Showing papers in "Analytical Chemistry in 1989"

Scanning electrochemical microscopy. Introduction and principles

Abstract: The technlque of scannlng electrochemical mlcroscopy (SECM) Is descrlbed. In thls technlque the electrolysls current that flows as an ultramicroelectrode tlp (diameter ca. 10 gm) Immersed In a soiutlon Is moved above a substrate surface is used to characterize processes and structural features of the substrate. Modes of Operation consldered Include collectlon modes, where products electrogenerated at the substrate are detected at the tip (held at constant potentlal or operated In the cyclic voltammetrlc mode), and feedback modes, where the effect of substrate on the tlp current Is monltored. The feedback mode can be used with both conductive and lnsulatlng substrates and Is less sensithe to electrlcal coupllng between substrate and tlp. An ailernatlng current generatlon/collectlon mode Is also described. Experimental results for the different modes of Operation and proposed extensions of the SECM technlque are presented.

Nanogram nitrite and nitrate determination in environmental and biological materials by vanadium (III) reduction with chemiluminescence detection.

Abstract: Nitrite in environmental water samples is reduced at room temperature to nitric oxide in acidic medium containing vanadium (III). Nitrate is also rapidly reduced after heating to 80-90 degrees C. Nitric oxide is removed from the reaction solution by scrubbing with helium carrier gas and is detected by means of a chemiluminescence NOx analyzer. Nanogram detection limits are obtained. The method has the advantage of not requiring highly acidic solutions for nitrate reduction and has been applied to the analysis of a variety of environmental waters, sediment, plant materials, and human urine and blood serum.

Scanning electrochemical microscopy. Theory of the feedback mode

Abstract: The steady-state current that flows between the scanning tlp (a disk ultramicroelectrode imbedded in an Insulating sheath) and a planar sample substrate in a scannlng electrochemical microscope (SECM) operating in the feedback mode is calculated by the finite element method with an exponentlaily expandlng grld, for both conductlve and Insulating samples. For conductlve substrates the tip current, representing, for example, the oxidatkn reactlon of R to 0, is enhanced by flow of R generated at the substrate to the tlp and is a functlon of tiphubstrate distance, d, but not the radius of the lnsuiatlng sheath. For insulating substrates, the tlp current Is decreased by blockage of the diffusion of R to the tip by the substrate and depends upon d and the Insulating sheath radius. The theoretical results are compared to experimental studies.

Thermodynamic study on the effects of beta-cyclodextrin inclusion with anilinonaphthalenesulfonates.

Abstract: Thermodynamic parameters and stoichiometries for the binding of anilinonaphthalenesulfonates to beta-cyclodextrin are obtained from steady-state fluorescence intensity and anisotropy measurements. Specifically, formation constant, enthalpy, and entropy values are obtained for complexes of beta-cyclodextrin with eight different substrate molecules at five different temperatures and six different pH values, and their associated errors are given. We propose an explanation of the relative magnitudes of the values obtained with regard to the geometry of the substrate and the importance of the various noncovalent interactions responsible for the complexation.

Quantitative determination of low molecular weight carboxylic acids by capillary zone electrophoresis/conductivity detection

Abstract: Low molecular weight carboxylic acids are separated and quantitated by capillary zone electrophoresis (CZE) with an on-column conductivity detector. The addition of 0.2-0.5 mM TTAB (tetradecyltrimethylammonium bromide) controls the electroosmotic flow so that all carboxylate anions pass through the detector. Unlike other CZE detection methods, conductivity detection shows a direct relationship between retention time and peak area. This confers on conductivity detection, in CZE, the unique advantage that use of an internal standard allows accurate determination of absolute concentrations in a mixture without separate calibration of response for each component.

Preparation and evaluation of packed capillary liquid chromatography columns with inner diameters from 20 to 50 μm

Abstract: Etude de l'effet du diametre de la colonne sur la performance de la colonne garnie de silice fondue modifiee par le groupement octyl

Application of free-solution capillary electrophoresis to the analytical scale separation of proteins and peptides.

