South Dakota State University Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange
Electronic Theses and Dissertations
1979
Enhancement of Flameless Atomic Absorption Determination of Tellurium in Botanical Materials by Means of Solvent Extraction
Jeffrey D. Jung
Follow this and additional works at: https://openprairie.sdstate.edu/etd
Recommended Citation Jung, Jeffrey D., "Enhancement of Flameless Atomic Absorption Determination of Tellurium in Botanical Materials by Means of Solvent Extraction" (1979). Electronic Theses and Dissertations. 5047. https://openprairie.sdstate.edu/etd/5047
This Thesis - Open Access is brought to you for free and open access by Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange. It has been accepted for inclusion in Electronic Theses and Dissertations by an authorized administrator of Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange. For more information, please contact [email protected]. ENHANCEMENT OF FLAMELESS ATOMIC ABSORPTION DETERMINATION OF
TELLURIUM IN BOTANICAL MATERIALS BY MEANS OF SOLVENT EXTRACTION
BY
JEFFREY D. JUNG
A thesis submitted in partial fulfillment of the requirement s for the degree Master of Science, Major in Chemistry South Dakota State University .1979
SOUTH DAKOTA STATE UNIVE SITY L . APY ENHANCEMENT OF FLAMELESS ATOMIC ABSORPT ION DETERMINATION OF
TELLURIUM IN BOTANICAL MATERIALS BY MEANS OF SOLVENT EXTRACTION
This thesis is approved as a creditable and independent investi- gation by a candidate for the degree , Master of Science, and is accept- able for meeting the thesis requirements for this degree . Acceptance of the thesis does riot imply that the conclusions reached by the can-
" didate are necessarily the conclusions of the ·maj or department .
David C. Hilderbrand Date Thesis Advisor
Harry G. Hecht Date Head , Chemistry Department ABSTRACT
The use of sodium diethyldithiocarbamate and ammonium iodide as
complexing agents for the extraction of tellurium from botanical materials is investigated . Flameless atomic absorption spectrophoto metry is used as the method of analysis . The acids used to wet ash the samples are examined for.their contribution to interferences in the extraction and analysis processes . The extraction parameters needed for complete extraction of the tellurium are described . The instrument parameters required for the mos t precise and accura�;e analys�s of tellurium are described .
The two extraction processes are compared to determine which method is more suitable for the extraction of tellurium from botanical materials . ACKNOWLEDGEMENTS
I would like to express,my deepest gratitude to the following people:
To Dr . David Hilderbrand for his friendship� ·encouragement , and guidance throughout the course·of'my studies . I would like to thank him for allowing me to do things in my own way .
To Carol Haugen ,. Pam Krage , and Debbie Pravacek for their friendship . They made my studies at SDSU a thoroughly enjoyable experience .
To Carol for typing this manuscript .
I would espec ially like to express my gratitude to Dad for his guidance throughout the years . TABLE OF CONTENTS
PAGE
STATEMENT OF PROBLEM .. 1
LITERATURE REVIEW 2
EXPERIMENTAL
Samples...... • • • . 18
Reagents . . . • ...... 18 Methods Us ed to Clean Glassware. 20
Ashing of Samples ...... 20 Instrument Parameters ...... 22 Treatment of Standards and Blanks ... 24 Extraction of �ellurium with the NaDDTC System . 25 Extraction of Tellurium with the Iodide System 26
RESULTS AND DISCUSSION
Ashing of Samples ...... 32 Effect of In strumental Parameters . . . 33 .
Analysis of Standards and Blanks ...... ••.. 38 Extract ion of Tellurium with the NaDDTC System . 47 Extract ion of Tellurium with the Iodide System . 60 Comparison and Summary of Methods. 63
Chemical States of Tellurium . . . . . 65
CONCLUSION .• 68
LITERATURE CITED. 69 LIST OF FIGURES
FIGURE PAGE
1. EFFECT OF CHARRING TEMPERATURE ON SENSITIVITY. . 35
2. EFFECT OF ATOMIZING TEMPERATURE ON SENS ITIVITY . . 36
3. EFFECT.OF ARGON GAS FLOW ON CALIBRATION CURVES . . 37
4. EFFECT OF ACID CONCENTRATION ON SENSITIVITY . . . . 40
5. COMPARISON OF CALIBRATION CURVES FOR ETHANOLIC Al:m AQUEOUS STANDARDS...... 41
6. CALIBRATION CURVE FOR CONSTANT VOLUME WITH VARYING
CONCENTRA'I'ION. . . . . ·• . . . . . • ...... 43
7. CALIBRATION CURVE FOR CONSTANT CONCENTRATION WITH VARYING VOLUME ...... 44
8. CALIBRATION CURVES FOR STANDARDS OF DIFFERENT
CONCENTRATIONS IN AN AQUEOUS SOLVENT . . •· . . .. . 45
9. CALIBRATION CURVES FOR STANDARDS OF DIFFERENT CONCENTRATIONS IN AN AQUEOUS SOLUTION CONTAINING 20 PPM NICKEL ...... 46
10. EFFECT OF CUPFERRON CONCENTRAT ION ON THE AMOUNT OF TELLURIUM EXTRACTED ...... 49
11. EFFECT OF BUFFER CONCENTRATION ON THE AMOUNT OF TELLURIUM EXTRACTED ...... 53
12. EFFECT OF THE SOLUTION CONCENTRAT ION ON TELLURIUM LOST DURING EVAPORATION OF ORGANIC EXTRACTS ...... 56 LIST OF TABLES
TABLE PAGE
1. EFFECT OF ACID CONCENTRATION ON THE AMOUNT OF
TELLURIUM EXTRACTED .· ...... • . . • • • • 51
2. EFFECT OF SAMPLE MASS ON THE AMOUNT OF TELLURIUM
. . � . . EXTRACTED ...... • ...... 62 STATEMENT OF PROBLEM
In recent years there has been a growing interest in the physio logical and toxicological significance of tellurium in zoological an d botanical systems . The importance of tellurium in these systems is unknown due to an absence of an analytical method which is capable of detecting tellurium at the concentrations which are inherently present in living organisms . Interest in tellurium has been stimulated by its relationship to selenium in the periodic table , an element that is well known for its essen�ial and toxic· effects (1).
The purpose of this research was to investigat e the use of a combinat ion of solvent extract ion and flameless atomi c absorption spectrophotometry as a means· for the determination of tellurium in biological systems . Flameless atomic absorption provides a great er sensit ivity than most report ed methods .
Solvent extraction potentially yields two advantageous effects .
First , extraction of the metalloid may result in a simpler matrix which reduces int erference effects in the analysis step . Second , the extraction process may result in chemical enrichment , making analysis more accurate for species of low concentrat ions . This extract ion enrichment step is important in view of the low tellurium levels in botanical samples compared to the detection limits of flameless at omic absorption . It also is important in eliminat ing potential matrix interference effects. LITERATURE REVIEW
Tellurium is a silver white metalloid which is very reactive, forming a dioxide at room temperature (2). It ha s a boiling point of
1390°C and is soluble in a mixture of .nitric and hydrochloric acids, forming tellurous (H2Te03) and telluric (Te(OH)5) acids. Tellurous acid readily dehydrates to form the dioxide. Telluric acid decomposes at 300°c to form the trioxide which in t�rn will decompose at 43ooc to form the dioxide. Tellurium dioxide is arnphoteric, being soluble in hydrochloric acid and in alkali hydroxides solutions. It has a boil ing point of 1245oc and will be reduced by carbon at red heat.
Tellurium has a formal oxidation state of -2 in its hydrides and their derivatives. It also forms compounds :in which it has a formal oxidation state of +1, +2, +4, or +6. Nearly· all of the tellurium compounds are covalent in character, as in the other groups of metalloid elements. Thus the halides are generally low melting, volatile, and easily hydrolyzed solids. Tellurium tetraiodide will form in stochiometric amounts of HI. The extraction of TeI4 into nonpolar solvents has been reported (3). Hydriodic acid will dissolve
TeI4. All tellurium tetrahalides will form anionic complex species
2 of the type Tex6 - in an excess of the aqueous halogen acids. The order of stability of the complexes formed is r- >Br- > ci- > r-.
2 The anion Ter6 - will also be formed in a mixture of KI and strong acid. This iodide complex is yellow in color and is frequently used in the photometric determination of tellurium.
Tellurium will combine with several reagents forming complexes 3
which can be extracted ·forming solutions whose molar absorbtivity can be measured (4). These reagents include complexing agents such as dithiocarbarnic acid and its derivat ives, Bismuthiol II, diantipyryl methane and its derivatives , pyrazonlone , and butylrhodamine B.
The uses of tellurium are primarily as an additive to alloys of steel , copper , and lead to increase their resistance to corrosion; as a vulcanizing agent for natural rubber; as a rap id diagnostic test for diptheria , and as a thermocoupling material in refrigerat ion equipment ( 5).
Tellurium has not been shown to play essential roles in the trace element biochemistry of living organisms (6). It is , however , a potent biotoxin . Information on the toxicology of tellurium is limited , but it is believed to resemble arsenic more than selenium in its toxic action . Tellurium binds uniformly to soluble proteins in the blood, has been implicated in nerve and brain damage in rats , and is readily transported across the placenta barrier . Reduction in general activity and in longevity has been demonstrated in mice fed sub-toxic doses ( 2 ppm) of tellurium in water , but no influence on _ carcinogenicity or on the production of other tumor types has been observed.
No other data has been reported regarding the effects on marrunals of long-term low-level exposures of tellurium . A primary cause for the absence of this information is a lack of an analytical method which will determine the concentrations of tellurium which are inherently present in living organisms . Even for the more sensitive 4
methods of analysis , a · preconcentration step is usua lly needed prior
to the actual determination . Solvent extraction is one such process used for con centrating the metalloid .
A unique feature of solvent extr�ction , particularly for metal and metalloid ions , is the large variation in distribution rat ios and separation factors made possible by controlling the chemical parameters of the system (7). Although most simple metal salts are highly soluble in aqueous media and relatively insoluble in organic solvents , it is possible to employ a variety of chemical approaches to incorporate the metal in an organic species . Characteristics such as hydrogen bonding , donor-acceptor , or dipole-dipole interaction can be changed , thereby varying the extract ion efficiency . Variation in pH provides another chemical means of changing the characteristics of organic compounds , thereby improving the extract ion selectivity . Thus , solvent extraction lends itself well to the removal of tellurium from a dilute solution while simultaneously increas ing the concentration.
