite modified carbon paste composite FIG . 50 is a graph of current for a 2 wt % La- MOR - 15 B electrode with the graphite zeolite : paraffin ratio of 65 : 5 : 30 zeolite modified carbon paste electrode with the composite at an accumulation potential of -1.2 V , an accumulation time graphite :zeolite :paraffin ratios of 70 :0 :30 ( A ), 65 :5 : 30 (B ), 45 of 120 seconds, a potential step of 5 mV, and a frequency of 60:10:30 ( C ) , 55:15:30 ( D ) and 50:20:30 ( E ) . 15 Hz. FIG . 51 is a graph of current for a 10 wt % Ce -MOR - 15 FIG . 61 is a plot of peak current versus amplitude and zeolite modified carbon paste electrode with the composite illustrates the effect of varying amplitude (0.05 V to 0.5 V ) graphite :zeolite :paraffin ratios of 70 :0 :30 (F ), 65 :5 :30 (G ), of 500 ppb Pb ( II ) in 0.1 M phosphate buffer (pH = 4 ) at a 10 60:10:30 ( H ) , 55:15:30 ( I ) and 50:20:30 ( J ) . 50 wt % Ce -MOR - 15 zeolite modified carbon paste composite FIG . 52 illustrates the effect of varying supporting elec G electrode with the graphite : zeolite : paraffin ratio of 65 : 5 : trolyte buffer on the square wave anodic stripping voltam 30 at an accumulation potential of -1.2 V , an accumulation metry (SWASV ) voltammograms of 500 ppb Pb ( II ) in 0.1 M time of 120 seconds, a potential step of 5 mV, and a phosphate buffer at pH = 4 ( a ), 0.1 M sulfate buffer at pH = 4 frequency of 15 Hz . ( b ) , and 0.1 M acetate buffer at pH = 4 at a 2 wt % La- MOR- 55 FIG . 62 is a plot of peak current versus frequency and 15 zeolite modified carbon paste composite B electrode with illustrates the effect of varying frequency (20 Hz to 200 Hz ) the graphite : zeolite :paraffin ratio of 65 : 5 : 30 at an accumu of 500 ppb Pb ( II ) in 0.1 M phosphate buffer (pH = 4 ) at a 2 lation potential of -1.2 V, an accumulation time of 120 wt % La- MOR - 15 zeolite modified carbon paste composite seconds, a potential step of 5 mV, an amplitude of 50 mV, B electrode with the graphite : zeolite : paraffin ratio of65 : 5 : 30 and a frequency of 15 Hz. 60 at an accumulation potential of -1.2 V , an accumulation time FIG . 53 is a graph of current for a 2 wt % La- MOR - 15 of 120 seconds, a potential step of 5 mV, and an amplitude zeolite modified carbon paste composite B electrode with of 300 mV. the graphite : zeolite :paraffin ratio of 65 :5 :30 in 0.1 M phos FIG . 63 is a plot of peak current versus frequency and phate buffer (pH = 4 ) , 0.1 M sulfate buffer (pH = 4 ), and 0.1 M illustrates the effect of varying frequency ( 20 Hz to 180 Hz) acetate buffer (pH = 4 ) . 65 of 500 ppb Pb ( II ) in 0.1 M phosphate buffer ( pH = 4 ) at a 10 FIG . 54 illustrates the effect of varying supporting elec wt % Ce -MOR - 15 zeolite modified carbon paste composite trolyte buffer on the square wave anodic stripping voltam G electrode with the graphite : zeolite : paraffin ratio of 65 : 5 : US 10,495,601 B2 19 20 30 at an accumulation potential of -1.2 V , an accumulation FIG . 73 is a calibration plot for a 2 wt % La -MOR - 15 time of 120 seconds, a potential step of 5 mV, and an zeolite modified carbon paste composite B electrode with amplitude of 300 mV. the graphite : zeolite :paraffin ratio of 65 : 5 : 30 of Pb ( II) con FIG . 64 is a plot of peak current versus deposition centrations from 5-50 ppb . potential (accumulation potential) and illustrates the effect 5 FIG . 74 illustrates the effect of varying Pb ( II ) concentra of varying deposition potential (-1.6 V to -0.4 V ) of 500 tion (50-500 ppb ) on the square wave anodic stripping ppb Pb ( II ) in 0.1 M phosphate buffer (pH = 4 ) at a 2 wt % voltammetry (SWASV ) voltammograms in 0.1 M phosphate La- MOR - 15 zeolite modified carbon paste composite B buffer (pH = 4 ) at a 10 wt % Ce -MOR - 15 zeolite modified electrode with the graphite :zeolite :paraffin ratio of 65: 5 :30 carbon paste composite G electrode with the graphite : at an accumulation time of 120 seconds, a potential step of 10 zeoliteseconds :paraffin , a deposition ratio ofpotential 65: 5 : 30 ofat -1.2 a deposition V , a potential time ofstep 120 of 5 mV, an amplitude of 100 mV, and a frequency of 60 Hz. 5 mV, an amplitude of 200 mV, and a frequency of 40 Hz. FIG . 65 is a plot of peak current versus deposition FIG . 75 is a calibration plot for a 10 wt % Ce -MOR - 15 potential (accumulation potential ) and illustrates the effect zeolite modified carbon paste composite G electrode with of varying deposition potential (-1.4 V to -0.4 V ) of 500 15 the graphite : zeolite :paraffin ratio of 65 : 5 : 30 of Pb ( II ) con ppb Pb ( II ) in 0.1 M phosphate buffer (pH = 4 ) at a 10 wt % centrations from 50-500 ppb . Ce -MOR - 15 zeolite modified carbon paste composite G FIG . 76 illustrates the effect of varying Pb ( II ) concentra electrode with the graphite : zeolite :paraffin ratio of 65 : 5 : 30 tion ( 5-50 ppb ) on the square wave anodic stripping volta at an accumulation time of 120 seconds, a potential step of mmetry (SWASV ) voltammograms in 0.1 M phosphate 5 mV, an amplitude of 200 mV, and a frequency of 40 Hz. 20 buffer (pH = 4 ) at a 10 wt % Ce -MOR - 15 zeolite modified FIG . 66 illustrates the effect of varying deposition (accu carbon paste composite G electrode with the graphite : mulation ) time (20-180 seconds) on the SWASV voltam zeolite : paraffin ratio of 65 : 5 :30 at a deposition time of 120 mograms of 500 ppb Pb (II ) in 0.1 M phosphate buffer seconds, a deposition potential of -1.2 V , a potential step of (pH = 4 ) at a 2 wt % La -MOR -15 zeolite modified carbon 5 mV, an amplitude of 200 mV, and a frequency of 40 Hz. paste composite B electrode with the graphite: zeolite : paraf- 25 FIG . 77 is a calibration plot for a 10 wt % Ce -MOR - 15 fin ratio of 65 : 5 :30 at a deposition potential of -1.2 V , a zeolite modified carbon paste composite G electrode with potential step of 5 mV, an amplitude of 100 mV, and a the graphite :zeolite :paraffin ratio of 65 :5 : 30 of Pb ( II ) con frequency of 60 Hz. centrations from 5-50 ppb . FIG . 67 is a plot of the current for a 2 wt % La -MOR - 15 FIG . 78 illustrates the effect of varying Cd ( II ) concentra zeolite modified carbon paste composite B electrode with 30 tion (50-500 ppb ) and Pb ( H ) concentration (50-500 ppb ) on the graphite : zeolite :paraffin ratio of 65: 5 : 30 versus deposi the square wave anodic stripping voltammetry (SWASV ) tion time (accumulation time) . voltammograms in 0.1 M phosphate buffer (pH = 4 ) at a 2 wt FIG . 68 illustrates the effect of varying deposition (accu % La -MOR - 15 zeolite modified carbon paste composite B mulation ) time (20-180 seconds) on the SWASV voltam electrode with the graphite : zeolite :paraffin ratio of 65 : 5 : 30 mograms of 500 ppb Pb ( II ) in 0.1 M phosphate buffer 35 at a deposition time of 120 seconds, a deposition potential of (pH = 4 ) at a 10 wt % Ce -MOR - 15 zeolite modified carbon -1.2 V , a potential step of 5 mV, an amplitude of 100 mV, paste composite G electrode with the graphite : zeolite :par and a frequency of 60 Hz. affin ratio of 65 : 5 : 30 at a deposition potential of -1.0 V , a FIG . 79 is a calibration plot for a 2 wt % La -MOR - 15 potential step of 5 mV, an amplitude of 200 mV, and a 40 zeolitethe graphite modified zeolite carbon : paraffin paste ratio composite of 65 : 5 : 30B electrodeof Cd (II )with and frequency of 40 Hz. Pb ( II ) concentrations from 50-500 ppb . FIG . 69 is a plot of the current for a 10 wt % Ce- MOR - 15 FIG . 80 illustrates the effect of varying Cd ( II ) concentra zeolite modified carbon paste composite G electrode with tion ( 50-500 ppb ) and Pb ( II ) concentration ( 50-500 ppb ) on the graphite : zeolite: paraffin ratio of 65 :5 : 30 versus deposi the square wave anodic stripping voltammetry (SWASV ) tion time (accumulation time) . 45 voltammograms in 0.1 M phosphate buffer (pH = 4 ) at a 10 wt FIG . 70 illustrates the effect of varying Pb ( II ) concentra % Ce -MOR -15 zeolite modified carbon paste composite G tion (50-500 ppb ) on the square wave anodic stripping electrode with the graphite: zeolite :paraffin ratio of 65: 5 :30 voltammetry (SWASV ) voltammograms in 0.1 M phosphate at a deposition time of 120 seconds, a deposition potential of buffer (pH = 4 ) at a 2 wt % La -MOR - 15 zeolite modified -1.2 V , a potential step of 5 mV, an amplitude of 200 mV, carbon paste composite B electrode with the graphite : zeo- 50 and a frequency of 40 Hz . lite :paraffin ratio of 65 : 5 : 30 at an accumulation potential of FIG . 81 is a calibration plot for a 10 wt % Ce -MOR - 15 -1.2 V , an accumulation time of 120 seconds , a potential zeolite modified carbon paste composite G electrode with step of 5 mV, an amplitude of 100 mV, and a frequency of the graphite : zeolite: paraffin ratio of 65: 5 :30 of Cd ( II) and 60 Hz . Pb ( II ) concentrations from 50-500 ppb . FIG . 71 is a calibration plot for a 2 wt % La- MOR - 15 55 zeolite modified carbon paste composite B electrode with DETAILED DESCRIPTION OF THE the graphite : zeolite :paraffin ratio of 65 : 5 : 30 of Pb ( II ) con EMBODIMENTS centrations from 50-500 ppb . FIG . 72 illustrates the effect of varying Pb ( II ) concentra Referring now to the drawings, wherein , like reference tion (5-50 ppb ) on the square wave anodic stripping volta- 60 numerals designate identical or corresponding parts mmetry (SWASV ) voltammograms in 0.1 M phosphate throughout the several views . Embodiments of the present buffer (pH = 4 ) at a 2 wt % La- MOR -15 zeolite modified disclosure will now be described more fully hereinafter with carbon paste composite B electrode with the graphite :zeo reference to the accompanying drawings , in which some, but lite :paraffin ratio of 65 : 5 :30 at an accumulation potential of not all of the embodiments of the disclosure are shown . -1.2 V , an accumulation time of 120 seconds, a potential 65 Within the description of this disclosure , where a numeri step of 5 mV, an amplitude of 100 mV, and a frequency of cal limit or range is stated , the endpoints are included unless 60 Hz . stated otherwise . Also , all values and subranges within a US 10,495,601 B2 21 22 numerical limit or range are specifically included as if paste electrodes belong to a special group of heterogeneous explicitly written out. As used herein , the words “ a ” and carbon electrodes. These electrodes are widely used mainly " an ” and the like carry the meaning of “ one or more ” . The for voltammetric measurements ; however, carbon paste phrases " selected from the group consisting of ” , “ chosen based sensors are also applicable in coulometry (both from " , and the like include mixtures of the specified mate 5 amperometry and potentiometry ) . In general, carbon paste rials . Terms such as “ contain ( s )” and the like are open terms electrodes are advantageous because carbon pastes are easily meaning " including at least " unless otherwise specifically obtainable at minimal costs and are especially suitable for noted . preparing an electrode material modified with admixtures According to a first aspect, the present disclosure relates ( i.e. zeolites ) of other compounds thus giving the electrode to an electrode comprising : i ) graphite powder , ii ) paraffin 10 certain predetermined properties . Electrodes prepared in this oil , and iii ) a zeolite impregnated with a rare earth metal . way can serve as highly selective sensors for both inorganic As used herein , an electrode refers to an electrical con and organic electrochemistry. Carbon paste electrodes , ductor used to make contact with a nonmetallic part of a glassy carbon paste electrodes , glassy carbon electrodes circuit ( i.e. a semiconductor , an electrolyte , a vacuum or air ) , (GCE ) , pyrolytic graphite electrodes (PyGE ) , etc. when preferably an electrolyte . In certain embodiments , the term 15 modified are termed as chemically modified electrodes . electrode may include the electroactive material of the Chemically modified electrodes have been employed for the electrode. In certain embodiments , the electrode of the analysis of inorganic and organic species . In a preferred present disclosure may be present in a holder or an electro embodiment the electrode is a rare earth metal impregnated chemical cell and the term electrode may refer to the full the zeolite modified carbon paste electrode representing a electrode in the holder and/ or the electrochemical cell. As 20 homogeneous mixture of the graphite powder, the paraffin used herein , an electrochemical cell refers to a device oil , and the zeolite impregnated with a rare earth metal . capable of either generating electrical energy from chemical In a preferred embodiment, the electrode of the present reactions or facilitating chemical reactions through the intro