Abstract: The application of free solution capillary electrophoresis (FSCE) to the separation of protein and peptide mixtures is presented. Both qualitative and quantitative aspects of FSCE separations are considered. In addition, a brief introduction describing the separation principle behind FSCE separations and a discussion of electrophoretic mobility are included. The applications were chosen in order to highlight the selectivity of FSCE separations and to demonstrate applications of potential practical interest to the bioanalytical chemist. Comparison of FSCE relative to traditional analytical separation alternatives is stressed throughout. The examples are presented in three broad categories: protein separations, peptide separations, and the application of both to the analysis of recombinant protein products. In the first section, FSCE separations of peptide mixtures are presented which demonstrate the suitability of FSCE for the analysis of the purity of peptide samples, the homogeneity of peptide samples prior to sequencing, the identity of peptides by using electrophoretic mobility values, and the reduction of an intrachain disulfide bridge. In the second section, protein separations are presented that show the resolution of glycoproteins having the same primary structure and the separation of immune complexes from free unreacted antibody and antigen. In the final section, highly purified and well-characterized samples of biosynthetic human insulin (BHI), biosynthetic human growth hormone (hGH), and their derivatives were used to evaluate FSCE as a complement and/or alternative to conventional analytical separation techniques for the determination of purity and identity of biosynthetic human proteins. In addition, the quantitative aspects of FSCE analysis such as linearity of response, precision, and limit of detection were examined.

Synthesis and characterization of highly stable bonded phases for high-performance liquid chromatography column packings

Abstract: Synthese d'une silice modifiee par des silanes et presentant une bonne stabilite a l'hydrolyse

Effect of temperature gradients on the efficiency of capillary zone electrophoresis separations

Abstract: Influence de la chaleur generee dans les tubes sur l'efficacite du systeme electrophoretique. Il semblerait que seul les profils paraboliques de temperatures decrivent les gradients de temperatures de maniere correcte. Optimisation des conditions operatoires pour minimiser les effets indesirables des gradients thermiques

Prediction of gasoline octane numbers from near-infrared spectral features in the range 660-1215 nm

Abstract: The feasibility of predicting the quality parameters of gasoline from its absorption spectrum in the wavelength range 660-1215 nm was investigated. In this spectral region, vibrational overtones and combination bands of CH groups of methyl, methylene, aromatic, and olefinic functions were observed. With the aid of multivariate statistics, the spectral features could be correlated to various quality parameters of gasoline such as octane number. As an example, multivariate analysis of the spectra of 43 unleaded gasoline samples yielded a three-wavelength prediction equation for pump octane that gave excellent correlations (R/sup 2/ = 0.95; standard error of estimate, 0.3-0.4 octane number; standard error of prediction, 0.4-0.5 octane number) with the ASTM motor determined octane numbers. Independent multivariate analysis using partial least-squares (PLS) regression yielded similar results. An additional set of nine samples from the Pacific Coast Exchange Group of the ASTM were examined for ten different quality parameters (research and motor octane numbers, Reid vapor pressure, API gravity, bromine number, lead, sulfur, aromatic, olefinic, and saturate contents). Regression analysis of the spectra results in correlation of nine of the ten properties with R/sup 2/ values ranging from 0.94 to 0.99 and standard errors near the independent reference test values.

An error analysis of the rapid lifetime determination method for the evaluation of single exponential decays

Abstract: The precision and speed of Ashworth's rapid lifetime determination method (RLD) for a single exponential decay is evaluated The RLD is compared to the weighted linear least-squares (WLLS) method Results are presented as a function of integration range and signal noise level For both the lifetime and the preexponential factor, optimum fitting regions exist, yet the errors increase rather slowly on either side of the optimum The optimum conditions for determination of the preexponential factor and the lifetime are similar, so both can be determined with good precision even at low total counts (10/sup 4/) In the optimum region, the relative standard deviations for the RLD are only 30-40% worse than for WLLS, but the calculations are tens to hundreds of times faster, depending on how the data are taken The speed and precision of the RLD coupled with the ease of data acquisition make it an attractive data reduction tool for real time analyses

Surface-Enhanced Raman Spectroscopy.