In various methods of analysis of trace metals , organic solvents may interfere . The metals can be placed into an aqueous media by
' several means . The organic extracts can be digested with acids or hydrogen peroxide or they can be evaporated and the residue dissolved in an aqueous solvent . Makarov and Mishust ina extracted Se and V as dithiocarbamates into CC14 (8}. They then re-extracted the metal from the organic phase with a 10% solut ion of another metal ion . This investigation indicated a series of ions which can displace all ions following them in the series . This series of metal ions is: Hg2+ , 5
+ 2+ 2+ 3+ 2+ 3+ 2+ 3+ 4+ 4+ 5+ Ag , Cu , Ni , Bi , Cd , Sb , zn , Fe , Te , Se , v , and
2+ Mn .
The principle methods of. analysis for tellurium are photomet�y and atomic absorption spectrophotometry. To a lesser extent, methods such as neutron activation, and fluorimeter are also used.
Photometry is a common method of analysis for tellurium because many reagents used to extract the metalloid will also develop complexes which have la.I?ge molar a�sorptivities. Cheng reacted tellurium (IV) with Bismuthiol II to form a colored complex and then extracted the complex with chloroform (9). The sensitivity and precision of the method.were found to be 5 ppb and± 2%, respectively. Interference studies were completed by extracting tellurium from standard solutions containing foreign ions. The ions of Fe, Cu,. Au(III}, Pt(IV), V(V),
Se, and No2- interfered with the extraction.
Bode used diethyldithiocarbamate to extract tellurium (10.}. Prior to extracting the tellurium, interfering metals were removed from the solution with cupferron. Potassium cyanide and EDTA were used as masking agents. A buffer was added, the pH was adjusted to 8 . 5 - 8. 8, and sodium diethyldithiocarbamate was added. At a lower pH the iritensity of the absorbing chelate will fade rapidly. The colored complex was extracted into carbon tetrachloride. The sensitivity of the method was 247 ppb for 1% A.
Luke coprecipitated tellurium in lead or copper along with arsenic. (11) The precipitate was redissolved and sodium diethyl- dithiocarbama te was added. The colored complex was then extracted 6
into chloroform and the absorbance of the solution was measured .. The sensitivity of the method was 90 ppb for 1% A.
Janus Green {3- (diethyla.mino )-7- ( ( P- (dimethylamino ).-phenyl) azo) -s phenylnhenazinium chloride} has been used as a reagent for the extraction and photometric determination of tellurium (12). After the reagent was added to a solu�ion containing tellurium, the complex was extracted into a mixture of benzene and dimethyl ketone . The absorbance of the organic_ extracts was measured against a blank. The sensitivity of the method was 53 ppb for 1% A.
Tellurium has been extracted from technical grade selenium by the use of diantipyrylmethane (DAPM ) (13). The chloride complex of tellurium (IV) with DAPM was quantitatively extracted with dichloroethane from hydrochloric acid solut ions . Selenium (�V) remained behind in the aqueous phase at all acid concentrations . In the determination of the tellurium, the chloride complex was converted to the bromide complex with DAPM and the absorbance of the resulting solution was measured. A similar method of analysis was used for the determination of tellurium in lead, bismuth, and copper .
Tellurium in urine was determined by Hanson (14) . After digest ing
200 ml samples of urine with nitric and perchloric acid, the solut ion was cooled and the pH was adjusted to 7 with 1:1 NH40H, The white precipitate which formed was dissolved with· dilute HCl and 6 ml of concentrated HCl was added to make the solution 1 N in hydrogen ion .
Sodium iodide was added to obtain an iodide ion concentration of 0.6 N.
The tellurium iodide complex was then extract ed into a mixture of ether 7
. and n-amyl alcohol . The organic extract s were washed with 1 N HI.
The extract s were then evaporated and oxidized with hydrogen peroxide thereby placing the colored complex into an aqueous solution . The absorbance of this solution was measured. The sensit ivity obtained was
630 ppb for 1% A and the precision was found to be ± 7.9%. Mercury , gold, palladium , platinum , rhodium, and iridium interfered.
In recent years at omic absorption spectrophotometry has become an important method of analY-sis for tellurium . It is more sensitive than photometry an d is generally less susceptible to int erferences caused by o�her metals . Although at omic absorption spectrophotometry was introduced in the mid 1950's , it did not become a commonly used tool for analysis until the mid sixties . At first the methods involved the us e of flame systems , however, other more sensit ive techniques have since been developed which are well suited for tellurium analysis .
These techniques involve the us e of flameless methods for atomizing the element of interest . Generally , an electrically heated graphite cell is used. Due to their ease of applicat ion, flame systems are still frequently used when the sensitivities of the other systems are not needed.
The theory behind both flame and flameless atomic absorption spectrophotometry is essent ially the same (i5). Radiat ion from an external light source is passed through a sample cell . The light source is normally a hollow cathode lamp or an electrodeless discharge lamp . The radiat ion emits the spectral lines that correspond to the energy required for an electronic transition from the ground state 8
to an excited state.
In the cell there are free, unexcited atoms capable of absorbing radiation from the externa l source when the radiation corresponds· exactly to the energy required for a transition of the test element from the ground to the excited level. Unabsorbed radiation then passes through a monochromator that. isolates the exciting spectral line emitted by the light source. The absorption of radiation from the light source depends on the population of the ground state, which is introduced into the cell. Absorption is measured by the difference in t�ansmitted signal in the presence and absence of the test element.
In flame systems the sample cell is a flame. When the sample solution is introduced into the flame several events occur in rapid succession. First, the water or other solvent is evaporated, leaving minute particles of dry salt. Second, the dry salt is vaporized, or converted into the gaseous state. Third, a part or all df the gaseous molecules are dissociated to neutral atoms or radicals. These free neutral atoms may then absorb light from the external source and be excited.
Generally in both flame and flameless systems the samples need to be in the form of a solution. If the sample is a solid, it is either wet or dry ashed and then dissolved in a suitable solvent.
Depending on the type and size of the sample, the sample matrix may cause interference during the analysis. The interference caused by the matrix is usually due to physical interferences. In flame systems, particulate matter in the flame is responsible for light 9
scattering . This may arise from unevaporated droplet s, but more likely
from unevaporated or refractory salts left following desolvation .
Sample solutions which are very high in total solids result in a·
reduction in signal . Large s·alt part.icles from concentrated solutions
tend to hinder solvent evaporation. Another cause of interference is
molecular absorption , owing to the format ion of molecular species in
the flame that are not dissbciated . Interf�rences will occur if these
molecular species absorb-at the same wavelength as the analyte .
An instrumentation accessary may be used to compensate for back-
ground absorption (16). This device employs a hydrogen or deuterium
lamp which emits continuum radiation . The continuum beam is ins erted
into the optical path by a chopper which provides a rapid alternation
. of the deuterium and exciting ·beams at a frequency to which the
amplifier is tuned. Both beams pass through the vapor in the cell and reach the detector . The deuterium signal can be subtracted electron-
ically from the exciting beam signal which contains the sum of back-
ground and atomic absorption signals .
Solvent extraction can be used to remove most interferences from
a system . By carefully choosing the extraction conditions , the metal
of interest can selectively be removed from its original solution and
into another which is relatively free of interfering species. The
·removal of this interference is of particular importance in the
determination of tellurium since a broad band background absorbance
due to matrix materials occurs at the tellurium wavelength (17).
Flame atomic absorption spectrophotometry has been used to 10
· determine tellurium in several types of samples . Chakrabarti determined tellurium at the parts per million level in aqueous samples from metallurgical processes (18)� He found that tellurium cannot be accurately determined in solut ions containing copper ions , nitrate ions and free nitric acid using a calibration curve constructed using aqueous standards . Tellurium was determined in the parts per billion range by two different First , the tellurium was coprecipitated . methods . with arsenic, the precipitate was redissolved, and the tellurium was determined on spectrophotometer. The second method involved extract ing potassium hexaiodotellurate (K2TeI6) or tellurium diethyldithiocarbamate
(Te(DDTC } 4) with methyl isobutyl ketone (MIBK) . The organic extract was then aspirated into the flame and the tellurium was determined.
The sensitivit ies were 1 2 0 ppb for the K2Tel6 complex in MIBK and 90 ppb for the Te(DDTC )4 complex in MIBK . These sensit ivities are reported here as the concentrat ion required to give 1% absorption.
The sampling boat technique was used by Beaty (19 ). . In some types of samples , the tellurium was extracted from 4 M HCl solutions into methyl isobutyl ketone. The organic extract was placed into the sampling boat , dr ied with a heat lamp , and the boat was placed in the flame for.the determination . In samples where matrix constituents caused chemical interference with the extraction , a preliminary separation was employed by coprecipitat ion of the tellurium with selenium . The sensitivity obtained by this method was 5 ppb . The same method was applied using a_ Delves cup and a sensitivity of 0.5 ppb was obtained. 11
Tellurium was determined in steel by Marcec , Kinson , and Belcher
(20). The steel sample was dissolved an d sodium diethylt hiocarbamate was added to the solut ion . The tellurium complex was then extracted
into amyl acetat e and the organic extracts were aspirated into the flame for the determination . A sensit ivity of 300 ppb was obtained.
Tin (II) interfered seriously with the extraction . Although other . metals were extracted along with the tellurium , _ they did not cause any interference in the actual analysis .
Chao , Sanzolone , and Hubert used both £lame and flameless at omic absorption to determine tellurium in geological materials ( 2 1) . The sample was dissolved in hydrobromic acid and bromine . The bromide was extracted into methyl isobutyl ketone a�d this organic extract was either aspirated into the flame or placed into the graphite tube for the determination . Sensitivities for the method were 80 ppb for the flame analysis and 3.3 ppb for the flameless analysis . Assuming a max imum sample volume of 100 ul , 3.3 ppb Te in the sample solut ion corresponds to 0. 33 ng Te for 1% A. Iron caused suppression of the absorbance read ing in both types of determinations , however reducing the iron (III) with ascorbic acid eliminated this interference . In the flame analysis , interference was also caused by light scattering and molecular absorption .
Fiorino developed a sequential determination of tellurium in food and biological samples via rapid hydride evolut ion and at omic absorption spectrophotometry ( 22). The sample was digested, dissolved , and NaBH4 was added as a reductant . The hydrides which were formed were swept 12
into the flame . The sensitivity of the method was found to be 11 ppb
Te . The only interference was caused by organic moiet ies wh ich were
not completely oxidized during the digest ion step .