disclosure comprises graphite powder as a conductive car duction of electrical energy. The electrode in an electro bon . Graphite is essentially made up ofhundreds , preferably chemical cell may be referred to as either an anode or a 25 thousands or tens to hundreds of thousands of layers of cathode. As used herein , an anode refers to the electrode at graphene . As used herein , graphite ( or plumbago ) refers to which electrons leave the cell and oxidation occurs , and a a crystalline form of carbon , a semimetal , a native element cathode refers to the electrode at which electrons enter the mineral, and one of the allotropes of carbon . Graphite is the cell and reduction occurs. Each electrodemay become either most stable form of carbon under standard conditions . the anode or the cathode depending on the direction of 30 Graphite may be considered the highest grade of coal, just current through the cell. In addition a bipolar electrode above anthracite and alternatively called meta -anthracite . describes an electrode that functions as the anode of one cell Graphite has a layered , planar structure . In each layer the and the cathode of another cell . Chemically modified elec carbon atoms arranged in a honeycomb lattice with separa trodes are electrodes that have their surface chemically tion of 0.14-0.15 nm , preferably 0.14-0.145 nm or about modified to change the electrode's physical, chemical, elec- 35 0.142 nm and a distance between planes of 0.3-0.35 nm , trochemical , optical , electrical, and / or transport properties . preferably 0.32-0.345 nm , preferably 0.33-0.34 nm , or about These electrodes are used for advanced purposes in research 0.335 nm . Atoms in the plane are bonded covalently , with and investigation . only three of the four potential bonding sites satisfied . The As used herein , a chemically modified electrode (CME ) is fourth electron is free to migrate in the plane, making an electrical conductor (material that has the ability to 40 graphite electrically conductive; however , it does not con transfer electricity ) that has its surface or material modified duct in a direction at right angles to the plane. Bonding for different electrochemical functions. At a modified elec between the layers is via weak van der Waals bonds, which trode , an oxidation - reduction substance accomplishes elec allows layers of graphite to be easily separated , or to slide trocatalysis by transferring electrons from the electrode to a past each other . In one embodiment, the graphite material of reactant, or a reaction substrate . Electrodes can be modified 45 the electrode described herein comprises 10-500000 layers in a variety of ways including , but not limited to , adsorption of graphene , preferably 100-400000 layers of graphene , (chemisorption ) , covalent bonding , polymer film coating, preferably 500-300000 layers of graphene , preferably 1000 and composite formation . Composite formation refers to a 250000 layers of graphene, preferably 5000-200000 layers method that has the chemical modifier mixed with an of graphene , preferably 10000-150000 layers of graphene , electrode matrix material ( i.e. having a zeolite , the chemical 50 preferably 25000-125000 layers of graphene , preferably modifier , mixed with carbon particles in a carbon paste 50000-100000 layers of graphene. electrode, the electrode matrix ). Exemplary electrodes that The two known forms of graphite are alpha (a , hexagonal) can be chemically modified include, but are not limited to , and beta (ß , rhombohedral) . The two forms have very carbon paste electrodes , glassy carbon paste electrodes, similar physical properties, except the graphene layers stack glassy carbon electrodes , pyrolytic carbon electrodes , and 55 slightly differently . The hexagonal graphite may be either the like . Chemically modified electrodes have been flat or buckled . The alpha form can be converted to the beta employed for the analysis of a variety of organic and form through mechanical treatment and the beta form reverts inorganic species . to the alpha form when heated to sufficiently high tempera In a preferred embodiment, the electrode of the present tures ( ~ 1300 ° C.) . In terms of the present disclosure , the disclosure may be considered as a chemically modified 60 graphite material of the electrode described herein may be electrode (CME ), preferably a modified carbon paste elec alpha , beta , or mixtures thereof . trode (CPE orMCPE ) , specifically a zeolite modified carbon There are three principal types of natural graphite , each paste electrode ( ZMCPE ). As used herein , a carbon paste occurring in different types of ore deposit. Crystalline flake electrode refers an electrode made from a mixture of con graphite (or flake graphite ) occurs as isolated , flat , plate - like ducting graphite powder and a pasting liquid (i.e. paraffin 65 particles with hexagonal edges if unbroken and when broken oil) . These electrodes are simple to construct and offer an the edges can be irregular or angular. Amorphous graphite easily renewable surface for electron exchange . Carbon refers to very fine flake graphite . Lump graphite (or vein US 10,495,601 B2 23 24 graphite ) occurs in fissure veins or fractures and appears as codetermines principal physicochemical and electrochemi massive platy intergrowths of fibrous or acicular crystalline cal properties of the electrode . Typical parameters of a aggregates. Highly ordered or oriented pyrolytic graphite suitable pasting liquid or binder include, but are not limited (HOPG ) refers to graphite with an angular spread between to , chemical inertness and electroinactivity, low volatility , the graphite sheets of less than 1 ° . Graphite fiber is also 5 minimal solubility in water , and controlled miscibility with sometimes used to refer to carbon / fiber and /or carbon fiber organic solvents . reinforced polymer. In terms of the present disclosure , the In a preferred embodiment, the electrode of the present graphite material employed may be natural graphite , syn disclosure comprises paraffin (mineral ) oils as a pasting thetic graphite , crystalline flake graphite , amorphous graph liquid or binder . As used herein , mineral oil or paraffin oil ite , highly oriented pyrolytic graphite , lump graphite , graph- 10 refers to any of various colorless , odorless light mixtures of ite fiber , graphite nanofiber, chemically modified graphite , higher alkanes from a mineral source, particularly a distillate expanded graphite , intercalated graphite , and mixtures of petroleum . Most often , mineral oil is a liquid by -product thereof, preferably graphite in the form of flakes , rods, or of refining crude oil to make gasoline and other petroleum powder , most preferably commercially available graphite products . This type ofmineral oil is a transparent, colorless powder. 15 oil composed mainly of alkanes and cycloalkanes related to Exemplary commercially available graphite powders petroleum jelly . The mineral oil or paraffin oil of the present include, but are not limited to CR (Czech Republic ), RW disclosure may be light ,medium or heavy grade in terms of (Germany , Austria ) , BDH (Scandinavia and United King density and viscosity . The mineral oil or paraffin oil prefer dom ) , SMMC (China ), Acheson , UCP, GP , and SP (United ably has a density of 0.75-0.92 g /mL , preferably 0.80-0.90 States) . In a preferred embodiment, the graphite powder has 20 g/ mL , preferably 0.81-0.89 g/ mL , preferably 0.83-0.86 an average particle ( grain ) size in the ranges of micrometers g /mL and a viscosity of 5-15 mm-/ s , preferably 7-13 mm / s , or tens of micrometers , preferably 10-90 um , preferably preferably 8.5-11 mm²/ s . Three basic classes of mineral oils 10-50 um , preferably 15-40 um , preferably 20-30 um and a exist : i ) alkanes and alkane oils based on light n - alkanes , ii) relatively uniform particle size distribution ( i.e. 5-20 um ). In naphthenic oils , based on cycloalkanes, and iii ) aromatic some embodiments the graphite powder has an average 25 oils , based on aromatic hydrocarbons (distinct from essential particle ( grain ) size in the range of 20-100 nm , preferably oils ) . In terms of the present disclosure, the mineral oil or 30-80 nm . In certain embodiments , the graphite powder is paraffin oil may be an alkane oil , a naphthenic oil, an substantially free of impurities, such as oxygen , and pos aromatic oil, and mixtures thereof. Typical paraffin oil is sesses low adsorption capabilities, meaning the graphite formed by a mixture of liquid aliphatic hydrocarbons and is powder pure graphite content is greater than 80 % by weight 30 often marketed under a tradename. Exemplary suitable prod graphite relative to the total weight of the graphite powder , ucts of this kind include, but are not limited to Nujol and preferably greater than 85 % by weight , preferably greater Uvasol. than 90 % by weight, preferably greater than 95 % by weight, In a preferred embodiment, the electrode of the present preferably greater than 96 % by weight, preferably greater disclosure has a weight percentage of the paraffin oil in the than 97 % by weight, preferably greater than 98 % by weight, 35 range of 20-40 % relative to the total weight of the electrode, preferably greater than 99 % by weight, preferably greater preferably 22-38 % by weight, preferably 24-36 % by weight, than 99.5 % by weight, preferably greater than 99.9 % by preferably 26-34 % by weight , preferably 28-32 % by weight , weight, preferably greater than 99.99 % by weight, prefer or about 30 % by weight relative to the total weight of the ably greater than 99.995 % by weight pure graphite content electrode. In a preferred embodiment, the ratio of graphite to relative to the total weight of the graphite powder . 40 paraffin oil is in the range of 1.0 g graphite to 0.1-5.0 mL In a preferred embodiment, the electrode of the present paraffin oil , preferably 1.0 g graphite to 0.2-2.0 mL paraffin disclosure has a weight percentage of the graphite powder in oil, preferably 1.0 g graphite to 0.4-1.0 mL paraffin oil . the range of 45-75 % relative to the total weight of the It is equally envisaged that the electrode of the present electrode , preferably 50-70 % by weight, preferably 55-69 % disclosure may further comprise or may be adapted to by weight, preferably 60-68 % by weight, preferably 62-66 % 45 comprise additional pasting liquids or binders . Exemplary by weight, or about 65 % by weight relative to the total suitable pasting liquids or binders include , but are not weight of the electrode . limited to , aliphatic and aromatic hydrocarbons (Co -C20 It is equally envisaged that the electrode of the present C10 -C14 such as for example benzene , naphthalene , phenan disclosure may further comprise or may be adapted to threne , and hexadecane ), silicone oils and greases (polym comprise additional carbonaceous materials as conductive 50 erized siloxanes optionally with organic side chains, halo carbon . Exemplary suitable carbonaceousmaterials include, genated hydrocarbons and similar derivatives ( bromoform , but are not limited to , acetylene black (AB ), obtained by carbon tetrachloride, a -bromonaphthalene , p -dichloroben controlled combustion of acetylene in inert atmosphere or zene , and trans - 1,2 - dibromocyclohexane ), 1,2,3 - trichloro chemical decomposition , carbon black , an amorphous mate propane ( TCP ) , dioctyl phthalate (DOP ), di- iso -nonyl phtha rial obtainable by the incomplete combustion of heavy 55 late (DINP ) , 1-( 2 - nitrophenoxy ) octane (NPOE ), diphenyl petroleum fractions, colloidal graphite , hexagonal carbon ether , glycerol, castor oil, vaseline oil, polycationic electro with extremely fine flakes and enhanced conductivity , both lytes, room temperature ionic liquids (RTILs ) and the like . natural and synthetic forms of diamond applied as fine In a preferred embodiment, the electrode of the present powders , soot, activated charcoal, coal (“ black coal” ) , lig disclosure is a chemically modified carbon paste electrode , nite (“ brown coal ” ) , glassy carbon (GC ), fullerene ( C -60 ) , 60 preferably a zeolite modified carbon paste electrode, com carbon nanomaterials (carbon nanotubes, CNTs, carbon prising a zeolite as an electroactive material, preferably a nanohorns, carbon nanoparticles , carbon nanofibers ) , porous zeolite impregnated with a rare earth metal. As used herein , carbon foam , porous carbon microspheres , template carbon , a zeolite refers to a microporous aluminosilicate mineral. ordered mesoporous carbon (OMC ) and the like . Many zeolites occur naturally but are also produced indus Mechanical connection of the individual carbon particles 