DOCSLIB.ORG

Selective-Ultratrace Detection of Metal Ions with SERS Keith Carron

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Selective-Ultratrace Detection of Metal Ions with SERS Keith Carron Selective-Ultratrace Detection of Metal Ions with SERS Keith Carron Ken Mullen . MarkLanouette Helena Angersbach 1991 Journal Article WWRC-9 1- 14 In Applied Spectroscopy Volume 45 Keith Carron, Ken Mullen, Mark Lanouette and Helena Angersbach Department of Chemistry University of Wyoming Laramie, Wyoming Selective-Ultratrace Detection of Metal Ions with SERS KEITH CARRON,* KEN MULLEN, MARK LANOUETTE, and HELENA ANGERSBACHt Department of Chemistry, University of Wyoming, Laramie, Wyoming 82071-3838 We report the results from experiments involving the detection of metal Our goal in this study is to show that it is possible to ions with a Surface-Enhanced Raman Spectroscopic indicator (SERS overcome the hinderance of electrochemical SERS probes indicator). Comparisons of metals showed that the SEW effect can be by utilizing an adsorbed indicator to chelate the analyte used to selectively detect metal ions according to their ionic radius. We with the surface. We also demonstrate the sensitivity . determined a resolving power for separating the alkaline earth series. The results indicate that the resolving power of the SERS approach is advantage of using a resonantly enhanced indicator to superior to that of absorption spectroscopy. Quantitatively, under our signal the presence of a nonresonant analyte. experimental conditions, we found a detection limit of 270 ppb for Pb2+ and 85 ppb for Cu2+with the indicator Eriochrome Black T. Index Headings: SERS; Ultrasensitive detection; Metal ions; Instru- EXPERIMENTAL mentation, Raman spectroscopy; Lasers; Eriochrome Black T. The SERS substrates were fabricated from 1-in. glass squares cut from microscope glass slides. The slides were initially cleaned with concentrated ammonium hydrox- INTRODUCTION ide, then rf sputtered with a Harrick PDC-3XG plasma Surface-Enhanced Raman Spectroscopy (SERS) has cleaner to remove any remaining impurities. The SERS been shown to be an ultrasensitive technique.'-, The ul- surface was produced by depositing 250 nm CaF, (op- trasensitivity has been utilized in the spectroscopic study tical-grade CaF,, Aesar) and 50 nm Ag (99.99 % , Aldrich) of monolayer and submonolayer quantities of organic at 4 x mbar using an Edwards E306A Vacuum compounds, organometallic compounds, and inorganic Coating System. The substrates were stored under vac- anions on metal surfaces. Examples of analytical appli- uum in the coating unit until they were used for spec- cations of SERS are the trace detection of dyes4 and troscopy. nucleic acids? One important class of compounds which Eriochrome Black T (80% pure, Aldrich) was purified has not been detected by SERS is metal ions. Metals by recrystallization of the dimethylammonium salt. This ions are challenging since as a single atom they do not procedure was found to be necessary to obtain good re- possess a vibrational spectrum and, therefore, cannot be sults and is outlined in Ref. 11. All solutions were pre- directly detected with Raman spectroscopy. pared with Millipore water or spectral-grade acetone With the current interest in remote fiber-optic sensors, (Baker). All aqueous solutions were buffered to pH 9 the ultrasensitivity of SERS is being explored as a pos- with NH4C1or NaHCO,. sible spectroscopic technique for optical fiber sensors. Raman spectra were collected and stored with a 386 Direct detection of the analyte has been the scheme pro- microcomputer interfaced to a Jobin-Yvon Mole 1000 posed for the current SERS-based fiber-optic sensors. double monochromator, a thermoelectrically cooled RCA Examples of sensors proposed around SERS technology 31034 PMT, and Ortec photon-counting electronics. Ei- are organochloride pesticides,'j various hazardous aro- ther a Spectra-Physics 2016 or a 2025 Kr+laser provided matic compounds adsorbed to surface^,^ electrochemi- 531-nm light for resonant excitation of EBT. The laser cally adsorbed chloropyridines,8 and ~yridine.~~~We re- power was adjusted to provide 20 mW at the sample after port here a new approach to SERS sensors which utilizes passing through a 531-nm interference filter. The inci- a Raman indicator. In this case the indicator is Erio- dent angle of the laser light to the substrate was 45". A chrome Black T (EBT). EBT has been explored by Seitz backscattering geometry was used with the exciting light and co-workers as the basis for an energy transfer/flu- focused on the sample through a cylindrical lens to de- orescence quenching fiber-optic sensor.l0The advantage crease the power density. The sample was spun at 1800 of SERS-based sensors is that the information content rpm to eliminate laser-induced damage and to provide of vibrational spectra is much larger