Abstract: Robin L. Garrell of the University of Pittsburgh reviews the basis of SERS and its experimental requirements, she also describes some examples of analytical problems to which SERS can be applied.

Band broadening in electrokinetic chromatography with micellar solutions and open-tubular capillaries

Abstract: Etude du phenomene d'elargissement de bandes lors de chromatographie electrocinetique. Passage en revue des differentes causes d'elargissement de bandes (diffusion longitudinale, cinetique de sorption-desorption, transfert de masse intermicellaire, influence du gradient de temperature radiale sur la vitesse electrophoretique, dispersion electrophoretique des micelles,…)

Enzyme monolayer- and bilayer-modified tin oxide electrodes for the determination of hydrogen peroxide and glucose

Abstract: An enzyme-based amperometric biosensor for hydrogen peroxide was developed, employing a horseradish peroxidase (HRP) monolayer covalently attached to a tin oxide electrode and a dissolved electron mediator. The sensor can determine hydrogen peroxide at levels down to 10{sup {minus}8} M and can be applied to a flow system. Stability of the electrode, kinetics of the surface process, and the efficiencies of different mediators were studied. As an extension, glucose oxidase (GOx) was chemically bound to the HRP-modified electrode. A GOx/HRP bilayer-modified electrode thus obtained exhibits much better performance in glucose detection limit, sensitivity, and response speed than previously reported GOx monolayer-modified electrodes.

Quantitative relationship between electron transfer rate and surface microstructure of laser-modified graphite electrodes

Abstract: Prevlous lnvestlgatlons demonstrate that Increases In electron transfer rate constant, ko, on hlghly ordered pyrolytic graphlte (HOPG) basal plane correlate wlth the appearance of edge plane defects and that such defects may be created wlth laser or electrochemlcal pretreatment. In the current work both capacltance (C Ob) and k Ob for Fe(CN),s'C on HOPG were measured as functions of power density of the actlvatlng laser. Over a power density range from 0 to 130 MW cm-2, ko* Increased by more than 5 orders of magnitude whlle Cow Increased by a factor of 8. Both kob and Cob may be expressed as linear comblnatlons of the basal and edge plane ko and Co values, welghted by the fractlonal coverage of edge plane on the electrode surface (t,). Determinations of f, from both k0* and C',,,,, are quantltatlvely conslstent and In both cases Increase wlth power density above a threshold of 45 MW cm-2. Although effects of surface roughness may also be Involved, the results Indicate that the electron transfer actlvlty of laser-modlfled HOPG Is predominantly dependent on edge plane denslty.

Global optimization by simulated annealing with wavelength selection for ultraviolet-visible spectrophotometry