Cheng an d Agnew det ermin�� tellurium in biological mat�rials (17) .
The sample was digested , dissolved, and placed in a microsampling boat .
The boat was placed in the flame and the analysis was completed .
Watterson developed a m�thod for the analysis of tellurium in
rocks (23) . The sample was digested and dr ied . The tellurium was
extract ed from the residue with HBr and then coprecip itated with
arsenic by using H3P02 as a reducing agent . The precipitate was
dissolved in a HBr-Br solut ion from which the tellurium was extracted
into methyl isobutyl ketone . This organic extract was then aspirated
into the flame .
In flameless systems the sample cell is usually a graphite tube
or cup which is heated by electrical resistance (�5}. The light path
from the external source passes through the center of the tube . The
cell is purged with an inert gas such as nitrogen or argon . The
flow of this gas can be interrupted during the atomizing step causing
an increase in the sensit ivity. The cell is heated in three stages .
First, the solvent is evaporated , then the temperature is raised to
ash the sample; and finally the unit is raised to incandescense to atomize the sample .
The benefits of flameless cells are high sens it ivity , the
capability of handling small samples , direct analysis without pre
treatment (particularly for biological fluids) , an d low noise signal. 13
However, matrix interference effects are often greater than in flame systems and the precision, typically 5-10%, compares unfavorably with
that of flame, typically 1% • .
In flame systems molecular species are dissociated by the flame forming ground state atoms ( 16 ) . However, in flameless systems the atomic vapor may be formed . by other mechanisms. Campbell and Ottaway presented a mechanism for the production of atoms in which the carbon
�f the graphite furnace �ntered into the reaction (24). The reaction which they proposed is:
It has been proposed (2 5) that in actuality, atom formation is a combination of the above mechanism and of the dissociation of molecular species. The carbon of the graphite tube may also react with metals forming metal carbides (26). This may decrease the sensitivity of the analysis if the carbide is thermally stable.
Several studies have been completed to determine the effect of matrix interferences in the furnace and the suitability of solvent
extraction to remove these interferences.
Since interferences due to the sample matrix are greater in flameless systems, it is even more necessary to remove these
.interferences with a process such as solvent extraction. Smeyers
Verbeke, Michotte, Van den Winkel, and Massart studied the effects of chlorides, nitrates, phosphates, and nitrates of Na, K, Ca, Mg, Zn, and La on the flameless determination of copper and manganese (27}.
SOUTH DAKOTA STATE UNIVERSITY LIBRARY 349782 14
Julshamm studied the inhibition of response by perchloric acid in flameless atomic absorption (28). Ten different metals were examined and it was found that perchloric acid decreased the response of all of the metals . Removing the perchloric acid by evaporation decreas ed the interference. This study was significant in that perchloric acid is used in the digestion of most biological samples .
This interference can be eliminated by use of solvent extraction .
Genera�ly in flameless analysis , pretreatment of the sample is not needed . However , in some combinations of matrix and analytes unusual analytical difficulties may occur . These difficulties may be due to relatively non-volatile matrix components or a very volatile analyte . In these cases it may not be possible to remove an inter-
. fering matrix during charring without also removing the analyte at the same time . Prior to the analysis , the addition of a reagent to these samples will cause a chemical change to occur during the drying or charring step . Matrix modification can decrease the volatility of the analyte to prevent its volatilization during the charring step . It can also increase the volatility of the matrix to promote its removal
prior to atomization . Ediger treated selenium , cadmium , mercuc ry, sodium chloride , and gallium with nickel , sulfate , sulfide , ammonium nitrate , and hydrogen peroxide , respectively (29). In each case the matrix modification increased either the sensitivity or the precision of the analysis .
Regan and Warren added ascorbic acid, tartaric acid , or sucrose to solutions of lead , copper or gallium to eliminate matrix interferences
(30). 1 5
Runnels , Merryfield, an d Fisher developed a method for improving
the detect ion limits for some elements with the graphite furnace
atomizer (26). The inner surface of the graphite tube was treat ed with
a carbide forming element such as lanthanum or zirconium. The carbide
coating prevented physical contact between the carbon of the furnace
and the samples . This precluded further carbide format ion by elements
of the sample . The thermal characteristics ·of .the furnace were not
altered by �he coating and an improvement in the detection limit was
demonstrated for berylliwn , chromium , manganese, an d aluminum .
Welcher , Kriege , and Marks determined trace quantities of
tellurium in high temperature alloys by · flameless atomic absorption
spectrophotometry (31). They found that some samples had poor
detect ion limits because of high background absorbance . By the use of
an automat ic deuterium background correction system , this interference
was essentially eliminated. The char cycle was necessary to minimize
background absorbance , even though no organic matter was present . The
reasons for this are , first , volatile matrix components are removed
during this cycle, thus reducing the background. Secondly , thermally
unstable fluorides and nitrates may be converted to oxides and carbides which result in lower background absorbance upon atomization. There was a rapid decrease in the sensitivity at relat ively low charring
temperatures . This was probably due to the high volat i ities of the
fluorides and oxyfluorides . Loss of tellurium at high charring
temperatures may be due to the format ion of more thermally stable
oxides or nickel bimetallic compounds. 16
A variety of methods of analysis other than photometry or atomic
absorption spectrophotometry have been applied to tellurium . Tellurium
was det ermined in geological materials in the parts per billion range
by Hubert (32). After digestion of the sample, the tellurium was
extracted into methyl isobutyl ketone and then into water. The
tellurium was then determined by the catalytic reduction of gold in
the presence of copper (II) chloride and hypoph�sphorus acid. The
resulting p�ecipitate was filt ered and its color was visually compared
to a standard precipitate . Th e sensitivity of the method was 2 ppb .
Hµbert also applied a similar method to the det ermination of tellurium
in vegetat ion (33).
Bovay and Marcantonatos developed a photoluminescence technique
for the determinat ion of tellurium in seleniu� (34). Orthotelluric acid and 2,4 ,4-trihydroxybenzphenone formed a fluorescent chelate with
excitation and em ission wavelengths at 426 and 465 nm , respectively .
The sensitivity was in the nanogram per milliliter range with a precision of± 9.5%. Chromium (VI), iron (III), and chloride
interfered.
A polarographic method was used to determine tellurium in
concentrations from 6 to 255 ppm . The supporting electrolyte consisted
of NH4c1 (0.75%), NH40H (0.25%), sodium ion (0.1%), and gelat in (0.002%} (35).
Gladney and Rook reported a method for the simultaneous determina
tion of tellurium and uranium by neutron activation analysis (6). The
procedure utilizes thermal neutron activation followed by sample 17
combustion and a gas phase separat ion of the volatile radionuclides of interest . The method was successively us ed to determine the tellur ium concentrations of 7 to 12,10� ppb in Standard Reference Materials.
In our investigat ion we examined two possible methods of extraction . The two methods were chosen because they appeared to be ideally suited for the extraction ·of tellurium from biological materials .
The extraction of tellurium as described by Bode (10) was used .
This method seemed adaptable to biological samples because selective extraction of tellurium could be obtained by adj ustment of the extraction conditions . This prevented the extraction of other metals which are present in greater concentrat ions than tellur ium in biological samples .
The second method we utilized was developed by Hanson to extract tellurium from urine (14) . This procedure was unaffected by high salt concentrations in urine , therefore it was reasoned that the salt concentrations in biological samples would not interfere with the extraction .
After the extraction , the tellurium was determined by the us e of flameless atomic absorption spectrophotometry because of the high sensit ivity of this method . EXPERIMENTAL
The instrumentation and .procedures used in the inves�igation are described in the following sect ion . Reagents which required special treatment or whose purity was of major significan ce are discussed.
Samples
The samples used in the· initial staJes of the investigat ion were corn samples.grown near Milbank , South Dakota. C9rn samples grown near Madison , South Dakota were used for the latter part of the investigation . These samples consisted of the entire corn plant except for the roots. The samples were collected in the late fall . A variety of other s�mples were also �sed. These samples included materials such as alfalfa , needles from different types of coniferous trees, and leaves from deciduous trees. Corn plants grown in tellurous and telluric rich cultures were also used as samples .
Standa�d Tellurium Solutions
Metallic tellurium , Johnson Matthey Chemicals Limited , spectrographic grade , was us ed to prepare the standard solut ions . A stock solution of 1000 ppm was prepared by dissolving 1.0000 grams of tellurium in 5.0 ml of nitric acid. The resulting precipitate was redissolved· with a minimum of hydrochloric ·acid and the solution was diluted to 1.00 i with deionized water . After setting for several months, white crystals precip itated out of the stock solution . There fore a _ 100 ppm stock solution was made by dissolving 0.1000 grams of
I . 19
tellurium and diluting it to 1. 00 i.
Sodium Diethyldithiocarbamate
Sodium diethyldithiocarb�mate (NaDDTC ), Matheson Coleman and
Bell , was used as provided .
Sodium Iodide
Sodium iodide , Fisher Scient ific Company , laboratory grade , was used as provided.
Ammonium Iodide
Amm onium iodide , Matheson Coleman and Bell, ACS reagent , was used as provided .
Hydrochloric Acid
Hydrochloric acid (HCl), Fisher Scientific , ACS reagent grade , was used as provided .
Nitric Acid
Nitric acid (HN03 ), Fisher Scientific, ACS reagent grade , was glass distilled.
Perchloric Acid
Perchloric acid (HCl04-70%), Fisher Scientific Company , ACS reagent grade used as provided .
Hydrogen Peroxide
Hydrogen peroxide (H202- 3%) , Baker Analyzed Reagent , was used as provided . 20
Buffer for NaDDTC Extraction
A buffer containing EDTA was prepared by dissolving 5 g of boric
1 1 100 acid, g of EDTA, and g of KH2Po4 in ml of H2o. The pH of. this
solution was then adjusted to .-8. 6 with 10% NaOH.
Methods Used to Clean Glassware
All glassware used in the investigation was washed with an Alconox
solution followed by rinses with distill�d water, 10% hydrochloric acid, and deionized water. The Kjeldahl flasks were subjected to
boiling 5% hydrochloric acid and then rinsed with deionized water.
All glassware which came in contact with organic materials was cleaned with chromic acid prior to the washing described above.
Ashing of Samples
All samples were ground with a Wiley Mill Model 2 prior to ashing.