65 trially on a large scale . Zeolites are crystalline solid struc into a uniform mass is not the only role of binders . Each tures made of silicon , aluminum and oxygen that form a pasting liquid , including highly chemically inert substances , framework with cavities and channels inside where cations, US 10,495,601 B2 25 26 water , and / or small molecules may reside. Zeolites have a series ) , the stilbite framework (STI ; barrerite , stellerite , porous structure that can accommodate a wide variety of stilbite series ) ; brewsterite framework ( BRE ; brewsterite cations, such as Na + , K + , Ca2+ , Mg2 + and others . These series ), and mixtures thereof. Other acceptable structural positive ions are rather loosely held and can readily be group frameworks may include, but are not limited to , exchanged for others in a contact solution . Alternatively , 5 cowlesite , pentasil ( also known as ZSM - 5 , framework type zeolites are the aluminosilicate members of the family of MFI) , tschernichite (beta polymorph A , disordered frame microporous solids known as “molecular sieves ” . Several work , BEA ), Linde type A framework (zeolite A , LTA ), and varied unique zeolite frameworks have been discovered , at the like. In termsof the present disclosure , the zeolite and /or present there are nearly 200 unique zeolite frameworks the zeolite impregnated with a rare earth metal may have a identified and over 40 naturally occurring zeolite frame- 10 09.GA , 09.Gb, 09.GC , 09.GD , or 09.GE structural group works are known . Zeolites are crystalline materials that framework , preferably a 09.GD structural group framework . afford molecular sized frames and pores, the major building Often zeolites may be classified into groups according to units of zeolites are [Si04 ]4 and [A104 ] $ - tetrahedra . the Si/ Al ratio in their frameworks: i) “ low silica " or Zeolites are crystalline aluminosilicates with open 3D aluminum rich zeolites A and X ( silica to alumina molar framework structures built of SiO4 and A104 tetrahedra 15 ratio Si/ Al ~ 1 ) , ii ) “ intermediate silica ” zeolites such as for linked to each other by sharing all the oxygen atoms to form example zeolite Y , mordenite , zeolite L , and natural zeolites regular intra -crystalline cavities and channels of molecular ( silica to alumina molar ratio Si/ Al 2 to 5 ), and iii ) “ high dimensions . In a defining feature zeolite frameworks are silica ” zeolites such as zeolite beta and ZSM - 5 ( silica to made up of 4 - coordinated atoms forming tetrahedra . These alumina molar ratio Si/ Al210 ) . tetrahedra are linked together by their corners leading to a 20 The “ low silica ” zeolites represent a fortunate balance of wide variety of structures . These units can link in several composition , pore volume, and channel structure . These ways, resulting in arrays producing three - dimensional zeolites are nearly “ saturated ” in aluminum in the frame anionic networks . The extra negative charge on [ A104] 5 work composition with a molar ratio of Si/ Al ~ 1 , which is tetrahedra is counter balanced by a cation ,maintaining the considered the highest aluminum content possible in tetra overall neutrality of the zeolite . The framework structure 25 hedral aluminosilicate frameworks . Consequently , they con may contain linked cages, cavities, and /or channels which tain the maximum number of cation exchange sites balanc are big enough for small molecules to enter and/ or occupy. ing the framework aluminum , and thus the highest cation The system of large voids explains the low specific density contents and exchange capacities. These compositional of these compounds. characteristics provide the most highly heterogeneous sur In terms of the present disclosure a variety of zeolite 30 face known among porous materials , due to exposed cat mineral species may be suitable . The zeolite structural group ionic charges nested in an aluminosilicate framework which (Nickel - Strunz classification ) includes , but is not limited to , results in high field gradients . Their surfaces are highly 09.GA zeolites , 09.GB zeolites, 09.GC zeolites, 09.GD selective for water , polar, and polarizable molecules. The zeolites , 09.GE zeolites and mixtures thereof. The 09.GA “ intermediate silica ” zeolites represent superior stability zeolites with T3010 units ( T = combined Si and Al) are known 35 characteristics reflecting higher Si/ Al molar ratios ( 1.5-5 , as the fibrous zeolites and include , but are not limited to , the preferably 2.5-4 , preferably 3-3.5 ) that improve both ther natrolite framework (NAT ; gonnardite , natrolite , mesolite , mal and acid stability as aluminum positions in the zeolite paranatrolite , scolecite , tetranatrolite ) , the edingtonite frameworks pose a site of instability to attack by acid and framework (EDI ; edingtonite , kalborsite ), the thomsonite water vapor . In addition to improvement in stability the framework ( THO ; thomsonite series ) , and mixtures thereof. 40 difference in composition and structures provided additional The 09.GB zeolites with chains of single connected 4 -mem catalysis benefits . The “ high silica ” zeolites are zeolites with bered rings include, but are not limited to , the analcime molar Si/ Al ratios from 10 to 100 or higher , with distinct framework ( ANA ; analcime, leucite , pollucite , wairakite ) , surface characteristics . In contrast to the " low ” and “ inter laumontite (LAU ) , yugawaralite ( YUG ), goosecreekite mediate ” silica zeolites, representing heterogeneous hydro (GOO ), montesommaite (MON ), and mixtures thereof. The 45 philic surfaces within a porous crystal, the surface of the 09.GC zeolites with chains of doubly connected 4 -mem high silica zeolites is more homogeneous with an organo bered rings include, but are not limited to , the phillipsite philic - hydrophobic selectivity . They generally adsorb stron framework (PHI ; harmotome , phillipsite series ) , the gismon ger the less polar organic molecules and only weakly interact dine framework (GIS ; amicite gismondine, garronite , gob with water and other polar molecules. In terms of the present binsite ), boggsite (BOG ), merlinoite (MER ), the mazzite 50 disclosure , the zeolite and /or zeolite impregnated with a rare series (MAZ ), the paulingite series (PAU ) , perlialite (Linde earth metal may be a low silica zeolite , an intermediate silica type L framework , zeolite L , LTL ) , and mixtures thereof. zeolite , or high silica zeolite , preferably a high silica zeolite . The 09.GD zeolites with chains of 6 -membered rings are In a preferred embodiment, the zeolite of the electrode of the known as tabular zeolites and include, but are not limited to , present disclosure has a silica to alumina ratio in the range the chabazite framework (CHA ; chabazite series, hersche- 55 of 5 to 40, preferably 6 to 35 , preferably 7 to 30 , preferably lite , willhendersonite , SSZ - 13) , the faujasite framework 8 to 25 , preferably 9 to 22 , more preferably 10 to 20 , more (FAU ; faujasite series , Linde type X , zeolite X , X zeolites, preferably 12 to 18 , more preferably 14 to 16 , or about 15 . Linde type Y , zeolite Y , Y zeolites ), the mordenite frame In a preferred embodiment, the zeolite of the zeolite work (MOR ; maricopaite , mordenite ), the offretite -wenkite impregnated with a rare earth metal is a mordenite zeolite . subgroup 09.3D.25 such as offretite (OFF ) and wenkite 60 As used herein ,mordenite refers to a zeolite mineral with the (WEN ) , belilbergite ( TMA - E , Aiello and Barrer , framework general chemical formula (Ca , Na , K Al Si ,.024.7H2O , type EAB ) , bikitaite (BIK ) , the erionite series (ERI ) , ferri preferably Na Al Si40096.n -H2O , preferably having the erite ( FER ), gmelinite (GME ), the levyne series (LEV ) , the molar composition Na 0 :A1,0,30SiO2 : 780H , O . Morden dachiardite series (DAC ) , epistilbite (EPI ) , and mixtures ite is one of the six most abundant zeolites and is used thereof. The 09.GE zeolites with chains of T10020 tetrahedra 65 commercially . Mordenite is orthorhombic ( a ,b , c are all ( T = combined Si and Al) include , but are not limited to , the unequal and all angles are 90 degrees) . It often crystallizes heulandite framework (HEU ; clinoptilolite , heulandite in the form of fibrous aggregates , masses and vertically US 10,495,601 B2 27 28 striated prismatic crystals . It may be colorless , white , or zeolite . The rare earth metal cations or elements may be faintly yellow or pink . It typically has a Mohs hardness of affixed to the zeolite in any reasonable chemical or physical 1-10 , preferably 2-8 , preferably 4-6 , or about 5 and a density manner, such as affixed to one or more surfaces of the of 1.5-3.0 g/ cm ", preferably 1.75-2.5 g /cm ", preferably zeolite , incorporated into the chemical framework of the 2.0-2.25 g / cm² or about 2.1 g/ cm². In cases where mordenite 5 zeolite , or alternatively , at least partially embedded within forms well developed crystals they are often hairlike ; very long , thin and delicate . Mordenite's molecular structure is a cavities and / or pore spaces of the zeolite . In a preferred framework containing chains of five membered rings of embodiment, the rare earth metal ions are incorporated into linked silicate and aluminate tetrahedral ( four oxygen atoms the chemical framework of the zeolite , preferably mordenite . arranged at the points of a triangular pyramid about a central 10 In certain embodiments , some of the Al atoms have been silicon or aluminum atom ) . Its framework is built on 5 -mem replaced by the rare earth metal element in the framework of bered rings arranged in columns parallel to the [001 ] axis . the zeolite . After impregnation with rare earth metal ions the Hence , the framework includes elliptical micropore (6-7x crystallinity of the zeolite , preferably mordenite , as well as 6.5-7.5 Å , preferably 6.7x7.0 Å ) tunnels parallel to the the crystal morphology of the zeolite, preferably mordenite C -axis and ( 2-3x5-6 Á , preferably 2.6x5.7 % ) tunnels parallel 15 is retained . In certain embodiments , scanning electron to the b -axis . By virtue of the small nature of the latter axis , microscopy (SEM ) analysis reveals several spots on the rare molecules are unable to pass through , and as such mordenite earth metal impregnated zeolite indicating the binding is generally regarded as a one -dimensional zeolite . Morden between the zeolite crystal and the impregnated rare earth ite's high ratio of silicon to aluminum atoms makes it metals (FIG . 37 through FIG . 42 ) . In certain embodiments , relatively more resistant to attack by acids than many other 20 introduction of rare earth elements into a zeolite framework zeolites . Mordenite is one of the most abundant zeolites in tends to alter the Lewis acid sites in the framework and can altered volcanic deposits ; it is found in volcanic rock such as be used to adjust the amount and intensity of distribution of rhyolite , andesite , and basalt. Itmay be associated with other the acid sites. This may be attributed to the formation of zeolites such as stilbite and heulandite . hydroxyl rare earth cation species in zeolite channels which In a preferred embodiment , the zeolite of the zeolite 25 helps stabilize the zeolite framework . impregnated with a rare earth metal is a mordenite zeolite . As used herein , a rare earth metal or rare earth element In a preferred embodiment, the zeolite of the zeolite impreg may refer to any member of the lanthanide series ( lantha nated with a rare earth metal is a mordenite zeolite , prefer num , cerium , praseodymium , neodymium , promethium , ably having the molar composition Na O : A1,0230Si02: samarium , europium , gadolinium , terbium , dysprosium , hol 780H20 , which has a silica to alumina molar ratio (Si /Al ) in 30 mium , erbium , thulium , ytterbium , lutetium ), the actinide the range of 5 to 40 , preferably 6 to 35 , preferably 7 to 30 , series (actinium , thorium , protactinium , uranium , neptu preferably 8 to 25 , preferably 9 to 22, more preferably 10 to nium , plutonium , americium , curium , berkelium , califor 20 , more preferably 12 to 18 , more preferably 14 16 , or nium , einsteinium , fermium , mendelevium , nobelium , law suitableabout 15. including Several morphologies, but not limited of tothe spherical mordenite, circular zeolite pieare , 35 rencium ), as well as scandium , yttrium and mixtures thereof . flat prismic , ellipsoidal, hexagonal star - like prism , and the As used herein , the terms rare earth (RE ), rare earth element like. In a preferred embodiment , the zeolite of the zeolite (REE ) , rare earth metal (REM ), rare earth oxides (REO ), impregnated with a rare earth