than electronic spec- an average of the surface spectrum. An F2 collection lens tra, and when SERS is combined with resonance en- was used to focus the Raman light on the monochromator hancement the sensitivity of SERRS (Surface-Enhanced slits. The slits were adjusted to provide a 5-cm-1 band- Resonance Raman Spectroscopy) equals that of fluores- pass. cence spectroscopy.2Furthermore, the difficult problem Group I1 metals and Cu2+samples were prepared for of measuring absolute intensities is solved since the in- analysis by applying 150 pL of an aqueous buffer solution dicator is its own internal standard and a subtraction of metal + EBT to the SERS substrate. The EBT con- - centration was varied depending on the experiment. A technique using Icomplexed indicator Iuncomplexed indicator can be used. second procedure was tested for Pb2+ samples. In this case the EBT/metal complex was extracted with l-pen- tanol (Aldrich), the pentanol was evaporated, and the Received 28 September 1990. residue was redissolved in methanol. Fifty of the * Author to whom correspondence should be sent. pL t Current address: Royal Institute of Technology, S-100-44 Stockholm, methanol solution was applied to the SERS substrate. Sweden. In all cases the analyte solution was applied by spin 420 Volume 45, Number 3, 1991 OOO3-7028/91/4503-0420$2.00/0 APPLIED SPECTROSCOPY 0 1991 Society for Applied Spectroscopy 1380 .-./--. Mg I Ca W 1360 I I+ k 3: z 1340 63 d 1320 Sr I Ba i 1300 111111111 50 70 90 110 130 IONIC RADIUS (pm) FIG. 2. A plot of the frequency of the metal-dependent SERRS band and ionic radius. The ionic radii were taken from Ref. 13. be seen that in the low-wavenumber region several weak unique bands appear in the metal complex. The most significant differences are the loss of the 1274-cm-l band and the appearance of a metal-dependent band between 1364 and 1310 cm-l. The shift of the metal-dependent band can be correlated with the ionic radius. Figure 2 shows a plot of splitting vs. ionic radii for the alkaline I' I earths. The ionic radii were taken from Ref. 14, and a coordination number of 6 was assumed. The selectivity 1800 cin -1 200 advantage for SERS indicators over absorption spec- troscopy can be seen in Table I. We defined the resolving FIG.1. The difference spectra of EBT/alkaline earth SERRS spectra power as minus the SERRS spectrum of EBT. The spectra were taken with 20 mW of 531-nm laser excitation. The subtraction was from a blank taken = (peak separation)/FWHM. (1) under the same conditions as the EBT/metal complex spectra. The R 1274-cm-l band disappears in the complex, and a strong metal-depen- With respect to the Rayleigh criterion for resolution this dent 1364-1310 cm-l band appears. means that bands with R > 1will be resolved. It can be seen that for Mg2+versus Ca2+,Sr2+, and Ba2+none of coating to provide an even coverage. A slight vacuum was the EBT/metal absorption spectra would be resolved. maintained during the coating procedure to facilitate On the other hand, with SEERS all spectra except Mg2+/ solvent evaporation. EBT-Ca2+EBTcan be resolved. The EBT coverage was determined by absorbance Our first quantitative test of SERRS indicators was spectroscopy of solutions containing dissolved EBT rinsed the detection of Pb2+.Pb was chosen since it represents from 10 SERS substrates. The dissolution of EBT was an environmental hazard. Figure 3 shows the SERRS carried out with a pH 9 buffer solution. We determined spectrum of the EBT/Pb2+ complex. It was found that a molar absorptivity of 18,300 at 542 nm. This is in rea- the most significant change upon chelation was the dis- sonable agreement with literature values for an equilib- appearance of the 1274-cm-1 band, and the 1325-cm-1 rium of HL2- and L3-.12 Our coating procedure was found band gave the best results for Pb2+concentration mea- to produce an average coverage of 2 x 1014 molecules/ surements. Figure 4 shows a plot of the 1274-cm-l band cm2with a 1.8 x M EBT aqueous solution. TABLE I. Comparison of SERRS and absorption spectroscopy. RESULTS AND DISCUSSION Resolving power Figure 1 illustrates the qualitative aspects of SERRS Absorption detection of metals. We chose to use the alkaline earth Metals SERRSB spectroscopyb metals as a test case since they possess very similar chem- Ca-Mg 0.40 0.01 ical properties. The spectra in Fig. 1 are subtractions of Sr-Mg 3.22 0.22 EBT/metal minus EBT on rough silver substrates. The Ba-Mg 3.57 0.30 strongest bands in the SERRS spectrum of EBT are the a FWHMsERR, = 15 cm-l. stretches associated with the diazo nitrogens.13It can also FWHM,,, = 180 nm. APPLIED SPECTROSCOPY 421 4 5 6 7 PPb FIG.4. The SERRS concentration profile for Pb2+.The detection limit is 270 ppb as determined by the point at which the S/N = 3. Data below the detection limit were not used in the linear regression. The error bars represent the relative error.
