Showing papers in "Analytical Chemistry in 1985"

Electrospray interface for liquid chromatographs and mass spectrometers.

Abstract: L'effluent de chromatographie en phase liquide projete electrostatiquement dans un bain de gaz froid cree une dispersion de gouttelettes chargees qui s'evapore rapidement. Lorsque les gouttelettes deviennent plus petites, l'augmentation de la densite de charge superficielle et la baisse du rayon de courbure creent un champ suffisamment fort pour desorber les ions du solute. Une partie passe a travers un canal et forme un jet libre supersonique, puis passera dans l'analyseur de masse

Electrokinetic chromatography with micellar solution and open-tubular capillary

Abstract: Fundamental characteristics of a new type of chromatography with micellar solutions of ionic surfactants were examined. Electrokinetic phenomena in open-tubular capillaries move two phases, aqueous and micellar, with different velocities and micellar solubilization operates as the distribution process of solutes. Sodium dodecyl sulfate (SDS) solutions and a 0.05 mm i.d. x 650 mm fused silica tube were employed and high dc voltages up to 25 kV were applied. Linear relationships were observed between current and migration velocities of water, micelle, and any solute, but not between applied voltages and the velocities. This discrepancy can be reasonably interpreted in terms of the temperature rise of the solution in the tube resulting from Joule heating. Optimum resolutions can be obtained when the capacity factor is about 2, because retention times are limited between those of an insolubilized solute or water and a totally solubilized solute or micelle. Observed dependence of capacity factors on current can also be explained by the temperature rise. Thermodynamic parameters in micellar solubilization were presented. 22 references, 10 figures, 4 tables.

Influence of the wavelength in high-irradiance ultraviolet laser desorption mass spectrometry of organic molecules

Abstract: Influence de la longueur d'onde sur la desorption laser d'ions provenant de solides organiques sur l'exemple d'aminoacides et de dipeptides

Automated fluorimetric method for hydrogen peroxide in atmospheric precipitation

Abstract: An automated analytical technique for the determination of hydrogen peroxide (H/sub 2/O/sub 2/) in the liquid phase has been developed. The chemistry of this technique is based on the reaction of H/sub 2/O/sub 2/ with horseradish peroxidase and p-hydroxyphenylacetic acid (POPHA). The resulting reaction forms the fluorescent dimer of POPHA. By use of conventional fluorescence detection techniques a detection limit of 1.2 x 10/sup -8/ M (0.4 ppbm) H/sup 2/O/sup 2/ is obtained for a 1.5-mL aqueous sample. The coefficient of variation is 0.66% at 1.6 x 10/sup -6/ M (53 ppbm). The analytical chemical reaction responds stoichiometrically to both H/sup 2/O/sup 2/ and organic hydroperioxides. To discriminate H/sup 2/O/sup 2/ from organic hydroperioxides, a novel dual-channel chemical flow system has been devised to separately determine total hydroperioxides and organic hydroperioxides. The concentration of H/sup 2/O/sup 2/ is determined by the difference between these two measurements. The system has been tested extensively for potential interferences commonly found in environmental aqueous samples, and none has been observed. 17 references, 4 figures, 2 tables.

Electrocatalytic and analytical response of cobalt phthalocyanine containing carbon paste electrodes toward sulfhydryl compounds

Abstract: Les electrodes du titre catalysent l'electrooxydation de composes tel que la cysteine, l'homocysteine, la N-acetylcysteine et le glutathion. Ces electrodes utilisees comme electrodes sensibles pour la detection amperometrique qui suit une chromatographie en phase liquide permettent la detection de ces composes

Internal surface reversed-phase silica supports for liquid chromatography

Abstract: Internal surface reversed-phase (ISRP) supports synthesized from commercially available porous silica particles with a variety of nominal pore diameters and specific surface areas are characterized with regard to physical and chromatographic properties. Bonded phase coverage, pore size, capacity and efficiency measurements are made upon the various ISRP supports in order to evaluate the effect that the physical properties of silica have upon the chromatographic performance of ISRP packings. In addition, various models that describe the pore structure of silica supports are discussed.

Isotopic analyses based on the mass spectrum of carbon dioxide.