metal is a mordenite zeolite rare earth elements and yttrium (REY ) , light rare earth which has a flat prismic crystal with an average crystal size elements (LREE , Sc, La , Ce , Pr, Nd , Pm , Sm , Eu , and Gd ; estimated using the Scherer equation and defined as an 40 also known as the cerium group ), and heavy rare earth average crystal dimension perpendicular to the reflection elements ( Y , Tb , Dy, Ho , Er, Tm , Yb , and Lu ; also known as plane, of 2-15 um , preferably 2.5-12 um , preferably 3-10 the yttrium group ) are used synonymously . In a preferred um , preferably 4-9.5 um , preferably 5.5-8 um , preferably 6-7 embodiment, the rare earth metal is at least one selected um . from the group consisting of lanthanum and cerium . It is In certain embodiments , the zeolite of the zeolite impreg- 45 equally envisaged that any rare earth metal as described nated with a rare earth metal is a mordenite zeolite and is herein may be employed in addition to , or in lieu , of prepared by a sol- gel method . Sol- gel processing refers to a lanthanum and / or cerium . process of slow crystallization of a silica -alumina gel in the In a preferred embodiment, the zeolite impregnated with presence of alkalis and / or organic templates. The product the rare earth metal has a weight percentage of the rare earth properties depend on the reaction mixture composition , pH 50 metal in the range of 1-15 wt % relative to the total weight of the system , operating temperature , pre- reaction “ seeding of the zeolite impregnated with the rare earth metal, pref time” reaction time as well as templates used . The silicate erably 1.5-12 wt % preferably 2-10 wt % , preferably 4-9 wt sol formed by the hydrothermal method is very stable . The % , preferably 5-8 wt % relative to the total weight of the method of preparation of the mordenite zeolite is not viewed zeolite impregnated with the rare earth metal . In certain as particularly limiting . The method of preparation of the 55 embodiments , the zeolite is mordenite and the rare earth rare earth metal impregnated zeolite is not viewed as par metal is lanthanum and the mordenite zeolite impregnated ticularly limiting . These methods should be known to those with lanthanum has a weight percentage of lanthanum in the of ordinary skill in the art . range of 1-15 wt % relative to the total weight of the In a preferred embodiment, the electrode of the present mordenite zeolite impregnated with lanthanum , preferably disclosure comprises a zeolite , preferably mordenite impreg- 60 1.25-10 wt % , preferably 1.5-5 wt % , preferably 1.75-3 wt nated with a rare earth metal, preferably cerium and /or % , or about 2 wt % relative to the total weight of the lanthanum . As used herein , " impregnated " , " incorporated " mordenite zeolite impregnated with lanthanum . In certain or “ exchanged” describes being completely or partially filled embodiments , the zeolite is mordenite and the rare earth throughout, permeated , and /or infused . The rare earth metal metal is cerium and the mordenite zeolite impregnated with elements or cations may be affixed inside of and / or on an 65 cerium has a weight percentage of cerium in the range of outer surface of the zeolite . The rare earth metal cations or 1-15 wt % relative to the total weight of the mordenite elements may be affixed on one or more surfaces of the zeolite impregnated with cerium , preferably 4-14 wt % , US 10,495,601 B2 29 30 preferably 6-13 wt % , preferably 8-12 wt % , or about 10 wt enzymes (oxidases , dehydrogenases , hydrolases, auxiliary % relative to the total weight of the mordenite zeolite enzymes) , nucleic acids , immunosensors , tissues , cells , and impregnated with cerium . other biomolecules . In a preferred embodiment, the electrode of the present According to a second aspect , the present disclosure disclosure has a weight percentage of the zeolite impreg- 5 relates to a method for detecting and quantifying a heavy nated with the rare earth metal in the range of 1-30 % relative metal ion in an aqueous solution comprising: i) contacting to the total weight of the electrode , preferably 2-25 % by the aqueous solution with the electrode in any of its embodi weight, preferably 3-20 % by weight, preferably 4-15 % by ments , ii) generating a negative deposition potential at the weight, preferably 5-10 % by weight, or about 5 % by weight electrode to reduce the heavy metal ion and form a reduced relative to the total weight of the electrode . 10 heavy metal that is deposited onto the electrode , iii ) scan The construction of the actual physical electrode and ning a potential range from the negative deposition potential holders or housings is not viewed as particularly limiting . in the positive direction at the electrode to oxidize and strip Exemplary holders and / or housings include , but are not the reduced heavy metal from the electrode , and iv ) mea limited to tubings and rods (plugs ) with hollow ends, rotated suring the current during the scanning . In general, the rare disc electrodes , piston - driven electrode holders , and a vari- 15 earth metal impregnated zeolite modified electrode in any of ety of commercially available electrode holders. In certain its embodiments is contacted with an aqueous sample and in embodiments , the electrode material (i.e the electrode) in the electrical communication with a reference electrode . A form of a paste may be packed into a plastic micropipette tip potential is applied between the reference electrode and the ( 10-100 mm long , preferably 20-75 mm long , preferably rare earth metal impregnated zeolite modified electrode 30-50 mm long , or about 40 mm long an 0.01-1.0 mm in 20 produce a current. Changes in the current as a result of diameter, preferably 0.05-0.5 mm in diameter, or about 0.01 reduction / oxidation/ decomposition of detected analytes (i.e. mm in diameter ). The working electrode held or housed in heavy metal ions) can be used to determine the amount of this manner may further comprise an electrical contact , such the analyte in the sample into which the electrode is placed . as for example a copper wire (FIG . 9 ). A variety of opera Non - limiting examples of aqueous solutions ( i.e. heavy tional set ups for the electrode are well known to those of 25 metal contaminated and / or Cd ( II )/ Pb ( II) contaminated aque ordinary skill in the art . ous solutions ) , water sources and systems include, but are In a preferred embodiment, the rare earth impregnated not limited to , surface water that collects on the ground or zeolite modified electrode of the present disclosure in any of in a stream , aquifer , river, lake, reservoir or ocean , ground its embodiments has a greater electroactive surface area water that is obtained by drilling wells , run -off , industrial relative to a substantially similar electrode lacking the 30 water, public water storage towers, public recreational pools zeolite impregnated with the rare earth metal, such as an and / or bottled water. Methods for the detection and quanti electrode comprising a substantially similar zeolite free of fication of heavy metals in aqueous solutions according to rare earth metal exchange or incorporation . In a preferred the present disclosure include contacting the rare earth metal embodiment, the rare earth impregnated zeolite modified impregnated zeolite modified electrode of the present dis electrode of the present disclosure in any of its embodiments 35 closure in any of its embodiments with heavy metal con has a 10-40 % greater electroactive surface area relative to a taminated water sources and systems. The methods may be substantially similar electrode lacking the zeolite impreg carried out in tanks , containers , or small scale applications nated with the rare earth metal, preferably 15-35 % , prefer in both batch mode and fixed -bed or column mode . In a ably 20-30 % greater electroactive surface area relative to a preferred embodiment, the aqueous solution comprises substantially similar electrode lacking the zeolite impreg- 40 greater than 80 % v /v of water , preferably greater than 85 % nated with the rare earth metal. In a preferred embodiment, V /v water , preferably greater than 90 % v /v water, preferably the rare earth impregnated zeolite modified electrode of the greater than 95 % v / v water , preferably greater than 99 % V / v present disclosure in any of its embodiments has an elec water . troactive surface area of greater than 5 mm², preferably In a preferred embodiment, the rare earth metal impreg greater than 10 mm², preferably greater than 15 mm², 45 nated zeolite modified electrode of the present disclosure in preferably greater than 20 mm², preferably greater than 22 any of its embodiments may be utilized to detect analytes . mm², preferably greater than 24 mm², preferably greater As used herein , the term “ analyte” refers to a substance that than 26 mm ’, preferably greater than 28 mm ’, preferably is (or whose chemical constituents are) being identified , greater than 30 mm², preferably greater than 35 mm ?, detected , and /or measured by the rare earth metal impreg preferably greater than 40 mm², preferably greater than 50 50 nated zeolite modified electrode described herein . An ana mm . lyte may be a component of a fluid (i.e. vapor or liquid ) It is equally envisaged that the rare earth metal impreg sample in which the rare earth metal impregnated zeolite nated zeolite modified electrode of the present disclosure in modified electrode is immersed or contacted with . The any of its embodiments may be further modified in addition analyte may be various organic ( i.e. uric acid and biologi to zeolite impregnation . Additional suitable chemical modi- 55 cally important catecholamines ) and inorganic species ( i.e. fications include , but are not limited to intrinsic modifica toxic metals ), preferably metal ions, more preferably heavy tion , extrinsic modification ( surface modification and bulk metal ions, in various matrices. In one embodiment , the modification , chemical modifiers including , but not limited aqueous solution is an environmental sample such as for to , inorganic materials (Prussian -blue derivatives, polyoxo example drinking water and the analyte is a heavy metal ion metallates , clays , zeolites , molecular sieves, metal oxides 60 and the electrodes described herein display a lack of toxicity and sol- gel derived inorganic materials ), organic and orga compared to traditional mercury electrodes. In a preferred nometallic compounds ( organic ligands, organic catalysts , embodiment, the aqueous solution has an initial analyte organometallic complexes , surfactants , amphiphilic modifi concentration of 10-3 to 10-12 M , preferably 10-4 to 10-10 ers , lipophilic modifiers , organic polymers and macromol M , preferably 10-8 to 10-9 M , or alternatively 1-1000 ppb , ecules ), organic - inorganic hybrid materials , nanomaterials , 65 preferably 5-500 ppb , preferably 50-250 ppb . surface treatments , coatings, and alterations. Additional suit The metal ions that are detected and/ or quantified are able biological modifications include , but are not limited to , preferably heavy metal ions. In a preferred embodiment, a US 10,495,601 B2 31 32 heavy metal ion has a density of greater than 3.5 g / cm3 dized at the electrode. The resultant current is proportional and / or an atomic weight of greater than 20. Exemplary metal to the concentration of the chemical species . Stripping ions that can be detected and /or quantified by the electrode voltammetry is a two -step technique in which the first step and method of the present disclosure in any of their embodi consists of the electrolytic deposition of a chemical species ments are of a wide range and include, but are not limited to 5 or analyte onto an inert electrode surface at a constant ions of Ag , Ca, K , Zn , Na, Pb , Mn, Fe, Co , Ni, Al, Cu , Sn , potential. This preconcentration step can involve either an Cd, Hg, Cr, Fe, Bi, Ga, Ge, Au, In , TI, Rb, Cs, As, Sb , Cr, anodic or cathodic process . The most common use of Zn , V , Pt, Pd , Rh , and mixtures thereof. Further , these metal stripping voltammetry involves a anodic and / or cathodic ions may be of any oxidation state M + 1 , M + 2 , M + 3 , etc. In a process in which a metal ionic species is reduced from the preferred embodiment, the heavy metal is at least one 10 solution onto an electrode . The second step consists of the selected from the group consisting of Co , Cu , Zn , Hg, As, Sr, application of a voltage scan to the electrode that causes an Mo, Cd , and Pb , most preferably the heavy metal ion is at electrolytic dissolution , or “ stripping ” , of the various species least one selected from the group consisting of lead ( II ) , Pb deposited at the electrode back into solution at characteristic ( II ) and cadmium (II ) , Cd ( II ). It is equally envisaged that the potentials . rare earth metal impregnated zeolite modified carbon paste 15 The remarkable sensitivity of stripping voltammetry is electrode may be adapted or chemically modified to detect attributable to the preconcentration that takes place during and / or quantify one ormore additional metal ions in addition deposition . For preconcentration to take place , the deposited to , or in lieu of lead ( II ) and cadmium ( II ) . In one embodi material must adhere to the electrode surface, stripping ment, the additional metal ion may be any ion which is voltammetry can be used to determine those chemical spe detected and / or quantified selectively or collectively by the 20 cies that will be retained by the electrode. Stripping volta electrode in any of its embodiments . Exemplary additional mmetry is primarily a trace analytical technique. It can be metal ions include, but are not limited to , an alkali metal (Li , used to make routine analytical determination at the sub Na, K , etc. ), an alkaline earth metal (Mg . Ca, Sr, etc. ) a ppm level . In a preferred embodiment, the method is an lanthanide metal (La , Ce , Eu , Yb , etc.) , an actinide metal anodic stripping voltammetry ( ASV ) method . As used ( Ac , Th , etc. ), or a post - transition metal ( A1, Sn , Pb , In , etc. ). 