Abstract: A new approach, leading to a fragmental property index family, FPIF, is presented. Indices are calculated as local descriptors of some molecular fragments and the global values are then obtained by summing the fragmental contributions. The modeling ability of FPIF is demonstrated by modeling some physico-chemical properties and biological activities on selected sets of organic compounds. The results are compared to those reported in some previous works. References Free, S.M., Wilson, J.W. A mathematical contribution to structure-activity studies (1964) J. Med. Chem., 7, p. 395. Gao, C., Govind, R., Tabak, H.H. Application of the group contribution method for predicting the toxicity of organic chemicals (1992) Environmental Toxicol. Chem., 11, pp. 631-636. Kalivas, J.H., Sutter, J.M., Roberts, N. Global optimization by simulated annealing with wavelength selection for ultraviolet-visible spectrophotometry (1989) Anal. Chem., 61, pp. 2024-2030. Kalivas, J.H. Generalized simulated annealing for calibration sample selection from an existing set and orthoginization of undesigned experiments (1991) J. Chemometrics, 5, pp. 37-48. Scopus Print Document1 Page 1 of 6 1/12/2007 http://www.scopus.com/scopus/citation/print.url?origin=recordpage&sid=&src=s&stateKey=OFD_5503704&eid=2-s2.... Sutters, J.M., Dixon, S.L., Jurs, P.C. Automated descriptor selection for Quantitative StructureActivity Relationships, using generalized simulated annealing (1995) J. Chem. Inf. Comput. Sci., 35, pp. 77-84. Leardi, R., Boggia, R., Terrile, M. Genetic algorithms as a strategy for feature selection (1992) J. Chemom., 6, p. 267. Lucasius, C.B., Kateman, G. Undersanding and using genetic algorithms. Part 1. Concepts, properties and context (1993) Chemom. Intell. Lab. Sys., 19, p. 1. Diudea, M.V. Cluj matrix CJu : Source of various graph descriptors (1997) Commun. Math. Comput. Chem. (MATCH), 35, pp. 169-183. Diudea, M.V., Minailiuc, O., Katona, G., Gutman, I. Szeged matrices and related numbers (1997) Commun. Math. Comput. Chem. (MATCH), 35, pp. 129-143. Diudea, M.V. Cluj matrix invariants (1997) J. Chem. Inf. Comput. Sci., 37, pp. 300-305. Diudea, M.V., Pârv, B., Topan, M.I. Derived Szeged and Cluj indices (1997) J. Serb. Chem. Soc., 62, pp. 267-276. Diudea, M.V., Gutman, I. Wiener-type tpological indices (1998) Croat. Chem. Acta, 71, pp. 21-51. Kiss, A.A., Katona, G., Diudea, M.V. Szeged and Cluj matrices within the matrix operator W (M1,M2,M3) (1997) Coll. Sci. Papers Fac. Sci. Kragujevac, 19, pp. 95-107. Gutman, I., Diudea, M.V. Defining Cluj matrices and Cluj matrix invariants (1998) J. Serb. Chem. Soc., 63, pp. 497-504. Diudea, M.V., Parv, B., Gutman, I. Detour-Cluj matrix and derived invariants (1997) J.Chem.Inf.Comput.Sci., 37, pp. 1101-1108. Scopus Print Document2 Page 2 of 6 1/12/2007 http://www.scopus.com/scopus/citation/print.url?origin=recordpage&sid=&src=s&stateKey=OFD_5503704&eid=2-s2.... Diudea, M.V., Katona, G., Lukovits, I., Trinajstić, I. Detour and Cluj-detour indices (1998) Croat. Chem. Acta, 71, pp. 459-471. Minailiuc, O., Katona, G., Diudea, M.V., Strunje, M., Graovac, A., Gutman, I. Szeged fragmental indices (1998) Croat. Chem. Acta, 71, pp. 473-488. Horn, R.A., Johnson, C.R. (1985) Matrix Analysis, Diudea, M.V., Gutman, I., Jäntschi, L. Molecular Topology, Sears, F.W., Zemansky, M.W., Young, H.D. (1976) University Physics, Fifth Edition, Addison Wesley Publishing Company, Golender, V., Vesterman, B., Vorpagel, E. APEX-3D Expert system for drug design (1996) Network Science, Rose, V.S., Wood, J. Generalized cluster significance analysis and stepwise cluster significance analysis with conditional probabilities (1998) Quant. Struct.-Act. Relat., 17, pp. 348-356. Young, H.D. (1962) Statistical Treatment of Experimental Data, Reif, F. (1965) Fundamentals of Statistical and Thermal Physics, Diudea, M.V., Silaghi-Dumitrescu, I. Valence group electronegativity as a vertex discriminator (1989) Rev. Roumaine Chim., 34, pp. 1175-1182. Diudea, M.V., Kacso, I.E., Topan, M.I. Molecular topology. 18. A Qspr/Qsar study by using new valence group carbon-related electronegativities (1996) Rev. Roum. Chim., 41, pp. 141-157. Crawford Jr., F.S. (1968) Waves, 3. Ivanciuc, O. 3D QSAR models Scopus Print Document3 Page 3 of 6 1/12/2007 http://www.scopus.com/scopus/citation/print.url?origin=recordpage&sid=&src=s&stateKey=OFD_5503704&eid=2-s2.... QSPR/QSAR Studies by Molecular Descriptors, Hopfield, J.J. Neural networks and physical systems with emergent collective computational abilities (1982) Proc. Natl. Acad. Sci. U.S.A., 79, pp. 2554-2558. Zupan, J., Gasteiger, J. Neural networks: A new method for solving chemical problems or just a passing phase? (1991) Anal. Chim. Acta, 248, pp. 1-30. Gasteiger, J., Zupan, J. Neural networks in chemistry (1993) Angew. Chem. Int. Ed. Engl., 32, pp. 503-527. Zupan, J., Gasteiger, J. (1993) Neural Networks for Chemists, Bulsari, A.B. (1995) Neural Networks for Chemical Engineers, Devillers, J. (1996) Neural Networks in QSAR and Drug Design, p. 279. Ivanciuc, O., Rabine, J.