Abstract: Measurements of carbon and oxygen isotopic abundances are commonly based on the mass spectrum of carbon dioxide, but analysis of that spectrum is not trivial because three isotope ratios (/sup 17/O//sup 16/O, /sup 18/O//sup 16/O, and /sup 13/C//sup 12/C) must be determined from only two readily observable ion-current ratios (45/44 and 46/44). Here, approaches to the problem are reassessed in the light of new information regarding the distribution of oxygen isotopes in natural samples. It is shown that methods of calculation conventionally employed can lead to systematic errors in the computed abundance of /sup 13/C and that these errors may be related to incorrect assessment of the absolute abundance of /sup 17/O. Further, problems arising during the analysis of samples enriched by admixture of /sup 18/O-labeled materials are discussed, and it is shown (i) that serious inaccuracies arise in the computed abundance of /sup 17/O and /sup 13/C if methods of calculation conventionally employed in the analysis of natural materials are applied to material labeled with /sup 18/O but (ii) that computed fractional abundances of /sup 18/O are always within 0.4% of the correct result. Methods for exact calculation of two isotope ratios when the third is known are presentedmore » and discussed, and a more exact approach to the computation of all three isotope ratios in natural materials is given. 16 references, 2 figures, 2 tables.« less

Spectrophotometric multicomponent analysis applied to trace metal determinations

Abstract: Quantitative spectrometric analysis of mixture components is featured for systems with low spectral selectivity, namely, in the ultraviolet, visible, and infrared spectral range. Limitations imposed by data reduction schemes based on ordinary multiple regression are shown to be overcome by means of partial least-squares analysis in latent variables. The influences of variables such as noise, band separation band intensity ratios, number of wavelengths, number of components, number of calibration mixtures, time drift, or deviations from Beer's law on the analytical result has been evaluated under a wide range of conditions providing a basis to search for new systems applicable to spectrophotometric multicomponent analysis. The practical utility of the method is demonstrated for simultaneous analysis of copper, nickel, cobalt, iron, and palladium down to 2 X 10/sup -6/ M concentrations by use of their diethyldithiocarbamate chelate complexes with relative errors less than 6%. 26 references, 4 figures, 6 tables.

Vacuum heat-treatment for activation of glassy carbon electrodes

Abstract: Le traitement thermique d'une electrode de carbone vitreux, a 725°C sous vide pousse (<2.10 −6 Torr) permet d'obtenir une electrode active vis-a-vis de l'oxydoreduction du ferro-ferricyanure et pour l'oxydation d'acide ascorbique

Liquid chromatographic separation of enantiomers using a chiral beta cyclodextrin bonded stationary phase and conventional aqueous organic mobile phases

Abstract: Separation d'enantiomeres d'aminoacides, de barbiturate, de dioxolanne et de derives de l'acide phenylacetique. Influence de la composition de la phase mobile, de la temperature de la vitesse d'ecoulement sur la selectivite et la resolution

Multisample conversion of water to hydrogen by zinc for stable isotope determination

Abstract: Deux techniques de reduction de H 2 O en hydrogene sont utilisees, l'un utilisant des tubes scelles pour l'eau formee sous vide et l'autre utilisant des capillaires pour les echantillons d'eau en bouteille

Determination of alkylphenols and alkylphenol mono- and diethoxylates in environmental samples by high-performance liquid chromatography

Abstract: A routine method is described for the quantitative determination of 4-nonylphenol (NP) and 4-nonylphenol mono-(NP1EO) and diethoxylate (NP2EO) in samples from wastewater and sludge treatment and from the aquatic environment. An exhaustive steam-distillation/solvent-extraction procedure was employed to enrich the analytes from aqueous and solid samples. Quantitative determinations were performed by normal-phase high-performance liquid chromatography (HP-LC) using aminosilica columns. Relative standard deviations were 3.0-4.4% in a river water containing 3.9 ..mu..g/L NP, 23.4 ..mu..g/L NP1EO, and 9.4 ..mu..g/L NP2EO. A digested sewage sludge with 1.6 g of NP/kg of dry matter was analyzed with a relative standard deviation of 3.7%. Recoveries were higher than 80%, and the estimated detection limit in water samples was 0.5 ..mu..g/L. Reversed-phase HPLC on octylsilica provided complementary qualitative data, particularly on homologous alkylphenolic compounds. Good agreement was found between quantitative determinations by HPLC and by high-resolution gas chromatography with flame ionization detection and directly coupled mass spectrometry. Municipal wastewater effluents, sewage sludges, and natural waters were analyzed to demonstrate the method's broad applicability. 19 references, 4 tables, 4 figures.