Load more

Recommended publications
  • Sensitive Determination of PAH-DNA Adducts
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Matrix Design for Matrix-Assisted Laser Desorption Ionization: Sensitive Determination of PAH-DNA Adducts M. George, J. M. Y. Wellemans, R. L. Cerny, and M. L. Gross* Midwest Center for Mass Spectrometry, Department of Chemistry, University of Nebraska-Lincoln, Lincoln, Nebraska USA K. Li and E. L. Cavalieri Eppley institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, 600 South 42nd Street, Omaha, Nebraska USA Two matrices, 4-phenyl-cw-cyanocinnamic acid (ICC) and 4-benzyloxy-cu-cyanocinnamic acid (BCC), were identified for the determination of polycyclic aromatic hydrocarbon @‘AH) adducts of DNA bases by matrix-assisted laser desorption ionization. These matrices were designed based on the concept that the matrix and the analyte should have structural similarities. PCC is a good matrix for the desorption of not only PA&modified DNA bases, but also PAHs themselves and their rnetabolites. Detections can be made at the femtomolar level. (1 Am Sot Mass Spectrum 1994, 5, 1021-1025) he success of matrix-assisted laser desorption quire sensitive detection methods at the low picomole ionization (MALDI) for the sensitive detection of and mid-femtomole level, respectively [6]. T an analyte depends on the nature of the matrix. One method for detection that also gives structural Rational design of a matrix requires understanding of information is fast-atom bombardment (FAB) coupled the mechanism of MALDI. The mechanism is not fully with tandem mass spectrometry [6-81. Unfortunately, understood. Nevertheless, empirical criteria for matrix the combination lacks sensitivity because there is in selection have been suggested 111.
    [Show full text]
  • Isoprene Photochemistry Over the Amazon Rainforest
    Isoprene photochemistry over the Amazon rainforest Yingjun Liua, Joel Britob, Matthew R. Dorrisc, Jean C. Rivera-Riosc,d, Roger Secoe, Kelvin H. Batesf, Paulo Artaxob, Sergio Duvoisin Jr.g, Frank N. Keutscha,c,d, Saewung Kime, Allen H. Goldsteinh, Alex B. Guenthere,i, Antonio O. Manzij, Rodrigo A. F. Souzak, Stephen R. Springstonl, Thomas B. Watsonl, Karena A. McKinneya,1, and Scot T. Martina,m,1 aJohn A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138; bDepartment of Applied Physics, University of São Paulo, São Paulo 05508, Brazil; cDepartment of Chemistry, University of Wisconsin-Madison, Madison, WI 53706; dDepartment of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138; eDepartment of Earth System Science, University of California, Irvine, CA 92697; fDivision of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125; gDepartment of Chemistry, Universidade do Estado do Amazonas, Manaus, AM 69050, Brazil; hDepartment of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720; iPacific Northwest National Laboratory, Richland, WA 99354; jInstituto Nacional de Pesquisas da Amazonia, Manaus, AM 69067, Brazil; kDepartment of Meteorology, Universidade do Estado do Amazonas, Manaus, AM 69050, Brazil; lDepartment of Environmental and Climate Sciences, Brookhaven National Laboratory, Upton, NY 11973; and mDepartment of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138 Edited by Mark H. Thiemens, University of California, San Diego, La Jolla, CA, and approved April 13, 2016 (received for review December 23, 2015) Isoprene photooxidation is a major driver of atmospheric chemistry forests like Amazonia where there are few anthropogenic NO over forested regions.