-P., Cabrol-Bass, D., Panaye, A., Doucet, J.P. 13C NMR chemical shift prediction of sp2 carbon atoms in acyclic alkenes using neural networks (1996) J. Chem. Inf. Comput. Sci., 36, pp. 644-653. Ivanciuc, O. Molecular graph descriptors used in neural network models (1999) Topological Indices and Related Descriptors in QSAR and QSPR, pp. 697-777. Gakh, A.A., Gakh, E.G., Sumpter, B.G., Noid, D.W. Neural network-graph theory approach to the prediction of the physical properties of organic compounds (1994) J. Chem. Inf. Comput. Sci., 34, pp. 832-839. Baskin, I.I., Palyulin, V.A., Zefirov, N.S. A Neural device for searching direct correlations between structures and properties of chemical compounds (1997) J. Chem. Inf. Comput. Sci., 37, pp. 715-721. Kireev, D.B. ChemNet: A Novel neural network based method for Scopus Print Document4 Page 4 of 6 1/12/2007 http://www.scopus.com/scopus/citation/print.url?origin=recordpage&sid=&src=s&stateKey=OFD_5503704&eid=2-s2.... graph/property mapping (1995) J. Chem. Inf. Comput. Sci., 35, pp. 175-180. Topliss, J.G., Edwards, R.P. Chance factors in in studies of Quantitative Structure-Activity Relationships (1979) J. Med. Chem., 22, p. 1238. Nikolić, S., Medić-Sarić, M., Matijević-Sosa, J. A QSAR study of 3-(Phtalimidoalkyl)-pyrazolin-5-ones (1993) Croat. Chem. Acta, 66, pp. 151-160. Nagy, P.I., Tokarski, J., Hopfinger, A.J. Molecular shape and QSAR analysis of a family of substituted dichlorodiphenyl aromatase inhibitors (1994) J. Chem. Inf. Comput. Chem., 34, pp. 1190-1197. Wessel, M.D., Jurs, P.C. Prediction of normal boiling points for a diverse set of industrially important organic compounds from molecular structure (1995) J. Chem. Inf. Comput. Sci., 35, pp. 841-850. Stanton, D.T., Jurs, P.C. Development and use of charged partial surface area structural descriptors for Quantitative Structure-Property Relationships studies (1990) Anal. Chem., 62, p. 2323. Goll, E.S., Jurs, P.C. Prediction of the Normal Boiling Points of Organic Compounds from Molecular Structures with a Computational Neural Network Model (1999) J. Chem. Inf. Comput. Chem., 39, pp. 974-983. Stuper, A.J., Brugger, W.E., Jurs, P.C. (1979) Computer-assisted Studies of Chemical Structure and Biological Function, Trebst, A., Draber, W. Advan. Pest. Sci (1978) Symp. Papers IV-th Int. Congress Pest. Chem., p. 223. Benigni, R., Gallo, G., Giorgi, F., Giuliani, A. On the equivalence between different descriptions of molecules: Value for computational approaches Scopus Print Document5 Page 5 of 6 1/12/2007 http://www.scopus.com/scopus/citation/print.url?origin=recordpage&sid=&src=s&stateKey=OFD_5503704&eid=2-s2.... Correspondence Address Diudea M.V.; Fac. of Chem. and Chem. Engineering; Babes-Bolyai University 3400 Cluj, Romania ISSN: 03406253 Language of Original Document: English Abbreviated Source Title: Match Copyright © 2007 Elsevier B.V. All rights reserved. Scopus ® is a registered trademark of Elsevier B.V. (1999) J. Chem. Inf. Comput. Sci., 39, pp. 575-578. Scopus Print Document6 Page 6 of 6 1/12/2007 http://www.scopus.com/scopus/citation/print.url?origin=recordpage&sid=&src=s&stateKey=OFD_5503704&eid=2-s2.... Modeling Molecular Properties by Cluj Indices Lorentz Jäntschi, Gabriel Katona and Mircea V. Diudea Faculty of Science and Engineering of Materials, Technical University Bios Research and Production Center Faculty of Chemistry and Chemical Engineering, “Babeş-Bolyai” University 3400 Cluj, Romania Abstract. A new approach, leading to a fragmental property index family, FPIF, is presented. Indices are calculated as local descriptors of some molecular fragments and the global values are then obtained by summing the fragmental contributions. The modeling ability of FPIF is demonstrated by modeling some physico-chemical properties and biological activities on selected sets of organic compounds. The results are compared to those reported in some previous works. A new approach, leading to a fragmental property index family, FPIF, is presented. Indices are calculated as local descriptors of some molecular fragments and the global values are then obtained by summing the fragmental contributions. The modeling ability of FPIF is demonstrated by modeling some physico-chemical properties and biological activities on selected sets of organic compounds. The results are compared to those reported in some previous works. Commun. Math. Comput. Chem. (MATCH), 2000, 41, 151-188 Introduction QSPRs (Quantitative Structure-Property Relationships) link quantitatively the physico-chemical properties of chemical compounds with the molecular structure. They provide mathematical models aimed to accurately predict a certain property from the structural attributes. Some molecular properties (i.e. those of which numerical value vary with changes in the molecular structure) such as the normal boiling point, critical parameters, viscosity, solubility, retention chr