Qualitative near-infrared reflectance analysis using Mahalanobis distances

Abstract: Traitement des donnees par analyse discriminante; avantage d'utiliser les distances de Mahalanobis

Cyclic voltammetry and anodic stripping voltammetry with mercury ultramicroelectrodes

Abstract: A method for the preparation of mercury microvoltammetric electrodes of hemispherical geometry with radii of 2.3-7.3 ..mu..m has been developed. Mercury is electrodeposited from solutions of Hg(I) onto a microvoltammetric platinum disk electrode at a constant potential sufficient to ensure diffusion limited conditions. The radius of the deposited mercury electrode is a function of the square root of the deposition time and was experimentally evaluated by applying the equation for steady-state limiting current at a hemispherical electrode to the reduction of Ru(NH/sub 3/)/sub 6//sup 3 +/ at the mercury electrode. The mercury microvoltammetric electrode has been employed in several unique applications. Anodic stripping voltammetry with these electrodes can be performed with a quiescent solution during deposition due to the enhanced mass transfer resulting from nonlinear diffusion. The stripping peaks are as narrow as those expected for thin films, and the peak current for the stripping of lead was found to be linear over the concentration range of 7 x 10/sup -10/ M to 1 x 10/sup -7/ M (5-min preconcentration interval) and to have higher precision than conventional stripping techniques. Mercury microvoltammetric electrodes also are demonstrated to be of value in fast scan cyclic voltammetry in aqueous solution. A well-definedmore » wave can be obtained for the oxidized form of ascorbic acid at pH 7.0 at a scan rate greater than 1 kV s/sup -1/. 26 references, 3 figures, 2 tables.« less

Determination of trace metals in seawater by inductively coupled plasma mass spectrometry with preconcentration on silica-immobilized 8-hydroxyquinoline

Abstract: The application of inductively coupled plasma mass spectrometry (ICP-MS) to the determination of eight trace metals in a coastal seawater reference material is described. Accurate calibration has been achieved for Mn, Co, Ni, Cu, Zn, Cd, and Pb by standard additions techniques, while stable isotopes dilution has been applied for Cr, Ni, Cu, Zn, Cd, and Pb. In both cases the race metals were separated from the seawater and concentrated 50-fold by adsorption on silica-immobilized 8-hydroxyquinoline prior to instrumental determination. Detection limits are in the range from 0.2 to 2 ng L/sup -1/, low enough to permit the analysis of even open ocean samples. 12 references, 4 figures, 3 tables.

Electroanalysis with chemically modified electrodes

Abstract: Modification des electrodes par depots de films de copolymeres (polyvinylpyridine/vinylferrocene et polyvinylbipyridine/vinylferrocene) qui comprennent un centre electroactif et un site de coordination, ce qui permet des electroanalyses d'ions metalliques avec une bonne sensibilite et selectivite

Synthesis and properties of high-temperature mesomorphic polysiloxane (MEPSIL) solvents: biphenyl- and terphenyl-based nematic systems

Abstract: Synthese, caracterisation de polysiloxanes utilisables comme phase stationnaire en chromatographie en phase gazeuse

Separation of metallocene enantiomers by liquid chromatography: chiral recognition via cyclodextrin bonded phases

Abstract: The LC separation of 13 enantiomeric pairs of ferrocene, ruthenocene, and osmocene analogues is described. Recently developed ..beta..-cyclodextrin bonded columns, which contain no interfering nitrogen or sulfur linkages, are particularly well suited to the separation of these compounds. The effect of solute structure and size on resolution and separation efficiency is examined. Both the application of this system and the mechanism of separation are discussed. 33 references, 3 figures, 1 table.

Nitrite-selective liquid membrane electrode

Abstract: Description d'une electrode a membrane liquide a base d'un derive lipophyle de la vitamine B 12 qui a une selectivite pour NO 2 − >SCN − >ClO 4 − >Cl − ∼NO 3 −

Filar electrodes: steady-state currents and spectroelectrochemistry at twin interdigitated electrodes

Abstract: Description d'une methode permettant de produire des courants stationnaires entre 2 electrodes coplanaires, tres proches l'une de l'autre, et de mesurer simultanement l'absorbance des especes electroactives

Three-component curve resolution in liquid chromatography with multiwavelength diode array detection

Abstract: Theorie du calcul pour trois composes eleves. Etude experimentale utilisant des routines de calcul sur des equipements Hewlett-Packard

Liquid Chromatographic Separation of Diastereomers and Structural Isomers on Cyclodextrin-Bonded Phases

Abstract: On separe des isomeres de structure (hydrocarbures aromatiques polycycliques et prostaglandines), des isomeres geometriques des steroides epimeres sur colonnes a liaison cyclodextrine. Il y a formation de complexes d'inclusion

Thin-layer electrochemical detector with a glassy carbon electrode coated with a base-hydrolyzed cellulosic film.

Abstract: Permeabilite et applications analytiques d'un detecteur electrochimique en carbone vitreux couche mince protege par un film de cellulose, ces electrodes sont utilisees en chromatographie liquide et analyse par injection dans un flux. La protection permet une meilleure stabilite et selectivite de l'electrode