25 herein anodic stripping voltammetry is a voltammetric Preferably the additional metal ion is a transition metal ion , method for quantitative determination of specific ionic spe preferably a heavy metal ion . Exemplary additional transi cies . Anodic stripping voltammetry is used to determine the tion metals of the metal ion include, but are not limited to , concentration of trace metals . The analyte of interest (i.e. Sc , Ti, Cr, Mn, Fe, Co , Ni, Cu, Zn, Y , Zr, Pd , Ag, W , Os, Au , one or more heavy metal ions in an aqueous solution ) is and Hg. 30 contacted with the electrode of the present disclosure in any In preferred embodiments , the method can be described as of its embodiments , the analyte of interest is electroplated on voltammetric or as a voltammetry method . As used herein , the working electrode during a deposition (or accumulation ) voltammetry refers a category of electroanalytical meth step , and oxidized from the electrode during a stripping step . ods used in analytical chemistry and various industrial Anodic stripping voltammetry consists of a deposition processes . In voltammetry , information about an analyte (i.e. 35 potential that is more negative than the half- wave potential a heavy metal ion ) is obtained by measuring the current as of the analytes or metals to be determined and an anodic the potential is varied . In general, voltammetry experiments (positive going) scan to oxidize the reduced analyte or metal or voltammetry methods investigate the half- cell reactivity back into solution . The current is measured during the of an analyte . Voltammetry is a study of current as a function stripping step . The oxidation of a species is registered as a of applied potential. The corresponding curves ( I = f ( E ) ) are 40 peak in the current signal at the potential at which the referred to as voltammograms. The potential may be varied species begins to be oxidized . The stripping step can be arbitrarily step by step or continuously , and the actual either linear, staircase , squarewave, or pulse . In certain current value is measured as the dependent variable . The embodiments , it is equally envisaged that the working opposite ( i.e. amperometry ) is also possible but uncommon . electrode or method of the present disclosure may be The shape of the voltammogram curves depends on the 45 adapted to a cathodic stripping voltammetry ( CSV ) method speed of the potential variation (nature of driving force ) and wherein a relatively positive potential is applied during the on whether the solution is stirred or quiescent (mass trans deposition and stripping consists of a cathodic (negative fer ). Most experiments and methods control the potential going ) to reduce the analyte back into solution . Exemplary ( volts ) of an electrode in contact with the analyte while analytes detected by cathodic stripping voltammetry measuring the resulting current (amperes ) . Exemplary vol- 50 include , but are not limited to arsenic , chloride , bromide , tammetric methods that may characterize the method of the iodide, selenium (IV ) , sulfide, mercaptans (RSH ) , thiocya present disclosure in any of its embodiments , often in terms nate (SCN ) , and thio compounds. of applied waveform of the applied biasing potential This type of method or experiment generally requires at include, but are not limited to , linear sweep voltammetry , least two electrodes to perform . The working electrode , staircase voltammetry , squarewave voltammetry , cyclic vol- 55 which makes contact with the analyte , must apply the tammetry, anodic stripping voltammetry, cathodic stripping desired potential in a controlled way and facilitate the voltammetry, adsorptive stripping voltammetry , alternating transfer of charge to and from the analyte . In a preferred current voltammetry , polarography, rotated electrode volta embodiment, the working electrode is the rare earth impreg mmetry , normal pulse voltammetry , differential pulse volta nated zeolite modified carbon paste electrode (RE -ZMCPE ) mmetry , chronoamperometry , and the like. In a preferred 60 described herein in any of its embodiments . A second embodiment, the method of the present disclosure is a electrode, or counter electrode, acts as the other half of the stripping voltammetry method , most preferably an anodic cell . This second electrode, or counter electrode , must have stripping voltammetry method . a known potential with which to gauge the potential of the Voltammetry is an electrochemical technique in which the working electrode, furthermore it must balance the charge current- potential behavior at an electrode surface is mea- 65 added or removed by the working electrode. While this is a sured . The potential is varied in a systematic manner to viable setup it suffers from it being difficult for a single cause electroactive chemical species to be reduced or oxi electrode to maintain a constant potential while passing US 10,495,601 B2 33 34 current to counter redox events at the working electrode . In solution selected from the group consisting of citrate buffer , a solution to this problem , the roles of supplying electrons phthalate buffer , acetate buffer, phosphate buffer , and sul and providing a reference potential are divided between two phate buffer , more preferably phosphate buffer . In a pre separate electrodes . Anodic stripping voltammetry generally ferred embodiment , the concentration of the buffer in the incorporates three electrodes, a working electrode, an aux 5 aqueous solution may range from 0.01-1.0 M , preferably iliary electrode (also referred to as a counter electrode ) and 0.01-0.5 M , preferably 0.05-0.25 M , preferably 0.08-0.2 M , a reference electrode . The reference electrode is a half cell or about 0.1 M. In a preferred embodiment, the aqueous with a known reduction potential . Its only role is to act as sample has a pH in the range of 3-5 , preferably 3.2-4.8 , reference in measuring and controlling the working elec preferably 3.4-4.6 , preferably 3.5-4.5 , preferably 3.6-4.4 , trode's potential and at no pointdoes it pass any current. The 10 preferably 3.8-4.2 or about 4.0 . auxiliary ( second or counter ) electrode passes all the current In one step of the method for detecting and quantifying a needed to balance the current observed at the working heavy metal ion in an aqueous solution , the aqueous solution electrode . In order to achieve this current , the auxiliary is contacted with the rare earth metal impregnated zeolite electrode will often swing to extreme potentials at the edges modified electrode of the present disclosure in any of its of the solvent window , where it oxidizes or reduces the 15 embodiments . Preferably at least one end of the electrode is solvent or supporting electrolyte . These electrodes the work in contact with the aqueous solution or sample , preferably ing, reference, and auxiliary make up the modern three the length of the electrode material immersed in the aqueous electrode system . In a preferred embodiment , the method is solution may range from 10-100 mm , preferably 20-80 mm , performed in a three electrode system , comprising a working preferably 30-70 mm , preferably 40-60 mm . In certain electrode , an auxiliary (or counter ) electrode and a reference 20 embodiments , the method may further comprise a deaerating electrode. step subsequent to the contacting wherein the aqueous In a preferred embodiment, the rare earth impregnated solution is purged for 1-15 minutes , preferably 2-10 minutes zeolite modified carbon paste electrode (RE - ZMCPE ) with a purified inert gas ( i.e. nitrogen , argon ) to eliminate described herein in any of its embodiments functions as a interferences from oxygen . Optionally the inert gas may be working electrode. The auxiliary or counter electrode is not 25 passed through a scrubbing tower filled with supporting viewed as particularly limiting as long as it does not react electrolyte in order to allow the nitrogen stream to be with the bulk of the analyte solution and conducts well. In saturated with the electrolyte solution to eliminate the pos a preferred embodiment, the counter electrode comprises or sibility of pH changes or volatilization in the cell. In certain is fabricated from electrochemically inert materials includ embodiments , the method may further comprise a condi ing , but not limited to , platinum , gold or carbon , in a most 30 tioning or cleaning step subsequent to the deaerating. As preferred embodiment the counter electrode is a platinum used herein , conditioning is a term that denotes electrolytic wire . In another embodiment, the counter or auxiliary elec cleaning of the electrode surface . A specified potential, trode may be isolated from the working electrode, such as by preferably a more oxidizing potential than the analyte of means of a glass flit . Such isolation prevents any byproducts interest, is applied to the electrode for a controlled time in generated at the auxiliary electrode from contaminating the 35 order to remove contaminants or materials not removed main test solution . The reference electrode is preferably an during a stripping step from the electrode . In certain embodi aqueous electrode . Exemplary reference electrodes include, ments , conditioning is not required with the electrode of the but are not limited to , a standard hydrogen electrode (SHE ), present disclosure as a new electrode is fabricated for each a normal hydrogen electrode ( NHE ), a reversible hydrogen determination or analysis . In contrast, conditioning may be electrode (RHE ) , a saturated calomel electrode (SCE ), a 40 a necessity when the same electrode surface is used in copper - copper( II ) sulfate electrode ( CSE ), a silver chloride subsequent determinations or analyses. In embodiments (Ag / AgCl ) electrode, a pH buffered solution pH electrode, a where the electrode is used to detect and quantify metals , the palladium -hydrogen electrode , a dynamic hydrogen elec conditioning potential should be positive with respect to the trode (DHE ) , a mercury -mercurrous sulfate electrode half -wave potential of the analyte to ensure the oxidation of (MSE ), and the like . In a most preferred embodiment , the 45 metals back into solution . In a preferred embodiment, the reference electrode is a silver chloride (Ag / AgCl) electrode . conditioning potential is greater than -0.5 V , preferably In certain embodiments , the aqueous solution may further greater than -0.4 V , preferably greater than -0.3 V , prefer comprise a supporting electrolyte . As used herein , a sup ably greater than -0.2 V, preferably greater than 0.1 V, porting electrolyte in electrochemistry refers to an electro preferably greater than 0.0 V and is generally suitable for lyte containing chemical species that are not electroactive 50 removing any such contaminants without affecting the elec (within the range of potentials used ). Supporting electrolytes trode. The solution is optionally stirred during conditioning , are widely used in electrochemical measurements when preferably stirred, and in preferred embodiments the condi control of electrode potentials is required . This may increase tioning time is 10-360 seconds, preferably 20-240 seconds, the conductivity of the solution , eliminate the transport of preferably 30-180 seconds, preferably 60-120 seconds. electroactive species by ion migration in the electric field , 55 In one step of the method for detecting and quantifying a maintain constant ionic strength or maintain constant pH . In heavy metal ion in an aqueous solution , a negative deposi a preferred embodiment, the aqueous solution further com tion potential is generated at the rare earth metal impreg prises a buffer solution as a supporting electrolyte . As used nated zeolite modified electrode of the present disclosure in herein , a buffer solution (more precisely , pH buffer or any of its embodiments to reduce the heavy metal ion and hydrogen ion buffer ) refers to an aqueous solution consisting 60 form a reduced heavy metal that is deposited onto the of a mixture of a weak acid and its conjugate base , or vice electrode . Briefly , the potential is held at a lowered potential , versa . Its pH changes very little when a small or moderate low enough to reduce the analyte and deposit it on the amount of strong acid or base is added to it and thus it is used electrode . to prevent changes in the pH of a solution . Buffer solutions In the deposition step , the deposition potential is applied are used as a means of keeping pH at a nearly constant value 65 to the working electrode (i.e. the rare earth metal impreg in a wide variety of chemical applications. In certain nated zeolite modified electrode ) to cause the material of embodiments , the aqueous sample further comprises a buffer interest to be deposited onto the surface of the working US 10,495,601 B2 35 36 electrode. The solution is optionally and preferably stirred measured current at these potentials is proportional to the during deposition to maximize analyte - electrode contact , concentration of the analyte in the original sample . Increases preferably stirred at 100-1000 rpm , preferably 200-800 rpm , in sensitivity may be noted for different waveforms of the preferably 400-700 rpm , or about 600 rpm . Generally , the biasing or striping potential, the biasing or stripping poten selection of the deposition potential depends upon whether 5 tial may have a waveform of linear voltammetry, linear the material to be determined is oxidized or reduced . For a sweep voltammetry, square wave voltammetry, cyclic vol reducible metal, the deposition potential should be negative tammetry, or pulse voltammetry . In a preferred embodiment, with respect to the half -potential of the metal . In contrast, for the scanning and the measuring are performed with square oxidizable materials , the deposition potential should be wave voltammetry and the biasing potential or stripping selected such that it is positive with respect to the half -wave 10 potential has the waveform of square wave voltammetry . In potential. The choice of the deposition potential can provide a preferred embodiment, the waveform has amplitude rang some selectivity in the measurement. For example , a dc ing from 0.01-1.0V , preferably 0.05-0.5 V , preferably 0.08 polarogram of lead and cadmium shows a first plateau as the 0.4 V, preferably 0.1-0.35 V , preferably 0.15-0.3 V and the diffusion - limited current due to the reduction of lead and a waveform has a frequency of 1-150 Hz , preferably 5-100 second plateau due to the diffusion -limited current of both 15 Hz, preferably 10-80 Hz, preferably 15-60 Hz, preferably lead and cadmium . Deposition at a certain potential may 20-50 Hz. In a preferred embodiment, the stripping is only yield a stripping peak for lead . There is no contribution performed without stripping . A slow ( 2-5 mV /sec ) or a more to the stripping voltammogram from the cadmium also rapid ( 10-100 mV /sec ) scan rate may be applied to the present in solution since deposition at this potential reduces electrode . In a preferred embodiment, the scanning is per lead only . Deposition at a more negative potential yields a 20 formed at a scan rate of 2-500 mV/ s , preferably 5-400 mV/ s , somewhat higher stripping peak still with no contribution preferably 10-350 mV /s , preferably 15-300 mV/ s , prefer from cadmium . Deposition at an even more negative poten ably 20-250 mV / s , preferably 25-200 mV / s , preferably tial (more negative than -0.6 V ) yields two stripping peaks 50-150 mV/ s . The scanning range must span the potential since deposition at this potential is negative enough to region where the chemical specie ( s ) of interest are electro reduce cadmium and lead simultaneously . In this manner, 25 lyzed back into solution and the current of peaks corre multiple heavy metal ions, 2-12 , preferably 2-8 , preferably sponding to the analytes that are present are measured , thus 2-6 , preferably 2-3 may be simultaneously detected and /or each metal phase species is selectively oxidized during the quantified . In a preferred embodiment, the deposition poten anodic potential sweep , such as for example -2.0 to 0.0 V , tial is negative , and the negative deposition potential is in the preferably -1.8 to 0.0 V , preferably -1.6 to 0.0 V , preferably range of -2.0 V to -0.2 V , preferably -1.8 V to -0.4 V, 30 -1.4 to 0.0 V. preferably -1.6 V to -0.6 V, preferably -1.5 V to -0.8 V , In certain embodiments , the rare earth metal impregnated preferably -1.4 V to -1.0 V , preferably -1.3 V to -1.1 V , or zeolite modified electrode of the present disclosure in any of about -1.2 V. its embodiments is not reused and a new electrode is The deposition time is an important experimental param fabricated for each determination or analysis . In certain eter that is unique to stripping voltammetry . If more sensi- 35 embodiments , the rare earth metal impregnated zeolite tivity is required, an analyst may increase the deposition modified electrode of the present disclosure in any of its time. This increases the degree of preconcentration , making embodiments may be reusable and may be capable of a greater amount of deposited analyte available at the repeated detection without calibration or replacement. In electrode during the stripping step . In a preferred embodi certain embodiments , the electrode may be polished before ment, the reduced heavy metal is deposited over a time 40 immersion in the aqueous solution or reuse , such as for period ( i.e. the deposition time) in the range of 10-250 example with alumina particles with a size ranging from seconds, preferably 15-225 seconds, preferably 20-200 sec 0.05-0.5 um , preferably 0.1-0.5 um , more preferably 0.2-0.3 onds , preferably 30-180 seconds , preferably 50-175 sec um . The electrode may further be rinsed with solvents before onds, preferably 75-150 seconds, preferably 100-140 sec immersion in the aqueous solution or reuse such as for onds, preferably 110-125 seconds, or about 120 seconds. In 45 example ethanol, acetone, and water to remove impurities . certain embodiments , this deposition step may further com In one or more embodiments , the heavy metal ion detec prise an equilibration period . During equilibration , the depo tion and quantification method described herein may further sition potential is applied to the working electrode , but comprise and / or be preceded by calibration procedures with stirring is halted . This may allow convection currents from steps including measuring the voltammogram of a plurality the stirring to decrease to a negligible level and also allow 50 of calibration samples comprising a series of known time for the deposited material to stabilize . In a preferred amounts of the analyte or heavy metal ion in the same embodiment, the equilibration time is 1-120 seconds, pref medium as the aqueous solution to be tested , in order to erably 10-60 seconds, preferably 20-40 seconds, or about 30 obtain a calibration curve for the rare earth metal impreg seconds . nated zeolite modified electrode. In a preferred embodiment, In one step of the method for detecting and quantifying a 55 the calibration is performed over two concentration ranges heavy metal ion in an aqueous solution , a potential range is of the analyte , such as for example 50-500 ppb and 5-50 ppb . scanned from the negative deposition potential in the posi Preferably , the square wave stripping voltammetry shows a tive direction at the rare earth metal impregnated zeolite linear relationship between the stripping current and the modified electrode of the present disclosure in any of its concentration of the analyte or heavy metal ion . In a embodiments to oxidize and strip the reduced heavy metal 60 preferred embodiment the concentration limits of detection from the electrode and the current is measured during the for many metals is in the low ppb to high ppt range ( S / N = 3 ) scanning and compares favorably with atomic absorption spectros In the stripping step , an excitation waveform is applied copy (AAS ) or inductively coupled plasma ( ICP ) analysis In which electrolyzes the deposited material back into the a preferred embodiment the method and the rare earth metal solution . The current is then measured versus the applied 65 impregnated zeolite modified electrode has a limit of detec potential. The materials deposited at the electrode will strip tion in the range of 0.005-0.5 ug L - 1, preferably 0.01-0.45 at potentials very close to their half -wave potentials . The ug L-?, preferably 0.02-0.4 ug L - 1, preferably 0.03-0.35 ug US 10,495,601 B2 37 38 L - 1, preferably 0.035-0.3 ug L - 1, preferably 0.05-0.25 ug most preferably a Pb ( II ) and /or Cd ( II ) heavy metal ion into L- , preferably 0.10-0.20 ug L - 1 . In a preferred embodiment contact with the electrode of the present disclosure in any of the method and the rare earth metal impregnated zeolite its embodiments for sensing . modified electrode has a limit of quantitation in the range of In certain embodiments , the sensing device may be in 1-15 ug L - 1 , preferably 2-12 ug L - 1, preferably 3-10 ug L - 1, 5 communication with at least one readout device that may preferably 3.5-8 ug L- , preferably 4-6 ug L generally be capable of measuring the current and / or poten In a preferred embodiment, the rare earth metal is lan tial at the electrode of the present disclosure in any of its thanum and the heavy metal ion is Pb ( II ), and the method embodiments . In most preferred embodiments , the readout has a Pb ( II ) detection limit in the range of 0.15-0.30 ug L - 1 , device may be a set of electronics . An electronic readout preferably 0.18-0.28 ug L - 1, preferably 0.20-0.25 ug L - 1 , 10 device , for example, may be capable of detecting current preferably 0.21-0.24 ug L- ?, or about 0.225 ug L - 1 . In a changes . Moreover , the readout device may be a component preferred embodiment, the rare earth metal is lanthanum and of the sensing device or may be remotely separated from the the heavy metal ion is Cd (II ), and the method has a Cd ( II ) sensing device . Furthermore , the readout device may also be detection limit in the range of 0.05-0.20 ug L- 1 , preferably linked to an adapter that can interface with a controller 0.08-0.18 ug L- ?, preferably 0.10-0.15 ug L-?, preferably 15 device . Preferably , a readout circuit is employed to enable 0.11-0.14 ug L - 1 , or about 0.122 ug L-?. In a preferred determination of the presence and /or amount of an analyte , embodiment, the rare earth metal is cerium and the heavy preferably a heavy metal ion , and may form part of the metal ion is Pb ( II ) , and the method has a Pb ( II ) detection readout device . limit in the range of 0.02-0.15 ug L- , preferably 0.04-0.12 20 In certain embodiments , the readout circuit may be con ug L - 1 , preferably 0.05-0.10 ug L - 1 , preferably 0.06-0.08 ug figured to measure the current and /or the potential at the rare L - 1, or about 0.07 ug L - 1 . In a preferred embodiment, the earth metal impregnated zeolite described herein . Further, rare earth metal is cerium and the heavy metal ion is Cd ( II ), the readout circuit may also be configured to indicate the and the method has a Cd (II ) detection limit in the range of current and /or potential value ( s ) to a user of the sensing 0.01-0.10 ug L- ?, preferably 0.02-0.08 ug L - 1, preferably 25 device such that said user can detect the presence of the 0.03-0.07 ug L-' , preferably 0.04-0.06 ug L-' , preferably analyte , preferably a heavy metal ion , and quantify it based on this measurement. In certain embodiments , to achieve 0.04-0.05 ug L - 1 , or about 0.046 ug L - 1 . this , the readout circuit may comprise an electronic display In addition to the sensitivity of the method is preferably and / or loudspeaker or other interface for presenting the highly reproducible . As used herein , relative standard devia 30 current and / or potential value( s ) to