    [Show full text]
  • Single-Molecule Fluorescence Detection
    Proc. Nadl. Acad. Sci. USA Vol. 86, pp. 4087-4091, June 1989 Biophysics Single-molecule fluorescence detection: Autocorrelation criterion and experimental realization with phycoerythrin (laser-induced fluorescence/femtomolar sensitivity/fluorescence assays/phycoerythrin oligomers) KONAN PECK*, LUBERT STRYERt, ALEXANDER N. GLAZERt, AND RICHARD A. MATHIES* *Department of Chemistry, University of California, Berkeley, CA 94720; tDepartment of Cell Biology, Stanford University School of Medicine, Stanford, CA 94305; and tDepartment of Microbiology and Immunology, University of California, Berkeley, CA 94720 Contributed by Lubert Stryer, February 10, 1989 ABSTRACT A theory for single-molecule fluorescence ofindividual molecules. In this paper, we present a theory for detection is developed and then used to analyze data from single-molecule fluorescence detection and apply it in de- subpicomolar solutions of B-phycoerythrin (PE). The distri- tecting phycoerythrin at concentrations as low as 1 fM. bution of detected counts is the convolution of a Poissonian continuous background with bursts arising from the passage of individual fluorophores through the focused laser beam. The THEORY autocorrelation function reveals single-molecule events and Consider a solution of fluorophores flowing through a fo- provides a criterion for optimizing experimental parameters. cused laser beam. The emission from the illuminated volume The transit time of fluorescent molecules through the 120-fl consists of bursts of fluorescence from molecules passing imaged volume was 800 ps. The optimal laser power (32 mW through the beam superimposed on a continuous background at 514.5 nm) gave an incident intensity of 1.8 x 1023 due to Rayleigh and Raman scattering from the solvent (Fig. photons-cm 2.S-, corresponding to a mean time of 1.1 ns lA).
    [Show full text]
  • I Fluorescent Detection of Chiral Amino Acids
    i Fluorescent Detection of Chiral Amino Acids: A Micelle Approach Gengyu Du Yilong, Sichuan, China B.S. in Chemistry University of Science and Technology of China, Hefei, China, 2015 A Dissertation presented to the Graduate Faculty of the University of Virginia in Candidacy for the Degree of Doctor of Philosophy Department of Chemistry University of Virginia April 2020 ii Abstract Fluorescent Detection of Chiral Amino Acids: A Micelle Approach 1,1’-Bi-2-naphthol (BINOL)-based fluorescent probes have been developed as powerful tools for the molecular recognition of many chiral molecules. High sensitivity and enantioselectivity for chiral amino acids have been achieved in organic media, but the recognition in water media has been limited by their poor solubility in aqueous solution. By using a diblock copolymer PEG-PLLA, 3,3’-diformyl-BINOL was encapsulated into micelles to form a micelle probe. It allowed the detection of chiral lysine (Lys) both chemoselectively and enantioselectively in carbonate buffer solution. A limit of detection (LOD) of 848 nM and 2nd order fit of ee detection was obtained for D-Lys. The chemoselectivity was attributed to the selective reaction of Lys’s terminal amino groups with the probe. Series of monoformyl-BINOL with varying substituents were synthesized and engineered into micelle probes. These probes achieved specific detection of chiral tryptophan (Trp) both enantioselectively and chemoselectively in carbonate buffer solution, with LOD of 2.6 µM and 1st order fit of ee detection. A non-C2 symmetric molecule, 3,3’-diformyl-tetrahydro-BINOL, was fabricated into a micelle probe. It achieved specific detection of chiral His both enantioselectively and chemoselectively in carbonate buffer solution, with LOD of 107 nM and 2nd order fit of ee detection.