Samples were ashed by wet oxidation using either a nitric and perchloric
acid mixture or a nitric, perchlor�c, and sulfuric acid mixture. In
the initial stages of the investigation, tellurium analysis was
performed on the solutions obtained from the d.igestion process. There
fore, a study was conducted to determine if th e acids used in the
digestion were contributing to interferences which occurred during the actual analysis. To determine if the amount of nitric acid affected
the readings, different amounts of acid were added in excess to that
needed for the actual digestion. The extra acid was then evaporated.
The effect of sulfuric acid was determined by analyzing samples which were digested with or without sulfuric acid. The effect of perchloric 21
acid on the analysis was determined by adding various amounts of perchloric acid to the samples before the digestion .
Ashing was performed on ·a Kjeldahl rack using either 30 ml or 100 ml Kjeldahl flasks . The Kjeldahl rack exhausts the fumes through a water aspirator, preventing the release of acid fumes to the hood vent and thus avo iding the buildup of explosive perchlorat es in the hood exhaust system . Approximately 0.5 ml of keros ene was added to each sample. This significant:ly decreased the amount of frothing which occurred during the initial stages of the digestion . Preliminary oxidat ion was performed with HN03 to remove all easily oxidizable material . When the evolved nitrogen oxides decreas ed, the samples were cooled and 5 ml of a 2:1:1 solution of HN03, �Cl04 , and H2S04 was added. The samples were then heat ed until perchloric acid fumes appeared with no charring of the samples occurring . If charring occurred, 5 ml of HN03 were added and the digest ion was continued .
The effect of rate of digest ion on interferences occurring during the analysis was examined by digesting similar samples using different temperature settings on the Kjeldahl rack . Interferences caused by the extent of the digestion or the amount of insoluble material remaining after th� digestion were examined. This was done by an alyzing the solution when the insoluble material was suspende� in the solution and when the material had settled to the bottom of the flask.
One gram samples were used for this study . It was also determined if tellurium was lost during the digestion by spiking some samples with tellurium before the digestion and spiking other samples after the 22
digestion.
Instrument Parameters
All flameless analysis was performed on a Perkin Elmer Model 503
2100 Atomic. Absorption Spectrophotometer with a Perkin Elmer HGA
Graphite Furnace and a deuterium arc background corrector. A Perkin
Elmer Model 5 6 Recorder was used. The recorder response time was
determined. The light ·source was a Westinghouse high intensity
tellurium hollow cathode lamp. The slit width was set at 0. 2 nm. 0 The line at 2141.7 A was used as .the analytical line. Throughc·1t
the investigation various readout modes were used in determining the
absorbance. These modes included absorbance, concentration, inte-
gration, and peak read modes:
Eppendorf pipets were used to introduce the samples into the
furnace. The effect on the precision of the analysis by reusing the
disposable tips was ascertained.
Furnace parameters of drying, charring, and atomizing times and
temperatures were optimized for several types of samples. These
sample types included aqueous standard solutions, digested samples, and carbon tetrachloride extracts. For the aqueous solutions the
drying, charring and atomizing temperatures were 13ooc, 5oo0c, and
2100°c, respectively. The drying cycle was set at 15 seconds p r
10 ul of solution. The sample was charred for 30 seconds and atomized for 7 seconds. The effect of completely eliminating the
charring step was ascertained. For the carbon·tetrachloride extracts
the �rying temperature was reduced to 90°C. 23
The efficiency of the deuterium background compensator was
determined when analyzing the CC14 extracts by measuring the ab
sorbance of a non-resonant line near the tellurium analytical line .
The amount of background absorbance present at the tellurium line was determined by analyzing extracts without the use of the
background compensator.
The graphite tube was coated with La, Mo, or Zr and the effect on the absorbance readings was determined . After coating the furnace with La and Zr, the peak heights were integrated for different time
periods to determine if the precision would be affected . The atomizing temperature was optimized after coating the tube .
The effect of interrupting the inert gas flow on the calibration curves was determined . This was done for aqueous standards and
standards which were made with a water-ethanol solvent .
Samples of high tellurium content were analyzed by a flame system . This was done to determine if low sensitivities obtained when
using a flameless system was due to incomplete extraction of the
tellurium or due to matrix effects in the furnace. The sample used
for this analysis was dissolved in a 1:1 EtOH-1% HC104 solvent . The analysis was completed on a Perkin Elmer Model 303 Atomic Absorption
Spectrophotometer using a premix burner with an air-acetylene flame .
A Perkin Elmer signal averaging unit was used as a readout. An average
value from four individual absorbance readings was determined for each sample . 24
Treatment of Standards and Blanks
The absorbances of acid blanks were determined . The effect of the use of boiling ch ips in the digestion on the absorbance was determined by digesting blanks using glass rings instead of boiling chips.
The difference in absorbance readings was determined for standards which contained no acid and standards. which were 1-4% acid.
The absorbances of standards prepared with a series of acids over the range of 1-4% was determined. The acids used were nitric, sulfuric, p�rchloric, and hydrochloric acids .
To det ermine their effect on the absorbance readings, salts of sulfate, chloride, or perchlorat e ions were added to standard solutions .
These anions were chosen because they are present in the acids used for digest ing or dissolving the samples.
Standards were run through the digestion and extraction processes to determine the amount of tellurium recovered . A standard with a higher concentrat ion was analyzed to determine if it would be affected by the same interferences which occurred with standards of low concentration . The effect of adding a nickel compound to standards was determined. The concentrat ion of the nickel was 20 ppm . The effect of removing the pyrolytic coating from the graphite tube on the analysis of standards was also determined.
Calibration curves were obtained for aqueous standards and for standards made with an ethanol-water solvent . The linearity of these curves were compared . 25
Equal volumes of standards of various concentrations were placed in the furnace , the absorbances were measured, and a calibrat ion curve was plotted. Another calibration curve was obtained by placing various volumes of a single standard in the furnace and measuring the absorbance .
For the calibration curves the absorbance was plotted against the total mass (ng } ·of telluriu:m placed into the furnace .. Acid was added to the standards so that their matrix would be similar to that of the samples.
Extraction of Tell urium with the NaDDTC System
Pre-extract ion with Cupferron . Tellurium was removed from the digested solution by the use of solvent ext�act ion . Several metals were pre-extracted from the solut ion with cup.ferron so they wouid not interfere with the extract ion of the tellurium .. This pre-extract ion was initiated by transferring the digested sample quantitatively to a
150 ml Pyrex beaker . The pH was adjusted to 1-2 with NaOH and the cupferron was added . The solution was transferred to a 125 ml separatory funnel and the cupferronates were then extracted with three successive 20 ml portions of chloroform . The effect on the analysis of using various amounts of cupferron in the pre-extract ion was determined. This was done by placing different quantities of the reagent in sample solut ions when they were pre-extracted .
It was ascertained if any tellurium was lost during the pre-extraction process by analyzing both the organic and the aqueous phases for tellurium . To determine the nece ssity of the pre-extraction 26
step, analytical results of pre-extracted samples were compared to the results of samples which were not pre-extracted.
Extraction of Tellurium .. If the digested sample was not pre extracted, the solution resulting from the digestion process was subjected to the extract ion process . Since perchlor ic and sulfuric acid remained after the digestion was completed, they were examined for their effect on the extraction process . This was done by adding various amounts of these acids to standard solutions and then subj ect� ing these solutions to the extra�t ion process . The effect of hydrochloric acid on the extraction was examined by a similar method .
A buffer was added to the solut ion to be extracted, This buffer was 5% boric acid, 1% EDTA, ' and 1% KH2P04 . The pH .of the buffer had been adj usted to 8.6. Potassium cyanide was added as a masking agent .
Different amounts of the buffer were added to samples to determine the effect on the extract ion . Samples were extract ed using a buffer with no KH2P04 to determine the effect on the analysis . Potassium cyanide, EDTA, or both were deleted from the extraction process of some samples to determine their effect on the extract ion .
The pH of the solution was adj usted to 8.5-8.8. The effect on the analysis of adjusting the pH with either a NaOH solution or a KOH solution was determined . The pH effect was investigated by performing extractions at select ed pH values between 4.5 and 9.5,
The solution was transferred to a separatory funnel and sodium diethyldithiocarbamate (NaDDTC } was added. Various amounts of NaDDTC were added to the solut ions to determine the effect on the extract ion . 2 7
The solution was then extracted with three successive port ions of carbon tetrachloride . Methylene chloride and methyl isobutyl ketone were also used as organic solvents . The minimum shaking time and volume of organic solvent needed for . complete extraction were determined . The amount of tellurium in each of the three successive portions of the cc14 and in the aqueous solution after the extraction was determined. Sodium perchlorate was added to a standard solution which was to be extracted.
This was done to determine if salting out effects occurred in the extraction. Various metals were added to a standard solut ion to determine
if the tellurium would be extracted in their presence . Corn s __mples were spiked with tellurium to determine if it all would be completely extracted. The size of the corn samples were varied to determine what effect this would have on the extraction or analysis processes .
Treatment of Organic Extracts . The organic extracts were treated by several different means prior to the analysis step . A number of the carbon tetrachloride extracts were concentrated by evaporat ing the solvent on a steam table. The extracts were also concentrated by evaporating the solvent under a vacuum at room temperature . Due to its high volatility, methylene chloride was used for most extracts which were to be concentrated by evaporation under vacuum. Methylene chloride was also used for extracts which were to be completely dried and then redissolved in a mixed solvent. This was done to decrease any matrix effects caused by the organ ic solvent during the analysis step . These solvents included mixed water-ethanol solvents of different concentrations and a mixed water-acetone solvent . The 2 8
tellurium was also re-extracted from the organic extracts using acid ,
nickel nitrate, mercuric chloride , or cupric chloride solutions .
To determine if the organic matrix had an effect on absorbance measurements, the tellurium was place9 into an aqueous media by redigesting the organic solvent . Nitric and perchloric acid were used
for this redigestion . The effect of the perchloric acid on the analysis step was determined by digesting the extracts using various amounts of the acid. The effect of neutralizing the perchloric acid with NaOH prior to the analysis was determined.
The maj ority of the organic extracts were analyzed without any pretreatment .
Analysis of Samples Extracted with NaDDTC . Tqe effect of adding either an acid solution or a nickel solution on top of the organic extract in the furnace was determined . Memory effects within the furnace were determined by analyzing an acid blank aft er analyzing a cc14 extract . The difference between the absorbance readings of CCl4 and aqueous solut ion was checked.
Interference Studies Involving NaDDTC . NaDDTC was added to aqueous standards to determine its effect on the absorbance readings .