the user , and may further tion (RSD ) or coefficient of variation (CV ) refers to a comprise a transmitter and/ or transceiver for transmitting the standardized measure of dispersion of a probability distri data to another device . This latter feature is envisaged to bution or frequency distribution . It is often expressed as a enable the user to monitor the environment from a ren te percentage , and is defined as the ratio of the standard location . In another embodiment, the readout circuit may be deviation to the mean (or its absolute value ) . The CV or RSD 35 configured to determine the presence and / or amount of is widely used in analytical chemistry to express the preci analyte , preferably a heavy metal ion , using the current sion and repeatability of an assay , technique, or method . In and /or potential value ( s ) and indicate the result to the user, a preferred embodiment, the method of the present disclo with or without the current and /or potential value( s ). In such sure in any of its embodiments and the rare earth metal embodiments , the user is provided with the end result impregnated zeolite modified electrode of the present dis- 40 without requiring derivation from the raw data . closure in any of its embodiments has a reproducibility as In certain embodiments , the practice of this analysis may measured by a relative standard deviation in the range of be performed by a processor in combination with a storage 1-5 % , preferably 1.5-4 % , preferably 1.75-3.5 % , preferably medium . For example , a processor may be configured to 2-3 % , preferably 2.2-3.8 % . receive the current and /or potential value( s ) from the readout According to another aspect , the present disclosure relates 45 circuit and compare this with predetermined calibration data to a sensing device . The electrode of the present disclosure ( i.e. predetermined measurements of current and / or potential described herein in any of its embodiments may be part of difference versus analyte concentration ) from the storage ( i.e. integrated in ) the sensing device which may further medium to determine the presence and / or amount of anal comprise an aforementioned reference electrode, counter ayte . electrode , or both . A number of voltammetric systems are 50 It is equally envisaged that the method , detectors and produced commercially for the determination of specific sensors described herein may be adapted to a variety of species that are of interest in industry and research . Although electroanalysis , including , but not limited to , the determi these devices may sometimes be called electrodes , they are nation of inorganic ions , complex species, and molecules in fact more often complete voltammetric cells that are including , but not limited to , noble metals , heavy metals , better referred to as sensors . These sensors or sensing 55 metalloids , metals of the iron , manganese , chromium , and devices can be employed for the analysis of various organic vanadium groups, platinum metals and uranium ,metal of the and inorganic analytes, preferably heavy metal ions, in fourth and third groups , metals of rare earths, metals of various matrices and may take the form of inexpensive and alkaline earths and alkaline metals , non -metallic ions, com field deployable instrumentation . The sensing device may plexes, and neutral molecules, the determination of organic also include a housing that comprises the electrode of the 60 substances and environmental pollutants , pharmaceutical present disclosure in any of its embodiments and a fluid and clinical analysis , and the determination of biologically distribution manifold that comprises a fluid flow path that is important compounds including , but not limited to alcohols , in fluid communication with the electrode of the present aldehydes, ketones and acids, amino compounds (i.e. disclosure in any of its embodiments , the counter electrode , amides, amines, amino acids ), antioxidants and phenolic and / or the reference electrode . In certain embodiments , the 65 compounds, carbohydrates and related compounds , coen fluid flow path can bring a fluid comprising at least one zymes , enzymes, proteins and related compounds, hor analyte , preferably a metal ion , preferably a heavy metal ion , mones, phytohormones and related compounds, purines , US 10,495,601 B2 39 40 pyridines , and pyrimidines, vitamins, and to employ whole ning (MAS ) , normal pulse voltammetry (NPV ) , nuclear cells , microorganisms, tissues, and tissue extracts as modi magnetic resonance spectrometry (NMR ), parts per million fiers . (ppm ), parts per billion (ppb ), rare earth (RE ) , revolutions The present embodiments are being described with ref per minute ( rpm ), square wave voltammetry ( SWV ) , scan erence to specific example embodiments included to illus- 5 ning electron microscopy (SEM ), square wave anodic strip trate not limit the scope of the invention . The examples ping voltammetry ( SWASV ) , working electrode (WE ) , below are intended to further illustrate methods protocols for X - ray diffraction spectrometry (XRD ), zeolite modified preparing and characterizing the rare earth metal impreg electrode (ZME ) , and zeolite modified carbon paste elec nated zeolite modified electrodes of the present disclosure . trode (ZMCPE ). Further , they are intended to illustrate assessing the proper 10 ties and applications of these electrodes . They are not Example 2 intended to limit the scope of the claims. General Fabrication of Prepared Electrodes Example 1 In one step themordenite zeolite (MOR ) was synthesized . 15 A gel having the molar composition 6Na20 : A1203: 30SiO2: General Materials and Methods of Characterization for 780H20 was synthesized according to the following proce Prepared Electrodes dure ; 2.10 g of NaOH was dissolved in 20 g of double All solvent and reagents used were of standard purity and deionized water (DDW ) . To this solution , 0.63 g of NaA102 of analytical grade. The chemicals include: NaOH ( PRS was added and the mixture was stirred until dissolution . codex , Panreac Qumica ), silica gel (pore size 60 Á , 70-230 20 Thereafter, 34.13 g of DDW was added while stirring . mesh , Sigma- Aldrich ), colloidal silica (LUDOS , 40 wt % , Finally , 6.95 g of SiO , was added and the mixture was Sigma -Aldrich ), sodium silicate (reagent grade , Lot: stirred for 1 hour (aging time) . The resulting gel was then MKBG3583 , Sigma - Aldrich ), fumed silica (175-225 m?/ g transferred to a Teflon - lined stainless steel autoclave and surface, 99.8 % , Sigma- Aldrich ) , NaAlO2 ( anhydrous, crystallization was carried out under hydrothermal condi Sigma- Aldrich ), NaH2PO4 and Na2HPO4 (fluka ), K4Fe 25 tions at 180 ° C. for 48 h . The material resulting after ( CN ) . (BDH chemicals ) , KCl ( anhydrous , Sigma- Aldrich ) , crystallization was centrifuged and washed with DDW until phosphoric acid (BDH , analar grade ), NH ,OH (Fisher sci the pH dropped below 9. The sample was allowed to dry entific ) , H2SO4 (Panreac Quimica ) , glacial acetic acid and overnight at room temperature in order to obtain the crystal ammonium acetate (Fisher scientific ). Solutions of Pb ( II ) powder. The crystal was calcined at 550 ° C. to expel all and Cd ( I ) were prepared from 1000 ppm stock solutions 30 organic matter present . The zeolite whose molar composi ( spectroscopic grade , BDH chemicals ). All solutions were tion was 6Na2O : A1,02: 30S102: 780H2O was characterized freshly prepared with double distilled water obtained from by X - ray diffraction (XRD ), scanning electron microscopy labstrong nanopure water distiller ( Thermoscientific ) . (SEM ) , energy - dispersive X - ray spectroscopy (EDX ) and Powder X - ray diffraction (XRD ) pattern of the crystalwas nuclear magnetic resonance (NMR ) . recorded on Rigaku miniflex II X -ray diffractometer using 35 This zeolite was further impregnated with rare earth Cuka radiation ( ? = 1.5418 Å ) with 20 from 50 to 50 ° and a metal. An appropriate amount of the metal precursors (La scanning step of 0.02. Morphology of the crystal was (NO3 ) 3.6H20 and / or Ce (NO3 ) 3.6H20 ) required to make 2 obtained by field emission scanning electron microscopy wt % , 5 wt % and 10 wt % of La and /or Ce impregnated (with FESEM gold ) LYRAprior to 3 analysisdual beam . Solid, Tescan state . Samples 27 A1 and were 29Si coated MAS 40 zeolites2 g of the was prepared dissolved mordenite in ethanol zeolite (40 underg ) and vigorous was mixed stirring with . NMR were carried out on a JEOL Lambda -500 Multi The resulting slurry was dried overnight in a fume hood and Nuclear Magnetic Resonance spectrometer with a solid state was later calcined at 550 ° C. for 4 h in static air ( temperature MAS probe . The 29Si MAS Spectra were taken at a pulse ramp 20 ° C./min ). The metal impregnated zeolite was used interval of 10 s with 20,000 scans per sample and a spin of in the fabrication of the final electrode . 4 kHz. The spectra were processed with 40 Hz line broad- 45 The zeolite modified carbon paste electrode ( ZMCPE ) ening and chemical shifts were determined relative to TMS was prepared by mixing an appropriate amount of graphite , as an external reference . Electrochemical experiments were zeolite and paraffin oil in order to form a paste according to performed on a CHI 760E electrochemical work station (CH various ratios as described below . The paste was packed into instruments , US) . An Ag/ AgCl electrode was used as refer the end of the tip of a micropipette ( 40 mm long , 0.1 mm in ence electrode and a platinum wire as the auxiliary elec- 50 diameter ) with copper wire as an electrical contact. The trode. The working electrode was a carbon paste electrode electrode was renewed after every experiment by packing in modified or unmodified with zeolite . a fresh paste and smoothening by polishing the surface on a The present disclosure will be better understood with weighing paper. Bare carbon paste electrode was prepared in reference to the following abbreviations: atomic absorption the same manner without the addition of zeolite (graphite spectrometry (AAS ), anodic stripping voltammetry (ASV ) , 55 and paraffin oil only ) and was used for comparison . FIG . 9 cyclic voltammetry ( CV ) , cathodic stripping voltammetry shows the finished composite electrode. (CSV ), chemically modified electrode (CME ) , differential pulse voltammetry (DPV ) , dropping mercury electrode Example 3 ( DME ), double deionized water (DDW ) , environmental protection agency (EPA ), energy dispersive X -ray spectrom- 60 Synthesis and Characterization of a Prepared Lanthanum etry (EDX ) , fluid catalytic cracking (FCC ) , graphite furnace Impregnated Zeolite Modified Carbon Paste Electrode (La atomic absorption spectrometry (GFAAS ), inductively ZMCPE ) coupled plasma optical emission spectrometry (ICP -OES ) , Mordenite with different silica to alumina ratios was inductively coupled plasma mass spectrometry ( ICP -MS ), synthesized hydrothermally in the absence of organic tem international zeolite association ( IZA ), linear sweep volta- 65 plate as previously described and investigated by X -ray mmetry (LSV ) , limit of detection (LOD ) , maximum con diffraction (XRD ) . The XRD pattern is shown in FIG . 10 . taminant level (MCL ) , mordenite (MOR ) , magic angle spin FIG . 10 shows the XRD patterns of samples synthesized US 10,495,601 B2 41 42 with silica to alumina ratios in the range of 10-30 , which Example 4 reveals that an amorphous material was obtained for the sample with a silica to alumina ratio of 10 ( a ), while the rest Electrochemical Characterization of a Prepared Lanthanum gave crystalline materials . At higher silica to alumina ratios Impregnated Zeolite Modified Carbon Paste Electrode (La ( greater than 20 ) ( d ) and ( e ) another phase , which was 5 ZMCPE ) confirmed to be analcime was observed along with the Cyclic voltammetry was employed for the investigation of mordenite crystal. The formation of analcime along with the electrochemical properties of the zeolite modified carbon mordenite at higher silica to alumina ratios has been paste electrode (ZMCPE ) synthesized as previously reported by Hincapie, et al. [Hincapie , B. O., et al. , Synthesis described where 10 mM potassium ferrocyanide (K4Fe (CN ) of mordenite nanocrystals . Microporous and Mesoporous 10 6 ) and 0.1 M KClwere used as the electroactive specie and Materials, 2004. 67 ( 1 ) : p . 