    [Show full text]
  • 18.4.3.7 Detection and Quantification Capabilities
    18.4.3.7 Detection and quantification capabilities Among the most important Performance Characteristics of the Chemical Measurement Process (CMP) are those that can serve as measures of the underlying detection and quantification capabilities. These are essential for applications in research, international commerce, health, and safety. Such measures are important for planning measurements, and for selecting or developing CMPs that can meet specified needs, such as the detection or quantification of a dangerous or regulated level of a toxic substance. Equations 18.4.1-6 provide the basis for our considering the meaning of minimum detectable and minimum quantifiable amounts (signals, concentrations) in Analytical Chemistry. In each case, the determining factor is the distribution function of the estimated quantity (estimated net signal Sˆ , concentration or amount xˆ ). If normality can be assumed, it is sufficient to know the standard deviation of the estimated quantity as a function of S (or x). Detection limits (minimum detectable amounts) are based on the theory of hypothesis testing and the probabilities of false positives α, and false negatives ß. Quantification limits are defined in terms of a specified value for the relative standard deviation. It is important to emphasize that both types of limits are CMP Performance Characteristics, associated with underlying true values of the quantity of interest; they are not associated with any particular outcome or result. The detection decision, on the other hand, is result-specific; it is made by comparing the experimental result with the Critical Value, which is the minimum significant estimated value of the quantity of interest. Terminology. Unfortunately, a host of terms have been used within the chemical community to describe detection and quantification capabilities.
    [Show full text]
  • Towards the 1000 Atom Detection Limit for 244Pu. R
    50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132) 2978.pdf TOWARDS THE 1000 ATOM DETECTION LIMIT FOR 244PU. R. Trappitsch,1 M. R. Savina,1 J. M. Rolison,1 L. N. Harrison,1 and N. Dauphas2, 1Lawrence Livermore National Laboratory, Nuclear and Chemical Sciences Divi- sion, Livermore, CA 94551, ([email protected]) 2The University of Chicago, Enrico Fermi Institute, and Chicago Center for Cosmochemistry, Chicago, IL 60637 Introduction Plutonium-244 is a radionuclide with a size of ∼ 3% of the sample area we slowly desorbed half-life of 80 Ma that can only be produced by the rapid sample material from the surface, subsequently ionized neutron capture (r-) process. While the sources of the Pu neutrals using a three-color, three-photon resonance r-process are poorly constrained and heavily discussed ionization scheme, and then analyzed these photoions in [e.g.,1], optical spectroscopy of the neutron star merger a time-of-flight mass spectrometer. By assuming a ho- associated with the gravitational-wave event GW170817 mogeneous distribution of the sample material over the indicated the presence of freshly nucleosynthesized lan- surface we calculated that 2:6 × 105 239Pu, 3:7 × 104 thanides [2], a main product expected from r-process 240Pu, and 1:8 × 103 242Pu atoms were in the anal- nucleosynthesis calculations. Proxy measurements of ysis spot. Plutonium-238 and 241Pu atoms were also 244Pu in the early Solar System, measured via 244Pu in the analysis spot, however, interferences with non- fission-produced xenon in meteorites [3], show a rather resonantly ionized 238U and 241Am, respectively, pre- high abundance.
    [Show full text]
  • Limit of Detection for Calibration Methods
    Limit of detection for calibration methods MARÍA JOSÉ RODRÍGUEZ CUESTA Doctoral Thesis ROVIRA I VIRGILI UNIVERSITY Tarragona 2006 UNIVERSITAT ROVIRA I VIRGILI LIMIT OF DETECTION FOR SECOND-ORDER CALIBRATION METHODS. M. José Rodríguez Cuesta ISBN: 978-84-690-7787-0 / DL: T.1349-2007 UNIVERSITAT ROVIRA I VIRGILI LIMIT OF DETECTION FOR SECOND-ORDER CALIBRATION METHODS. M. José Rodríguez Cuesta ISBN: 978-84-690-7787-0 / DL: T.1349-2007 Limit of detection for second-order calibration methods Doctoral thesis ROVIRA I VIRGILI UNIVERSITY UNIVERSITAT ROVIRA I VIRGILI LIMIT OF DETECTION FOR SECOND-ORDER CALIBRATION METHODS. M. José Rodríguez Cuesta ISBN: 978-84-690-7787-0 / DL: T.1349-2007 UNIVERSITAT ROVIRA I VIRGILI LIMIT OF DETECTION FOR SECOND-ORDER CALIBRATION METHODS. M. José Rodríguez Cuesta ISBN: 978-84-690-7787-0 / DL: T.1349-2007 Rovira i Virgili University Department of Analytical Chemistry and Organic Chemistry Limit of detection for second-order calibration methods Dissertation presented by María José Rodríguez Cuesta to receive the degree Doctor of the Rovira i Virgili University European PhD Tarragona, 2006 Supervisor Dr. Ricard Boqué i Martí UNIVERSITAT ROVIRA I VIRGILI LIMIT OF DETECTION FOR SECOND-ORDER CALIBRATION METHODS. M. José Rodríguez Cuesta ISBN: 978-84-690-7787-0 / DL: T.1349-2007 UNIVERSITAT ROVIRA I VIRGILI LIMIT OF DETECTION FOR SECOND-ORDER CALIBRATION METHODS. M. José Rodríguez Cuesta ISBN: 978-84-690-7787-0 / DL: T.1349-2007 ROVIRA I VIRGILI UNIVERSITY Department of Analytical Chemistry and Organic Chemistry Dr