The effect of filtering these standards after adding the NaDDTC was also determined . The effect of adding NaOH to standards spiked with
NaDDTC on absorbance readings was ascertained.
Background absorption caused by NaDDTC was determined in several ways . The absorbance on a nearby non-resonant line was determined for 29
a standard spiked with NaDDTC . The standard was also analyzed on the tellurium line without the us e of the background corrector . The background asborbance was examined by analyzing the standard using a lead or zinc lamp . The effect of interrupt ing the gas flow while analyzing standards spiked with NaDDTC was determined .
Extraction of Tellurium with the Iodide System
Extraction of Tellurium . The samples were digested in the same manner as they were for the NaDDTC extractions . The digested samples w�re transferred quantitatively to 150 ml beakers . The pH was adj usted to neutrality with 1:1 NH40H . The white precipitate which forms was redissolved with 1 or 2 drops of dilute hydrochloric acid. Six ml of concentrated HCl was added a�d the total volume of the solution was brought to 70 ml . The hydrogen ion concentration was approximately 1
N. To determine the effect on the background absorption , the solut ion was filtered to remove the insoluble salts . The solution was transferred to a 125 ml separatory funnel and 6.6 g of sodium iodide was added. This made the iodide ion concentrat ion approximately 0.6
N. Less NaI was used to determine if this would decrease the back ground absorption from the iodide ion . Since ammonium iodide has a lower boiling point than NaI , it was used in the latter part of the investigation . Various amounts of NH4 I were used to extract blanks and standards. The effect of this on the background absorption wa s determined.
The tellurium was then extracted with three twenty ml port ions 30
of n-amyl alcohol . An ·ether-amyl alcohol mixture was used as a
solvent to determine its effect on the extract ion . The volume of amyl
alcohol was decreased to ascertain its effect on the extraction . The organic extracts were washed with 1 N HI to determine if this process would decrease the background absorpt ion . Back extraction of tellurium
from the organic extracts into dilut e NH40H was studied . The tellurium
in the organic extracts were analyzed to determine if the digest ion of the extract� was necessary .
The extracts were filtered to remove insoluble salts which remained after the extraction . This was done to decrease the background absorption .
The tellurium was placed into a aqueous media by different methods . The first method involved digest ing .the �xtracts with nitric acid . In the second method the extract solution was dried on a steam table and the residue was redigested , For most samples, the extracts were evaporat ed to twenty ml on a steam table . Twenty five ml of
I remaining alcohol was evaporated, Ten ml of 3% H202 was added and the
was covered with a watch glas s� and the HN03 was added, the beaker solution was heated on a hot plate . When the solut ion no longer appeared oily and was colorless, the wat ch glas s was removed and the solution was evaporated to dryness . The res idue was redissolved in dilute nitric acid and diluted to a volume of 25 ml . It was this solut ion that was analyzed for tellurium .
Ten gram corn samples were spiked with tellurium to determine
The weight s of the samples if all of the metalloid would be extracted. 31
spiked with tellurium were varied to determine the effect on the extraction .
Analysis of Samples Extracted with Na I. The same instrumental and furnace paramet ers were used for the analysis as were used for the analysis of the .samples extracted .with NaDDTC. The slit width, gas flow, atomizing temperature,_ and atomizing time were varied to determine the effect on the background absorbance . The drying temperature was lowered to determine its effect on the analysis of standards . The effect of iron on the telluri1im analysis was det ermined . The concentration of iron in the samples was determined.
The effect of making the samples and standards acidic ( 2 % HN03 ) just prior to the analysis was determined .
Unspiked corn samples were digested and extracted to determine the effect on the background absorbance . Solutions of the reagents used in the extraction were analyzed to determine their contribution to the background absorption . RESULTS AND DISCUSSION
In this sect ion the results which were obtained from ·the experimental procedures are presented .and con clusions derived from the data are discussed. A discussion of the optimum condit ions required for the ashing of the samples is presented. Interferences which , inhibited the extraction and the conditions which were required for the complet� extract ion of the tellur ium using NaDDTC are discussed .
A sim ilar discussion is presented for the extraction of tellurium with the iodide system . The in strumental parameters required to give the greatest sensitivity and interferences which occurred during the analysis are discussed . The various chemical states of tellurium which occurred during the extraction an d analysis process� s are presented.
A summary is given for an extraction procedure and analytical method which is suitable for the determination of trace amounts of tellurium in botanical materials .
Ashing of Samples
The acids used to digest the samples had various efrects on the sensitivity of the Qnalysis . The volume of nitric acid used in the digestion of the samples had little effect on the analysis . If sulfuric acid was used for the digestion, it decreased the absorbance reading by approximately 14%. This interference was eliminated by solvent extraction .
When only nitric and perchloric acid were ·used to ash t e samples, there was a tendency for the samples to ignite. This occurred during 33
the latter stages of the digest ion when perchloric acid was the only acid present . Therefore , it was advantageous to use sulfuric acid whenever possible for ashing ·the samples .
The rate at wh ich the samples were digest ed had little effect on the absorbance readings . Non-digested material or insoluble salts which remained aft er the digest ion decreased the sensit ivity by approximately 4% for 1 _g samples . It was assumed that larger concentrations of insolurrle materials due to larger sample sizes or smaller solution volumes would cause greater int erferences.
Effect of Instrumental Parameters
It was determined that the recorder response time was not a factor in the analysis if the absorbance readings w.ere kept below
0.3 A. If the readings were higher than this , they were decreased by either dilut ing the solution or placing a smaller vo lume into the furnace .
The peak read mode provided the same values which were obtained from the recorder , however the peak read mode is more convenient because the . values do not need to be read from the chart . The concentration mode is similar to the peak read mode and the benefits of its use were not warranted in this investigation. The use of the integration mode was beneficial during the analysis of samples that had matrix constituents which decreased the volatility f the tellurium . Decreasing the volatility caused the peaks to be broader and shorter. The integrat ion mode made it possible to compa e these peaks to the sharper peaks of aqueous standards . This mode was used 34
to analyze standards which were spiked with NaDDTC .
When the charring step was eliminated, the sensitivities of
standard solut ions were decreased by 20%. Figure 1 shows -the effect
of the charring temperature on the se�sitivity . It was found that the optimum furnace parameters which were previously stat ed were suitable for all samples regardless of the matrix. This , of course, excludes the drying temperature which' is dependent on · th� · solvent . The effect of the atomizing temperature on the sensit ivity is illustrated in
Figure 2 .
By interrupting the inert gas flow during the atomizat ion step , the sensitivit ies were increased significantly . In most cases the sensitivities were nearly doubled . Figure 3 shows the effe ct of
interrupting the gas flow on a calibration curve obtained from
standard solutions. It can be seen that although the sensitivities
are increased , the linearity of the curves are not affected,
When the graphite tube was coated with La , Mo , or Zr compounds , the peak heights were reduced, However , the peaks were broader which
indicated that the atomizat ion was occurring at a slower rate. By
integrating the peak area instead of measuring the peak height , the sensitivities were found to be the same for the treat ed and the untreated tubes . It was found that during the analysis of the organic extract s, integrating the peak height s for ten seconds gave more precise results than when an integrat ion period of three seconds was used. When analyzing aqueous solut ions , the precision was the same for both time periods . This would indicate that the tellurium in the 35
Figure 1
Effect of Charring Temperature on Sensitivity
0 .125
0.100
(1) 0. 075 C) � ro ,..Q �
Ci)0 �
0.050
0.025
200 400 600 800. 1000
Charring Temperature ( 0c) 36
Figure 2
Effect of Atomizing Temperature on Sensitivity
0. 125
0. 100
0.075
0.050
0. 02 5
2000 2200 2400 2600 2800
Atomizing Temperature (0c ) 37
Figure 3
Effect of Argon Gas Flow on Calibration Curves
0.40
Gas Flow Interrupted
0.30
Gas Flow Normal
QJ 0 fJ .Q 0.20 M 0 Cll �
0.10
0.25 0. 50 0. 75 .1 • 00. 1.25
Na�ograms of Tellurium 38
organic extract is atomized at a slower rate than in an aqueous media .
Although it is not detectable, this same phenomonum is probably occurring
in untreat ed tubes. If aqueous standards were used during the
analysis of organic extracts, the long.er integrat ion period was used
in order to obtain accurate results.
If a single solution was to be analyzed several times, the
disposable pipet tip was used more than once . It was found that
reusing the_ tip had littl� effect on the precision of the analys is .
Analysis of Standards and Blanks ·
Boiling ch�ps did not contribute to the absorbance of the blanks .
Throughout the investigation there were differences between the
sensitivities of standards which contained acid and those which were non-acid. The standards containing acid read higher than the non-acid
standards during 70% of the runs . The sensitivities of the acid
standards averaged 15% higher than those of the non-acid standards .
When the non-acid standards read higher than those of the acid
standards, the sensitivities averaged 10% higher . It was originally
assumed that because of the low concentration of tellurium in the
standards, adsorption of the metalloid onto the glassware would
significantly decrease the concentrat ion of the solut ion . It was
reasoned that adding acid to the standards would prevent this
adsorption from occurring, however, this does not explai. the lower readings of acid standards in some cases. To determine if adsorption
was occurring , non-acid standards were allowed to set several days before the analysis . These standards gave the same absorbance as 39
standards which had been freshly prepared . This would indicate that
adsorption was not the cause of the problem .
The concentrat ion of acid · in the standards had little effect on
the sensit ivity except at levels higher than 4% acid. The effect of
the acid concentrat ions on the sensit ivity can be seen in Figure 4 . It
was concluded that high concentrat ions of acids caused interference
during the analysis .
It can be seen in figure 4 that there is a slight difference in
the sensitivities of standards made with different acids . To determine
if the an ion present in the acids were the cause of these differences,
the same an ions were added to standard solut ions in the form 0£ salts.
The effect 0£ the nitrate ion was not checked, however the effect of
. the sulfate ion was determined . It was found that the solutions
containing the salts had sens itivities which were �4% less than the
readings of the acid solutions .
. The conclusion reached was that the differences between the acid
and non-acid standards were caused by a combination of physical an d
chemical effects such as molecular absorption or the forma tion of nonvolatile species . At higher tellurium concentrat ions these effects might not be detectable .