Salicylate-selective membrane electrode based on tin(IV) tetraphenylporphyrin.

Abstract: The response properties of a new solvent/polymeric membrane electrode with unique selectivity toward anionic salicylate are reported. The electrode is prepared by incorporating 5, 10, 15, 20-tetraphenyl(porphyrinato)tin(IV) dichloride (Sn[TPP]Cl2) into a plasticized poly(vinyl chloride) membrane. The resulting sensor exhibits an anti-Hofmeister selectivity pattern, with high specificity for salicylate over lipophilic inorganic anions (perchlorate, periodate, thiocyanate, iodide, etc.) and biological organic anions (citrate, lactate, acetate). Moderate selectivity over structural analogues of salicylate (3- and 4-hydroxybenzoate, benzoate) is also observed. Radiotracer uptake experiments using [14C]salicylate clearly show that the metal center of the metalloporphyrin is critical for selective salicylate transport in the membrane phase. Minimal response to chloride ions makes the new electrode potentially useful for estimating salicylate levels in biological samples.

Multivariate determination of glucose in whole blood by attenuated total reflection infrared spectroscopy

Abstract: A spectral analysis of whole EDTA blood was undertaken by using attenuated total reflection and Fourier-transform infrared spectroscopy. The concentration of blood glucose was measured by an enzymatic method using glucose dehydrogenase and ranged between 40 and 290 mg/dL with an average concentration of 90.4 mg/dL. Multivariate calibration with the partial least-squares (PLS) algorithm was performed on spectral data between 1500 and 750 cm-1 showing a varying background from different unidentified interfering compounds. Cross validation was carried out for optimizing the PLS model. PRESS was 19.8 mg/dL, which was calculated on the basis of 127 standards, whereas the estimated standard deviation for the calibration fit was computed to be 11.9 mg/dL. Infrared spectroscopy can be used for monitoring glucose levels within the normal physiological range in a complex matrix like whole blood as an alternative to electrochemical sensors.

Scanning electrochemical microscopy. Apparatus and two-dimensional scans of conductive and insulating substrates

Abstract: The applicatlon of scannlng electrochemical microscopy (SECM) in the feedback mode to two-dknenslonai scans over conductlve and insuiatlng substrates to obtain topographic information at the micrometer-level Is descrlbed. In the feedback mode the effect of the conductlvlty of the substrate and dlstance of the substrate from a scanning ultramicroelectrode tlp on the current flowing at the tip caused by an electrode reaction Is recorded as a function of the tlp x-y position. Experiments wlth a 50-pm Pt wlre on glass, a ca. 50-pm glass fiber on glass, a gold mkrlgrkl, a Pt fdl, and a KCI crystal In both aqueous and acetonitrile solutions are presented. The construction of the SECM and the hardware and software that control three-dimensional tip movement and data acqulsltlon are also described.