    [Show full text]
  • Chiral Separation of Amines by Non-Aqueous Capillary Electrophoresis Using Low Molecular Weight Selectors
    Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy 31 Chiral Separation of Amines by Non-Aqueous Capillary Electrophoresis using Low Molecular Weight Selectors YLVA HEDELAND ACTA UNIVERSITATIS UPSALIENSIS ISSN 1651-6192 UPPSALA ISBN 91-554-6524-2 2006 urn:nbn:se:uu:diva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
    [Show full text]
  • One-Step Hydrothermal Synthesis of Thioglycolic Acid Capped Cds
    www.nature.com/scientificreports OPEN One-step hydrothermal synthesis of thioglycolic acid capped CdS quantum dots as fuorescence Received: 1 March 2018 Accepted: 24 May 2018 determination of cobalt ion Published: xx xx xxxx Zhezhe Wang1,2, Xinxin Xing1,2, Yue Yang1,2, Rongjun Zhao1,2, Tong Zou3, Zidong Wang3 & Yude Wang2,3 Highly luminescent CdS quantum dots capped with thioglycolic acid (TGA@CdS QDs) were synthesized from cadmium chloride and thiourea as cadmium and sulfur sources via simple hydrothermal method. The room temperature photoluminescence (RTPL) properties of TGA@CdS QDs were investigated. The results indicate that the polarity of the solvent and the surface trap state resulted in the broadness Stokes shift between the maximum absorption wavelength and the emission wavelength of TGA@ CdS QDs. The Co2+ sensing properties of fuorescence determination were investigated using TGA@ CdS QDs. The as-synthesized CdS QDs exhibits the excellent selectivity and sensitivity of fuorescence quenching for cobalt ion (Co2+). The limit of detection (LOD) is as low as 0.05 μM which is much lower than maximum limit of cobalt ions in drinking water. The linear response range of Co2+ was from 0.5 to 80 μM. The sensing system revealed the advantages of low detection limit, excellent selectivity, high sensitivity, convenience and low cost. The color change of CdS QDs shows potential applications in the detection of Co2+. Cobalt, as an important micronutrient, is an essential component of vitamin B12, and plays a vitally important role in humans and biological systems1–3. However, cobalt could be a toxic compound at high concentrations which could cause many diseases such as asthma, decreased cardiac output, cardiac enlargement, heart disease, lung disease, dermatitis and vasodilation4.
    [Show full text]
  • Voltammetric Techniques
    Chapter 37 Voltammetric Techniques Samuel P. Kounaves Tufts University Department of Chemistry Summary General Uses • Quantitative determination of organic and inorganic compounds in aqueous and nonaqueous solutions • Measurement of kinetic rates and constants • Determination adsorption processes on surfaces • Determination electron transfer and reaction mechanisms • Determination of thermodynamic properties of solvated species • Fundamental studies of oxidation and reduction processes in various media • Determination of complexation and coordination values Common Applications • Quantitative determination of pharmaceutical compounds • Determination of metal ion concentrations in water to sub–parts-per-billion levels • Determination of redox potentials • Detection of eluted analytes in high-performance liquid chromatography (HPLC) and flow in- jection analysis 709 710 Handbook of Instrumental Techniques for Analytical Chemistry • Determination of number of electrons in redox reactions • Kinetic studies of reactions Samples State Species of interest must be dissolved in an appropriate liquid solvent and capable of being reduced or oxidized within the potential range of the technique and electrode material. Amount The amounts needed to obtain appropriate concentrations vary greatly with the technique. For example, cyclic voltammetry generally requires analyte concentrations of 10–3 to 10–5 M, whereas anodic strip- ping voltammetry of metal ions gives good results with concentrations as low as 10–12 M. Volumes may also vary from about 20 mL to less than a microliter (with special microelectrode cells). Preparation The degree of preparation required depends on both the sample and the technique. For determination of Pb(II) and Cd(II) in seawater with a microelectrode and square-wave anodic stripping voltammetry (ASV), no preparation is required. In contrast, determination of epinepherine in blood plasma at a glassy carbon electrode with differential pulse voltammetry (DPV) requires that the sample first be pre- treated with several reagents, buffered, and separated.