The calibration curve of standards in an EtOH : 1% HCl04 solvent
rations than f showed a deviation from linearity at lower concent or
seen in Figure 5 tha the aqueous standards (Figure 5) . It can also be t
lower than for aqueous sensitivity for ethanolic standards is much standards . 40
Figure 4
Effect of Ac id Concentration on Sensit ivity
0.125
0.100
0.075 Q) 0 s::.:: rO ,.Q H 0 (/) ,.Q �
0.050
0.025
1.0 2.0 3.0 4.Q
Acid Concentrat ion ( % V /Y ) 41
Figure 5
Compariso of Calibration Curves for Ethan :· lie and Aqueous Standards
0.3 q Aqueous
0.3 0
0.25
Q) (.) � ro ..Q H 0.20 0 (/) :i1
0.15
0.10
Ethanolic
0.05
1.6 0.4 0.8 1.2
Nanograms of Tellurium
ft 4 2
The absorbance readings obtained from the standards and samples
should be dependent on the total weight of tellurium placed in the
furnace. To affirm this , calibration curves were obtained by two
different methods . Equal volumes of standards of different
concentrations were placed in the furnace to acquire one plot (Figure
6) . Different volumes of single standard were also placed in the
furnace and a second plot was obtained (Figure 7) . It can be seen that
both plots �re linear , however the slopes of the curves are different .
To determine the reason for this difference , several calibration plots
were· obtain ed us ing different volumes of a series of standards
(Figure 8). As the concentrat ion of the standards increased the slope
of the calibrat ion curve decreased . Although the reason for this
phenamona is unknown , it was found that modifying the matrix of the
solut ion with a nickel compound eliminated the difference in the
slopes . Figure 9 is a series of calibrat ion curves obtained from
standards to which 20 ppm of nickel was added.
Several times when analyzing large volumes (100 ul ) of standards ,
the quartz windows on the ends of the furnace had a tendency to cloud .
At other times i� was not unusual to obtain low absorbance readings / or no readings at all. When the window clouded, the furnace would
crackle during at omization . During a single run it was found that one
new graphite tube gave good results, but when a second new tube was
used the windows would cloud and poor results were obtained. This would tend to indicate that the problem arose from differences in the
the . graphite tubes or in the posit ioning of the tube in furnace The 43
Figure 6
Calibration Curve for Constant Volume with Varying Concentration
0.2 5
0.2 0
Q) 0 0 .15 � ..Q H 0 Cl) �
0.10
o.os
0.5 1.0 1.5 2.0 2.0 2.5
Nanograms of Tellurium
- 44
Figure 7
Calibration Curve for Constant Concentration with Varying Volume
0.3 5
0. 30
0.2 5
Q) 0 i:: � 0.2 0 � 0 (/) �
0 .15
0 .10
o.os
2 .0 0.5 1 . 0 1.5
·Nanograms of Tellurium 45
Figure 8
Calibration Curves for utandards of Different .Conce;,1 t...:3·i:..LO us in au A';_uc:ms Solvent
0.2 8
0.24
0.20 2f: ppb
') ppb Cl.I u � / ro 0.16 .Q H 0 (/) I � I
0.12
0.08
0.04
2.0 2 . 4 0.4 0.8
Tellurium Nanograms of 46
Figure 9
Calibration Curve for Standards of Different Concentrations in an Aqueous Solution Containing 20 ppm Ni
0.3 2
0.28
0. 24 10 ppb
Cl) () s:: rd ..Q �-I 0 Cf) �
o.o
1. 5 2.0 0. 5
Nanograms of Tellurium 47
first possibility is unlikely because the tubes are manufactured to
exact specificat ions . The second possibility is also unlikely because
there is a potential of only a small variat ion of the position of the
tube in the furnace . To check this possibility , a tube from which poor
results had been obtain ed was repositioned several. times in the furnace.
The reposition ing had no effect on the results. It was also thought
that the clouding of the windows arose from an insufficient flow of
the inert g�s through the furnace. The inert gas enters the furnace
on the ends and leaves through the sample port thus carrying all
vaporized material away from the windows . The gas flow was increased
but this did not effect the interference . The pyrolytic coating was
removed from the graphite tube to 4etermine if this would eliminate
, the problem but it had no effect. The use of nickel compounds to mo�ify the matrix of the standards increased the sensit ivity and eliminated the clouding of the windows , however these improvements were not repeatable from day to day .
At this time there is no explanat ion for the cause of this interference , however it appears to be related to the matrix of t .e
. standards and to some phys ical property of the graphit e tubes
Extraction of Tellurium with the NaDDTC System
tellurium is generally Pre-Extraction with Cupferron . Since
low concentrations , other present in biological materials in extremely
quantities will interfere with the metals wh ich are present in greater
metals interfere because they extraction of the tellurium . These 48
form com plexes with the Na DDTC thus decreasing the amount of the
chelat ing agent which is free to complex with tellurium .
Bismuth, ant imony (II I), thallium (II I), and copper were pre-
extracted with cupferron prior to the extraction of tellurium with
NaDDTC . These metals will also form colored complexes with NaDDTC and
will interfere with the analysis if the tellurium is to be determined
by photometry. This interference is of little concern when the
tellurium is to be determined by atomic absorption .
The amount of cupferron us ed for t�e pre-extraction of standard
solut ions was inversely related to the amount of tellurium found during
the analysis . As seen in Figure 10, the amount of tellurium extracted
drops sharply as the amount of cupf�rron us ed for the pre-extraction
increases . This indicates that some of the tellurium was lost during
the pre-extract ion .
Various weights of samples were spiked with equal amounts of
tellurium and pre-extracted with equal amounts of cupferron. Fifty-
four percent more tellurium was extract ed from a ten gram sample than
from a five gram sample. It could be concluded that if large a�ounts
of metals other than tellurium are present , the cupferron will complex
urium. with those metals before it complexes with the tell
from the pre -extraction Both the organic and the aqueous phases of
The organic phase was redigested standards were analyzed for tellurium .
media prior to the analys is . This to place the tellurium in an aqueous
redigested organ ic. phase. The solut ion will be referred to as the
· an nd a had a lower reading th sta ards aqueous p h ase f rom the extr-ct ion 49
Figure 10
Effect of Cupferron Concentrat ion on the Amount of Tellurium Extracted
35
30
'"d Q) .µ 0 ro 25 H .µ x µ:i § .,, � � 20 � Q) f-i 4--1 0 .µ � 15 Q) 0 H Q) p..
10
5
0.12 0.1 6 0.04 0 . 08
Cupferron (%) Concentration of 50
of equal con centrat ions , however this may be due to interferences
caused by high salt concentrat ions in the solut ion . When the redigested
organic phase was analyzed a large negative peak occurred� This was
probably caused by overcorrect ion by the background compensator of
interferences caused by the ac ids used to redigest . the extracts.
Before the negative peak there was a positive peak . This peak had
approximately on e tenth the height of the peak which was obtained from
the aqueous phase . The positive peak was probably caus ed by tellurium
which would again indicat e that tellurium is being removed in the
pre-extraction step . This would cause a low reading when the final
analysis is made .
The analyt ical results of samples which were pre-extracted were
compared to samples which were not . It was determined that the
advantages of the pre-extract ion were not great enough to continue its
use for the extract ion of standards and small sample weights (less than
5 g). Th ese had small amounts of interfering metals . The pre-
extraction was used for larger (10 g) samples.
Extraction of Tellurium . The effect of hy drochloric , nitric,
was determined . sulfur ic, and perchloric acid on the extract ion It
from standard solut ions, was found that when tellurium wa s extracted
ion (Table 1). Small amounts hy drochloric acid inhibited the extract
· 2 · 0%) enhanced the extraction but larger o f perch loric aci·d (le ss than cement occurred with · The greatest enhan amounts inhibited it ( Tabl e 1)
trat ion s of nitric acid or sulfuric a con centrat ion of 0.5%. Concen
ted the extraction. acid greater than 2% also inhibi 51
TABLE 1
EFFECT OF ACID CONCENTRATION ON THE AMOUNT OF
TELLURIUM EXTRACTED
Percent Percent Acid Tellurium Extracted Tellurium Extracted Concentrat ion (%) From HCl Solution From HC104 Solution
0.0 0 77.8 77.8
0.05 95.1
0.10 55.3 94 .9
0.5 0 62 .7 100.0
1. 00 62.3 90.2
2.00 87.1
4 .00 77.5 52
The effect of buffers and various masking agents on the extraction
was determine d. The amount of buffer added to the solution varied from
0. 01% to 0.04% . As the amount of buffer increased, the amount of
tellurium which was extracted decreased (Figure 11 ). If no buffer
was used, the amount of tellurium which was extract ed decreased
(Figure 11 ). The presence of 1% potassium dihydrogen phosphate in the
buffer increased the extraction of the tellurium by approximately 22%.
The amount of tellurium extracted was increased 18% by using EDTA
as a masking agent . If the extraction was performed at a pH of 6.5, the addition of KCN improved the extraction by 14% but at a pH of 8.5,
KCN decreased the extract ion approximately 10%.
The extract ion was performed at selected pH values betwe en 4.5 - . 9.5. If no masking agents were used , the pH had llttie effect on the extract ions . If masking agents were used, the extraction was improved at a low pH .
Using either KOH or NaOH to adjust the pH had no effect on the extraction or the analysis .
It was found that the amount of NaDDTC used to extract the tellurium needed to be carefully controlled . Enough of the chelat ing
h all agent was needed to complex with the tellurium and also wit metals
ion . If insufficient which compete with tellurium for chelate format
would not be extracted. If amounts were added , all o f t h e t e 11ur ium
erferences within the furnace excess NaDDTC wa s added, it caused int during the analysis process.
ne chloride, and methyl isobutyl Carbon tetrachloride, methyle _ 53
Figure 11
Effect of Buffer Concentration · on the Amount of Tellurium Extracted
100
ro (]) +J () ro H +J x 80 µ:i
·�§ � r-i r-i (]) 60 E-4 4-i 0 .µ � Q) () 40 � Q) p....
20
0.01 0. 02 0.0 3 0.04
Buffer Concentration (%)
, 1% EDTA , and 5% boric acid . Buffer contains 2% KH2Po4 54
ketone were used as organic solvents in the extract ion . Unless a
particular solvent is specified , all results reported here were
obtained using carbon tetrachloride as the organic solvent . When
methylene chloride was us ed , the absorbance r'eadings were about one
half of those obtained when us ing carbon tetrachloride . This decrease
was assumed to be due to matrix effects in the furnace and not due
to incomplete extraction of the tellurium . The evidence for this
assumption will be discussed later. When placing the methylene chloride
extra cts in the furnace , keeping the extracts in the pipet during the · transfer was a problem . The readings obtained when using methyl
isobutyl ketone as a solvent were 27% less than those obtained using
It was determined that one minute was the minimum shaking time
needed for complete extract ion when using CCl4 as a solvent . The minimum volume of cc14 needed for complete extraction was ten ml per extract ion when three successive extractions were completed on a single sample .