Continuous liquid-phase piezoelectric biosensor for kinetic immunoassays.

Abstract: The reactions of immunoglobulins with protein A and, subsequently, of antibodies to these immunoglobulins were continuously monitored by a piezoelectric biosensor. AT-cut crystals, with a fundamental resonant frequency of 10 MHz, were mounted in a Plexiglas holder, and one side was directly coated with protein A. Upon exposure to solutions containing rabbit or human IgG the resonant frequency was followed continuously and its decrease due to the binding of IgG to protein A observed. Subsequent addition of sheep antihuman IgG to the now immobilized human IgG caused a specific 3-fold further decrease in resonant frequency. We observed a frequency change of approximately 1 Hz fore each 10 ng of added immunoglobulin. Decreasing the pH to 3 released the bound IgG but not the protein A and permitted reuse of the crystal for further IgG binding.

Dimethyl disulfide derivatives of long chain alkenes, alkadienes, and alkatrienes for gas chromatography/mass spectrometry

Abstract: La chromatographie capillaire en phase gazeuse couplee a la spectrometrie de masse par impact d'electron des adduits d'hydrocarbures et de dimethyldisulfure permet la localisation des doubles liaisons internes et terminales. La reaction dure au total quatre heures. Etude des isomeres

Constant potential amperometric detection of carbohydrates at a copper-based chemically modified electrode

Abstract: L'electrode utilisee dans ce systeme est constituee d'une electrode de carbone a l'etat vitreux recouverte d'une couche de cuivre(II) catalysant l'oxydation des oses en solution basique lorsqu'un courant positif capable de generer du cuivre(III) est applique Les oses suivant, glucose, D-ribose, fructose, sucrose, lactose, maltose, desoxy-2-D-ribose ont ete detectes par cette technique

Fluorometric measurement of aqueous ammonium ion in a flow injection system

Abstract: An automated flow-injection method for NH/sub 3//NH/sub 4//sup +/ involving the ternary reaction of the analyte with o-phthaldialdehyde (OPA) and sulfite is described. The use of malodorous thiol compounds is avoided and the reaction provides much greater sensitivity by either fluorescence (detection limit 300 fmol or 20 nM NH/sub 4//sup +/) or absorption detection compared to the reaction involving 2-mercaptoethanol. The reaction shows considerable selectivity for ammonia over amino acids by a factor of 16 to > 500 for 11 common amino acids studied. The throughput rate is 25 samples/h.

Determination of iron, cobalt, copper, zinc, rubidium, molybdenum, and cesium in human serum by inductively coupled plasma mass spectrometry.

Abstract: A method was developed for the determination of seven trace elements (Fe, Co, Cu, Zn, Rb, Mo, and Cs) in human serum by inductively coupled plasma mass spectrometry (ICP-MS). Sample preparation was kept as limited as possible. As the only sample pretreatment serum samples were diluted with nitric acid and indium was added as an internal standard. The results for iron, cobalt, copper, and zinc were corrected for interferences from polyatomic ions by using a blank solution containing the same concentration of sodium, sulfur, chlorine, and calcium as human serum. For copper and zinc the corrections are small, whereas for iron and cobalt they are important. No interferences occur for the considered isotopes of rubidium, molybdenum, and cesium. In order to test the accuracy and precision of the analytical technique, a "second-generation biological reference material (human serum)" was analyzed. The results obtained by ICP-MS for the seven elements considered showed good agreement with the certified values.

Electrochemical activation of carbon electrodes in base: minimization of dopamine adsorption and electrode capacitance

Abstract: Les conditions optimales pour l'activation electrochimique d'une electrode de carbone utilisee dans l'analyse sont determinees. L'adsorption de la dopamine sur ces electrodes est etudiee