    [Show full text]
  • Vacuum-Enhanced Optical Nonlinearities with Organic Molecular Photoswitches
    Vacuum-enhanced optical nonlinearities with organic molecular photoswitches Marina Litinskaya1, ∗ and Felipe Herrera2, 3, y 1Department of Physics & Astronomy and Department of Chemistry, University of British Columbia, Vancouver, Canada, V6T 1Z1 2Department of Physics, Universidad de Santiago de Chile, Av. Ecuador 3493, Santiago, Chile. 3Millenium Institute for Research in Optics MIRO, Chile. (Dated: April 6, 2018) We propose a cavity QED scheme to enable cross-phase modulation between two arbitrarily weak classical fields in the optical domain, using organic molecular photoswitches as a disordered intracavity nonlinear medium. We show that a long-lived vibrational Raman coherence between the cis and trans isomer states of the photoswitch can be exploited to establish the phenomenon of vacuum-induced transparency (VIT) in high-quality microcavities. We exploit this result to derive an expression for the cross-phase modulation signal and demonstrate that it is possible to surpass the detection limit imposed by absorption losses, even in the presence of strong natural energetic and orientational disorder in the medium. Possible applications of the scheme include the development of organic nanophotonic devices for all-optical switching with low photon numbers. Organic chromophores and semiconducting polymers ulation between the probe and signal fields can reach are known for having very large optical nonlinearities [1], values that are orders of magnitude larger than without with applications in lasing [2], frequency conversion [3], the cavity, exceeding the detection limit imposed by ab- nonlinear microscopy [4], and all-optical switching [5]. sorption losses. Replacing the control laser by a strongly However, the typical magnitude of the nonlinear suscep- coupled vacuum represents a clear advantage for organic tibility in organic materials is still orders of magnitude materials with low laser damage thresholds [2].
    [Show full text]
  • Analysis and Quantitation of Fructooligosaccharides Using Matrix-Assisted Laser Desorption/Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry
    Anal. Chem. 2008, 80, 159-165 Analysis and Quantitation of Fructooligosaccharides Using Matrix-Assisted Laser Desorption/Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Richard R. Seipert,² Mariana Barboza,² Milady R. NinÄ onuevo,² Riccardo G. LoCascio,³,§ David A. Mills,³ Samara L. Freeman,| J. Bruce German,| and Carlito B. Lebrilla*,²,⊥ Department of Chemistry, Department of Viticulture and Enology, Microbiology Graduate Group, Department of Food Science and Technology, and School of Medicine, University of California, Davis, One Shields Avenue, Davis, California 95616 Inulin is a class of fructooligosaccharide (FOS) derived fructooligosacharides (FOS) are plant-derived oligosaccharides from plants, which is often used as a natural food composed of linear fructans with â-(2-1) linkages.6,7 Inulin has ingredient. Inulin is currently used as an additive in baked been proposed to act as a beneficial dietary ingredient by acting goods, dairy products, infant formula, and dietary supple- as a growth-stimulating substrate for bacteria in the human ments as a result of its purported health-promoting intestine. The potential for such stimulation of bacterial growth properties. The growth of health-promoting lactobacilli to constitute a ªprebioticº effect implies that there is a net and bifidobacteria is supported by FOS, giving it the improvement in the health of the human host as a direct result of classification of a prebiotic; however, its ability to selectiv- this growth.8 However, the scientific basis for claims of
    [Show full text]