When each of three successive extracts were analyzed for tellurium the first extract contained 87% of the extracted tellurium ; the second extract con t aine· d 12�o,· and the third extract contained 1%.
The aqueous solution which remained after the extraction was analyzed
g for tellurium . From that Solution an absorbance readin was obt ined which would indicate that One third of the original amount of tellurium
Wa s assumed that this reading was caused has not been extracte d · It
· · the solution and not due to tellurium . by a high salt concentration in 55
This was confirmed by analyzing blank solutions that contained 1%
NaCl or 1% NaCl04 . The absorbance readings obtained from these blanks
were 1 2 - 22% of the readings obtained from standard solutions .
Various amounts of Na Cl04 were added to the tellurium solution
to determine if salting out effect s were occurring during the
extraction . The salt had little effect on the extraction efficiency .
Tellurium was extracted fr.om a solution containing· 0 . . 1 ppm Te and
10 - 100 ppm Cu . It wa s found that only 14 - 24% of the tellurium was extracted . This is significant because �iological samples generally have much higher concentrat ions of other metals than of tellurium
It was found that 3 ml of a 10% NaDDTC solut ion was needed to extract the tellurium from corn samples which were spiked with tellurium . Less than 0.5 ml was needed to extract the tellurium from a standard solution of the same concentration .
Treatment of Organic Extracts . When the organic extracts were concentrat ed on a steam table , 30 - 60% of the tellurium was lost .
The decrease in tellurium appears direct ly related to the concentrat ion of the solut ion (Figure 12 ). When the extracts were evaporated under vacuum , the absorbance readings of those samples were 10% lower than what they should have been .
ic extract s were To eliminate matrix effects , the organ evaporated
This residue would not completely and the residue was redissolved .
e was dried in an oven at 1 2 0°c for redissolve in water . The residu
components, however it still would not two hours to drive off organic
sary to use a mixed solvent which dissolve in water . It was neces 56
Figure 12
Effect of The Solution Concentrat ion on 0.9 Tel lu�ium Lost Duri�g Evaporation of Organic Extracts
0.8
0.7 9' •ri � r-1 r-1 Q) 0.6 f-i 4-1 0 � 0 .,; .µ 0.5 n:1 H .µ � Q) u � 0 u ' 0.4 Q) u � n:1 ,.Q H 0 (/.) ,.Q 0.3 ct:
0.2
0.1
4 0.6 0.8 1.. 0 1.2 0.2 0. m (ppm) Concentrat ion of Telluriu 57
would dissolve the residue but wh ich would not introduce matrix effects during the analysis . The solvents used were water-ethanol solvents and a water-acetone solvent . The solvent s in increasing order of solubility of the residue are : H20 < 1:1 Et0H-H2o < 1:1 acetone-H2o <
100% EtOH . Unfortunately the same order applied to increasing matrix effect s within the furnace . The ·solvent chosen to be used was a 1:1
Et OH - 1% HCl04 solut ion . The perchloric acid was added to decrease adsorption of the metalloid onto -the glassware . The effect of this solvent on standard curves has been discussed .
A number of experiment s were performed in which the organic extracts were dried and then redissolved in a mixed solvent. The experiments had been previously completed using either an aqueous solvent or an organic solvent . These experiments included determining the effect of the pre-extraction of interfering metals prior to the extraction ; the effect of masking agents on the extract ion ; and the effect of using different amounts of NaDDTC on the extract ion . The result0 of these experiments confirmed those previously described in which organic or aqueous solvents were used .
Tellurium was back extracted into solut ions of various metal ions .
It was found that 13. 5% of the tellurium was extract ed into a 10%
Ni(No3 ) 2 solution , 75.5% of the tellurium in the organic solvent was extracted into a. saturated HgCl2 solution and 31.6% of the tellurium wa s extracted into a 10% CuCl2 solution .
When the organic extracts were redigested to place the tellurium
was n in an aqueous media, an absorbance reading obtai ed which was the 58
same as a stan dard of equal concentration . This $upported the evidence
that all the tellurium was being extracted and that matrix interferences
were being caused by the organic solvent during the analysis . Carbon
tetrachloride or chloroform was used as the organic solvent for the
extraction.
If the acid used to redigest the extracts was neutralized with
NaOH or KOH before the analysis , the absorbance was decreas ed 24 - 68%.
The amount of perchloric acid used to redigest the organic extracts
had the same effect on the analysis as it. did for digested samples which were not extracted . If the amount was kept to a minimum , the acid had little effect on the an alysis .
Analysis of Samples Extracted with NaDDTC . T�e carbon tetra- chloride extracts proved to cause a broad band background absorption .
It was shown that the background compensator completely corrected this absorption .
By adding a 4% perchloric acid solution or a 100 ppm NiN03 solut ion on top of the organic extracts in the furnace , the signal was enhanced by 30%.
No signal occurred from an acid blank which was run after a
we carbon tetrachloride extract . This would indicate that there re no
ing from the organic memory effects occurring in the furnace result
matrix decreased the matrix . As implied previously , the CC14 sensitivity of the analysis .
a flame system , it was found When samples were analyzed with
extracted with cupferron gave the same that samples wh ich had been pre- 59
absorbance readings as the standards . Samples which had not been
pre-extracted read 60 - 70% lower than the standards . This affirmed
the necessity of the pre-ext raction process for samples with high metal content . Samples dissolved in a 1:1 EtOH-1% HC104 solvent
had low sensitivities during the flameless analysis_, however samples
dissolved in the same solvent had no reduction in sensitivities when analyzed with the flame system . It was concluded that the · solvent was_ causing interferences within the furnace.
Interference Studies Involving Na DDTC . To determine if t�e chelating agent was causing interference with the analysis , standards were spiked with NaDDTC prior to analysis . It was found that a concentration of 0.0025% NaDDTC decreased the sens�tivity by one third . Increasing the concentration of the NaDDTC did not significantly increase the interference . The furnace parameters were optimized for the standards containing the NaDDTC but this did not reduce the interference . By increasing the pH of the spiked standards the int erference was decreased by 20%. Filtering the standard containing the ,NaDDTC had no effect on the interference . The inter ference was not decreased by interrupting the inert gas flow during the atomizing step. Broad band background absorption caused by the
NaDDTC was checked by analyzing the spiked standards using a zinc or lead hollow cathode lamp . All analyses with the zinc lamp gave igh readings which were assumed to be caus ed by zinc in the NaDDTC. A high reading was obtained for a tellurium standard spiked with NaDDTC when analyzed using a lead lamp , however , standards which were 60
extracted had no readings . It was concluded that the NaDDTC caused broad band background absorbance but this interference was essentially eliminated by the extraction process . ·
Extraction of Tellurium with the Iodide System
Extraction of Tellurium . Removing the insoluble salts by filtrat ion following the pH adj ustment increased the ·sensitivity of the analysis by 8%. The removal of these salts was assumed to increase the extraction efficiency .
It was assumed that interferences which occurred during the analysis step was also part ially due to salts which were carried through the extract ion . Several methods were attempted to remove these salts . Using an ether-pentanol solvent to provide a cleaner extraction reduced the interference by 2%. Filtering the organic extracts or washing the extracts with hydriodic acid slightly decreased the background absorption . It was felt that the combination of all three of these methods did not diminish the interference sufficiently to warrant their continued us e.
Reducing the amount of n-amyl alcohol used in the extract ion by one half decreased the time needed to digest the organic extracts ,
lurium was co however , only one third the amount of tel re vered.
ted Essentially no tellurium was back extrac into dilute ammonium
the tellurium was lost when the hydroxide . Approximately one half of
with nitric acid . Drying the extracts organic extracts were digested
dissolving the residue in acid also resulted on a steam table and then 61
in the loss of 24% of the tellurium .
Analysis of Samples Extracted with Iodine . Corn samples which
were spiked with tellurium were extracted and it was found that
essentially all of the tellurium was recovered. The sample mass was
varied and it was affirmed that the amount of matri.X constituents from
the samples had little effect on the -analysis (Table .2).
It was found that adding acid to the sample and standard
solut ions just prior to the analysis had no effect on the results .
No unusual analytical problems occurred in the determinatjon of
tellurium in samples which were extracted with iodine except for
broad band background absorption caused by iodide . This interference
is discussed in the following sect ion .
Interference Studies Involving Iodide . When the sample solutions
were analyzed, a large amount of background absorption occurred. The
background compensator had a tendency to overcorrect this absorption
resulting in negat ive deflect ions on the recorder. Many times these
negat ive deflections were of greater magnitude than the positive
deflections caused by atomic absorption . If the instrument was in
the peak read mode when this occurred , the value obtained was that of
. the negative deflect ion and not of the posit ive It was assumed that
interference caused this interference was due to broad band by the
stead of sodium iodide did not iodide ion . Using ammonium iodide in
was recovered nor did it reduce reduce the amount of tellurium that
u little as 2 0% of the NH4 I that a (14) the interference . sing as H nson 62
TABLE 2
EFFECT OF SAMPLE MASS ON THE AMOUNT OF TELLURIUM EXTRACTED
Sample Mass (g) Tellur ium Recovered (%)
3 97 .6 % ± 16.70 %
6 100 . 0 % ·± 9.50 %
10 95.2 % ± 15.50 % 63
used in his method decreased the extract ion of the tellurium by less
than 10%. Using smaller amounts of NH4I decreased the interference
only slightly .
It was reasoned that a more vigorous digestion of the organic
extracts would oxidize the iodide to iodine which could then be
evaporated . It was attempted to use sulfuric acid as an oxidizing
agent , however as previously discussed , this decreased the sensitivity
of the analysis . The digest ion period was increased using only HN03
and H202 as oxidizing ag ents . This decreqsed the amount of the back-
ground absorption to a large extent .
Acid blanks which were digested and extracted had a high back- ground absorbance which was also pro�ably due to the iodide ion . If the extracts were extens ively digested the backgrou�d compensator effectively eliminated this interference . Blanks containing HI , HN03 , or NaI were analyzed . Again negat ive peaks were recorded indicating overcorrection of background absorbance by the background compensator .
This effect was more pronounced for the NaI blank than for the HI blank .