19-26 . — incorporated herein by the supporting electrolyte , respectively . The La- impregnated reference in its entirety ]. It was also observed that the area zeolite (La -MOR - 15, La -ZMCPE ) and the unmodified zeo of the XRD peaks for the prepared mordenite samples was lite (MOR -15 , ZMCPE ) were mixed separately with carbon higher than that of standard mordenite reported in the 15 graphite and paraffin oil in the ratios shown in Table 4 to literature . This can be attributed to the high crystallinity of obtain five composite electrodes ( A , B , C , D , and E ). The the prepared samples as can be confirmed from the size of resulting homogeneous paste was packed into the tip of a the crystals obtained . micropipette and cyclic voltammetry was carried out in Several morphologies of this crystal have been synthe potassium ferrocyanide . The cyclic voltammograms show sized in the literature , which includes; spherical, circular pie , 20 that composite electrode ( B ) with the ratio 65 : 5 : 30 (graphite : flat prism , ellipsoidal, hexagonal star - like prism and the like zeolite :paraffin ) has the highest anodic peak current as show [Mao , Y., et al. , Morphology - controlled synthesis of large in FIG . 17. FIG . 18 is a plot of peak current versus the mordenite crystals . New Journal of Chemistry , 2014. 38 ( 7 ) : La- MOR percentage . p . 3295-3301. — incorporated herein by reference in its entirety ] . Scanning electron microscopy (SEM ) micrographs 25 TABLE 4 of the prepared mordenite crystals are shown in FIG . 11 , FIG . 12 , FIG . 13 , and FIG . 14. The SEM results reveal that Composite ratio of prepared zeolite modified carbon paste electrodes a flat prism crystal was formed in the current work . The Graphite Zeolite Paraffin formation of the analcime growing phase at higher silica to Designation ( wt % ) (wt % ) ( wt % ) 30 alumina ratios was also confirmed by the SEM results . The A 70 0 30 relatively most pure form of mordenite was achieved with a B 65 5 30 ? 60 10 30 silica to alumina ratio of 15 and it was adopted for the D 55 15 30 purpose of further study . It will subsequently be referred to E 50 20 30 as MOR - 15 . Following characterization of the MOR -15 mordenite 35 zeolite , it was impregnated with 2 wt % lanthanum (La ) and The obtained results demonstrated reproducible anodic energy dispersive X - ray (EDX ) spectroscopy was per and cathodic peaks ascribed to Fe( CN ) 63- /Fe ( CN ) 6 +- redox formed . The EDX results ( Table 3 and FIG . 15 ) show that an couples at the surface of the zeolite modified carbon paste average of 1.68 wt/ o of the metal exists on the surface of the electrode . This was confirmed to be a quasi- reversible zeolite . The incorporation of La into the framework of the 40 system that showed a peak separation potential (AEp = Epa zeolite was also supported by 21 Al magic angle spinning Ep . ) equal to 163 mV (0.294-0.131 ) which is greater than nuclear magnetic resonance (MAS NMR , FIG . 16 ) , which the 59 mV often seen for reversible systems [Hassaninejad shows two distinct peaks at approximately 50 ppm and O Darzi, S. and M.Rahimnejad , Electrocatalytic oxidation of ppm . The peak near 50 ppm could be assigned to the 45 methanol by ZSM - 5 nanozeolite -modified carbon paste elec tetrahedral coordinated framework of Al atoms, while the trode in alkaline medium . Journal of the Iranian Chemical peak at around 0 ppm is due to the octahedral coordinated Society , 2014. 11( 4 ) : p . 1047-1056.— incorporated herein by extra framework [ Barras, J., J. Klinowski, and D. W. reference in its entirety ]. McComb, 27Al and 29Si solid - state NMR studies of dealu In order to determine the electroactive surface area of the minated mordenite. Journal of the Chemical Society, Fara- 50 composite electrodes ,the scan rate was varied from 5 to 400 day Transactions, 1994. 90 (24 ) : p . 3719-3723 . — incorpo mVs- for both the bare carbon paste ( composite A ) and the rated herein by reference in its entirety ]. FIG . 15 shows that La -MOR - 15 electrodes . FIG . 19 shows the effect of scan rate the intensity of the peak corresponding to the tetrahedral on peak current for composite B. An approximately linear coordinated Al atoms ( 50 ppm ) decreases after La impreg relationship was found between the anodic peak current and nation ( b ) . This implies that some of the Al atomshave been 55 the square root of the scan rate (R2 = 0.9992 ) for composite replaced by La in the framework of the zeolite . This lan B. FIG . 20 shows a plot of peak current versus the square thanum metal impregnated zeolite will henceforth be root of the scan rate for composite B. FIG . 21 shows the denoted as La -MOR - 15 . effect of scan rate on peak current for composite A. In contrast, a less linear relationship is obtained between the TABLE 3 60 anodic peak current and the square root of scan rate (R2 = 0.9881) . FIG . 22 shows a plot of peak current versus the Energy dispersive X - ray (EDX ) results for La- MOR - 15 square root of the scan rate for composite A. It can be Oxygen Aluminum Silicon Lanthanum Total concluded from such a relationship that ion accessibility to Spectrum ( wt % ) (wt % ) ( wt % ) (wt % ) (wt % ) electrode surface is enhanced by rare earth metal, such as Mean 56.48 4.39 37.45 1.68 100 65 lanthanum , impregnation . The electroactive surface area of the composite electrodes was estimated from the slope of plots of peak current versus US 10,495,601 B2 43 44 the square root of scan rate using the Randles - Sevcik sensor based on a built- in bismuth precursor . Analyst, 2005 . equation as given by formula ( II ) 130 (6 ): p . 971-976 . — incorporated herein by reference in its entirety ]. However , a longer accumulation time can alter the ip = ( 2.69x10 )n3 / 2 AD1/ 2,1 / 2C (II ) : electrode's surface thereby affecting its performance . As a In this equation , n is the number of electrons , v is the scan 5 result, an accumulation time of 120 seconds was adopted for rate , D is the diffusion coefficient ( cm² s - l) of the electro the purposes of the current procedure . In summary , the active species, A is the area of the working electrode , and C following conditions were employed for the subsequent is the electrolyte concentration in mol L - 1 . The electroactive construction of a calibration curve for Cd ( II ) detection using surface area estimated for the composite electrodes are 21.4 mm² and 25.9 mm2 for composites A and B , respectively . It 10 the zeolite modified carbon paste electrode of composite B can be concluded that modifying the carbon paste electrode ( i.e. 2 % -La- MOR - 15 composite electrode with a graphite : with a lanthanum impregnated zeolite ( i.e. La -MOR -15 ) zeolite :paraffin ratio of 65 : 5 : 30 ) prepared in the current leads to an increase in the electroactive surface area of the disclosure ; amplitude: 0.2 V , frequency : 40 Hz, accumula electrode . tion potential : -1.2 V , accumulation time: 120 seconds, 15 potential increment : 0.005 V. Example 5 After the evaluation of the different parameters , the strip ping of Cd (II ) over two different concentration ranges of Voltammetric Determination of Cd (II ) at a Prepared Lan 50-500 ppb (FIG . 27 ) and 5-50 ppb ( FIG . 28 ) were inves thanum Impregnated Zeolite Modified Carbon Paste Elec tigated . FIG . 29 shows the obtained calibration plot of Cd ( II ) trode (La - ZMCPE ) 20 over the concentration range of 50-500 ppb . FIG . 30 shows The electrode of composite B as previously described ( i.e. the obtained calibration plot of Cd ( II ) over the concentration La -MOR - 15 composite electrode with a graphite zeolite : range of 5-50 ppb . The stripping current was found to be paraffin ratio of 65 : 5 :30 ) was applied to the determination of linear with various concentrations of Cd ( II ) at both higher Cd ( II ) ions in 0.1 M phosphate buffer (pH = 4 ) using square and lower concentration ranges with correlation coefficients wave anodic stripping voltammetry with constant stirring at 25 of 0.999 and 0.998 for the higher and lower concentration 600 rpm during the accumulation of the analyte . Accumu ranges, respectively . The limit of quantitation was found to lation parameters such as accumulation potential and accu be 5 ug / L and the limit of detection (S /N = 3 ) was 0.12 ug / L . mulation time were evaluated before carrying out the Cd It can be concluded from the results of the analytical determination . performance parameters that the lanthanum impregnated Accumulation potential and accumulation time are crucial 30 zeolite ( i.e. La -MOR - 15 ) modified carbon paste electrode parameters when carrying out an anodic stripping voltam constructed in the current disclosure has a wide determina metric determination of metal ions such as the Cd ( II ) ion . tion range with a low detection limit. This is because unless an appropriate potential is applied The performance parameters of the current lanthanum enable the reduction and pre - concentration of the metal ions impregnated zeolite ( i.e. La -MOR - 15 ) modified carbon onto the surface of the working electrode prior to stripping, 35 paste electrode compare favorably with other electrodes for the sensitivity of the electrode is greatly affected . The effect the detection of Cd ( II) that have been reported previously of accumulation potential was studied by Kokkinos , et al. ( Table 5 ) [Rico , M. A. G., M. Olivares -Marin , and E. P. Gil , [ Kokkinos , C., et al ., Lithographically fabricated disposable Modification of carbon screenprinted electrodes by adsorp bismuth - film electrodes for the trace determination of Pb ( II) tion of chemically synthesized Bi nanoparticles for the and Cd ( II) by anodic stripping voltammetry . Electrochimica 40 voltammetric stripping detection of Zn ( II) , Cd ( II ) and Acta , 2008. 53 ( 16 ): p . 5294-5299 . — incorporated herein by Pb ( II ). Talanta , 2009. 80 (2 ) : p . 631-635 ; and El Tall, O., et reference in its entirety ]. This study demonstrated that al. , Anodic Stripping Voltammetry of Heavy Metals at choosing a high potential ( in the negative direction ) leads to Nanocrystalline Boron - Doped Diamond Electrode . Electro background hydrogen evolution . In addition , an accumula analysis , 2007. 19 ( 11) : p . 1152-1159 ; and Švancara , I., et al. , tion potential which is too low is insufficient to reduce the 45 Recent Advances in Anodic Stripping Voltammetry with metal onto the surface of the electrode before being stripped . Bismuth -Modified Carbon Paste Electrodes. Electroanaly For the current procedure , evaluation was carried out in a sis , 2006. 18 ( 2 ) : p . 177-185 ; and Siriangkhawut, W., et al ., 500 ppb Cd ( II ) solution in 0.1 M phosphate buffer (pH = 4 ) Sequential injection monosegmented flow voltammetric and the accumulation potential was varied from -1.4 V to determination of cadmium and lead using a bismuth film -0.6 V. FIG . 23 presents the resulting square wave voltam- 50 working electrode. Talanta , 2009. 79 (4 ): p . 1118-1124 ; and mograms. FIG . 24 presents the plot of current versus accu Kefala , G. and A. Economou , Polymer -coated bismuth film mulation potential and it can be seen that the maximum peak electrodes for the determination of trace metals by sequen current is obtained at -1.0 V. However, when this value was tial- injection analysis / anodic stripping voltammetry. Ana adopted for subsequent detection along with other param lytica Chimica Acta , 2006. 576 ( 2 ) : p . 283-289 ; and Lee , eters such as amplitude ( 0.2 V ) and frequency ( 40 Hz ), a 55 G.-J., H.-M. Lee , and C.-K. Rhee, Bismuth nano -powder very broad peak was obtained . Hence, a balance was nec electrode for trace analysis of heavy metals using anodic essary between obtaining a maximum peak current and a stripping voltammetry. Electrochemistry Communications, less broad peak . As such , an accumulation potential of -1.2 2007. 9 (10 ): p . 2514-2518.— each incorporated herein by V was adopted for the purposes of the current procedure. reference in its entirety ) . The current electrode compares In a similar manner , the accumulation time was varied 60 well and in fact has one of the lowest detection limits for from 20 seconds to 200 seconds . FIG . 25 shows the results . Cd ( II ) detection . The reproducibility of the stripping analy FIG . 26 is a plot of current versus accumulation time. sis of 50 ppb Cd ( II ) at the lanthanum impregnated zeolite Accumulation time is the time during which the analyte is ( i.e. La -MOR - 15 ) modified carbon paste electrode was also reduced at the working electrode (WE ) . It is generally examined by carrying out five consecutive measurements believed that lower detection limits can be obtained with a 65 with a single electrode . The relative standard deviation longer accumulation time [ Castaneda, M. T. , et al. , Sensitive (RSD ) was found as 2.7 % implying that electrode is stable stripping voltammetry of heavy metals by using a composite with reproducible Cd (II ) detection ability (FIG . 31 ).