Comparison and Summary of Methods
of act n The diethyldithiocarbamate and the iodide methods extr io
was more effective for the were compared to determine which method
ma terials . The NaDDTC met od extraction of tellurium from botanical
therefore eliminat es interferences prov1· d es a c 1 eaner extraction and
, the extraction efficiency is caused by insoluble salts . However chelate format ion. � wh ich compete for extremely sens1• t ive· +0 metals 64
Although a pre- extraction step and masking ag ents ar e us ed , it is
difficult to obt ain quant itative extract ion of the tellurium . The
iodide method is less susceptable to interferences caused by competing
metals . Although the extraction is not as clean ·as the NaDDTC
extraction , interferences caused by insoluble salts can be minimized
by a proper extraction technique .
The overall time required for the extraction is generally less
for the NaDDTC method , however the time required to do the actual
extraction is considerably less for the iodide method . The maj or
portion of time required by the iodide method is involved in the
evaporat ion of the organic solvent . Since other extractions may be
completed during this time period , the iodide method is actually the
least time consuming method . Because the iodide method is less time
consuming and is less susceptab le to interferences , the following
procedure was concluded to be effective for the extraction an d
determinat ion of tellurium in biological samples.
Ten grams or more of sample is wet ashed with 50 ml of nitric
acid to remove all eas ily oxidizable material . When the evolut ion of nitrogen oxides decrease, 1.5 ml of sulfuric acid and 1.5 ml of perchloric acid are added. The digestion is continued until perchloric
sample occurring . If acid fumes appear with no charring of the
and the digest ion is charring occurs more nitric acid is added
ashed , the solution is continued . After the sample is completely
is adj usted to 7 with 1:1 NH40H. trans f erre d t o a beaker and the pH .
I are then added and the solut ion is Six ml of HCl an d 6.6 gr of NH4 65
transferred to a separatory funnel . Water is added to increase the
solut ion volume to 70 ml . The solution is then extracted with three
successive 20 ml port ions of n-amyl alcohol . The organic ' extracts are combined in a beaker and evaporated to a volume of 20 ml on a steam tab le . Twenty-five ml of 3% H202 is added and. the remaining alcohol is evaporated . Distilled water can be added to keep the aqueous layer at a volume of 15 ml . After the alcohol is evaporated , ten ml of distilled HN03 is added , the beaker is covered with a watch glass , and the solution is digested unt il .it is colorless . The watch glass is then removed and the solut ion is allowed to evaporate to dryness . The beaker is allowed to cool after which 0.5 ml of HN03 and
5 ml of wat er are added . The solutio.n is then transferred quantitative ly to a 25 ml volumetric flask . A nickel nitrate solution is added to the flask so that the final solut ion will be 20 ppm Ni . The flask is filled to volume with distilled water . Ten to one hundred microlit ers of this solut ion is placed in the graphite tube furnace . The smallest volume should be used whenever possible . The furnace parameters are : 0 drying temperature - 1so c; charring time - 30 sec ; charring temp�r ture
- 2 0°C . - soooc; atomizing time - 7 sec; atomizing temperature 70 The
ace during the atomizat ion inert gas is allowed to flow through the furn
ctor should be used throughout step . The deuterium arc background corre
should be 2 % HN0 and have a the analysis . The tellurium standards 3 concentrat ion of 20 ppm Ni .
Chemical States of Tellurium
of both TeI4 and K2TeI 6 have been reported , Although the extraction 66
it was concluded that the complex extracted in our method was either
Na2TeI5 or (NH4 ) 2TeI5. The complex which was formed was dependent on
the cation present in the chelat ing agent used in the extract ion .
During the oxidation of the organic extract , the complex was hydrolyzed
to either tellurous acid (H2Te03 ) or to orthotelluric acid (Te(OH)6).
When the digested solution was evaporated to dryness these acids were
dehydrated to form Te02 . A tellurium dioxide solut ion was formed when
the residue was dissolved and it was this solut ion that was placed into
the furnace for analysis . After the solv�nt was evaporated, Te02
remained in the furnace . Three different forms of tellurium may have
been produced during the charring step . The tellur ium dioxide may have
been reduced by the cai�bon of the gr�phite tube forming the elemental
state as illustrated by react ion (1).
(1) +
The carbon of the furnace may also have reacted with the Te02 to form a carbide .
( 2 ) +
of 1 245°C , may e The tellurium dioxide , which has a boiling point hav
. When the furnace was coated remained intact during the charring step
, or Mo ), thus separat ing tne with a carbide forming element (La, Zr
surface , the sensit ivity of the analysis was Te02 from the carbon the carbon does indeed interact reduced. This would in dicate that
l. f a carbide was being formed (react ion with the tellurium . However , 67
2 ), it would presumably be more stable than the oxide and therefore coating the furnace should have increased the sensitivity . It was concluded that at least a part ial reduction of Teo2 (react ion 1) occurred during the charring step . CONCLUSION
In this investigation two methods for the extract ion of tellurium
from botanical materials have been studied . In conjunction with this
study , the determination of tellurium by flameiess atomic absorption
spectrometry has been investigated. The iodide system proved to be
the most effective method of extraction because it was less susceptible
to a decrease in the tel lurium extractior1 by interfering metals .
If the sample solut ion is placed in a small volume aft er the
extraction , the detection limit will be improved, however this will
also increase the concentration of inorganic impurities which will
decrease the sensit ivity of the analysis . Therefore , if the
concentration of tellurium in the original sample allows , the final
solution volume should be as large as possible .
The sensit ivity of the analysis was 0.02 ng for 1% A. The
detection limit was 0. 5 ng of tellurium per one gram of the original
sample . The samples used in our investigation may be considered to
be typical botanical samples which are not exposed to elevated levels
of tellurium . No tellurium was detected in the samples , therefore if
tellurium was present , it was in levels which were below our detect ion
limits .
It is concluded that the iodide method outlined in the preceding
ermination of telluriu in sect ions is an effective method for the det
osed to elevated levels of botanical samples wh ich have been exp tellurium . LITERATURE CITED
Ro senfeld , I. and Beat� , O.A. , "$elenium Geobotany , Biochemistry , Toxcity , and Nutritio_ n ," Academic Press, New York , N.Y. (1964).
2. Trotman-Dickenson , A.F., "Comprehensive Inorganic Chemistry ," Pergamon Press, New York , N.Y., 1973, pp . �35-975 .
3. Havezov , I. and Stoppler , M. , Z. Anal . Chern. , 258 , 189 (1972 ).
4. Busev , A.I. , "Rare Elements ," Ann AX'bor-Humphrey Science Publish ers , Ann Arbor , Michigan , 1970, pp . 321-322.
Brow s. ning , E. , "Toxicity of Industrial Metals ," Butterworth and Co . Ltd. , London , England , 1960� pp . 310-311 .
6. Gladney , E.S. and Rook , R.L. , Anal . Chem. , 47, 1 554-1 556 (1975).
7. Karger , B.L. , "An Introduction to Separation Science ," John Wiley and Sons , Inc. , New York , N.Y. , 1973 , p. 248 .
8. Makarov, V.A. and Mishustina , A.G., Tr . Stavrop . Skd . Inst ., 3(36), 147-149 (1973).
9. Cheng , K.L. , Talanta, 8, 301-312 (1961). l
10 . Bode, H. , Z. Analyt . Chem. , 142, 90 (1955).
11 . Luke , C.L., Anal . Chem. , 31 , 572-574 (1959).
12. Guseinove , I.K. , Bagbanly , I.L. , Vagbanly , S.I., and Rustamov , N.Kh. , Dokl . Akad , Nauk. Azerb . SSR. , 27 , 29-33 (1971).
13 . Busev , A.I., Babenko , N.L. , and M.N. Chepik , ZhAKh ., 19, 871 ( 1964) .
29, 1204-1206 (1957). 14. H an son , CK• . , Anal . Chem. ,
15. Willard , H.H. , Merrit , L.L. , and Dean , J.A. , "Instrumental Methods of Analysis ," fifth ed . , D. Van Nostrand Company , New York , N.Y. , 1974, pp . 350-359.
16. Slavin , M. , "Atomic Absorption Spectroscopy ," second ed. , John Wiley and Sons , New York , N.Y., 1978 , pp. 64-66 .
. Abs . News!., 13 , 123-124 17 . Cheng , J.T. and Agnew , W.F. , Atomic (1974). 70
18. Charabarti, C.L. , Anal . Chim . Acta. , 39 , 293-299 (1967).
19 . Beaty , R.D. , Anal . Chem. , 45, 234-238 (1973).
20. Marvec , M.V. , Kinson , K. , and Belcher , C.B. , Anal . Chim . Acta. , 41 , 447-451 (1968 ).
21 . Chao T.T. , , Sanzolone , R. , and Hubert , A.E. , Anal . Chim Acta. , 96, 251-257 (1968).
22. Fiorino , J.A. , Anal . Chem. , 48 , 120-125 (1976).
23. Watterson , J. , J. Res . U.S. Geol. Surv. , 3, 191-195· (1975).
24 . Campbell, W.C. and Ot taway , J.M. , Talanta, 21 , 837-844 (1974).
25. Sturgeon , R.E. , Chakrabarti, C.L. , and Langford , C.H. , Anal . Chem. , 4 8, 1792-1807 (1976).
26. Runnels , J.H. , Merryfield , R. , and Fisher , H.B., Anal . Chem. , 47, 1258-1 263 (1975).
27 . Smeyers-Verbeke , J. , Michotte , Y. , Van den Wi;ikel , P. , and 48 , 125-130 C 197 6). Massart , D. L. , Anal . Chem.," .
23. Julshamm , K. , Atomic Abs . Newsl ., 16, 149-150 (1977).
29. Ediger , R.D. , Atomic Abs . Newsl ., 14 , 127-130 (1975).
30. Regan , J.G.T. and Warren , J. , Analyst , 101 , 220-221 (.1976).
31. Welcher , G.G. , Kriege , O.H. , and Marks , J.Y. , Anal . Chem. , 46, 1227-1231 (1974).
32. Hubert , A.E. , U.S. Geol . Surv. , Prof. Pap. , 750, .188�.190 (1971).
33 . Hubert , A.E. , U.S. Geol . Surv. , Prof . Pap. , 750, 162-164 (1971).
34 . Bovay , M. and Marcantonatos , M., Anal. Chim . Acta. , 80 , 180-182, (1975).
35. Mashukov , A. ya . and Maslakova , T.G. , Sbornik trudov VNIITsVETMET , No . 5, 98, Metallurgizdat (1959).