Showing papers in "Analytical Chemistry in 1984"

Electrokinetic separations with micellar solutions and open-tubular capillaries

Abstract: La methode de separation electrocinetique donnee peut etre consideree comme un type de chromatographie de partage liquide-liquide ne necessitant pas de support solide pour maintien de la phase liquide stationnaire, et dans laquelle les micelles sont considerees comme une pseudo-phase

Ferrocene-mediated enzyme electrode for amperometric determination of glucose.

Abstract: for each type of enzyme but in an opposite direction for each. The type III enzyme experiences an increase in apparent Km with increasing inosine concentration, while the type V enzyme shows a slight decrease in apparent Km at high inosine concentration. The most dramatic homogeneous effect is that of increasing inosine concentration upon the VmM values, however. For the type III enzyme, apparent VmiU! is reduced by nearly a factor of 2 but, for the type V enzyme, apparent Vma, decreases more than 7-fold. Such product inhibition reveals itself through longer response times in the immobilized enzyme electrodes. The results obtained in this study show that the potentiometric ammonia gas-sensing enzyme electrode does exhibit linear responses to substrate concentrations both above and below the Km value of the adenosine deaminase enzyme when sufficient enzyme is immobilized at the electrode surface. The BSA-glutaraldehyde cross-link provides for stabilization of the enzyme activity as shown by the observed electrode lifetime. Comparison of the homogeneous kinetic parameters with those obtained from the immobilized study reveals significant changes in the kinetic properties of the enzyme when it is immobilized, possibly resulting from conformational changes in the enzyme upon exposure to BSA and glutaraldehyde. The magnitude of the effect of addition of inosine on apparent Km and Vmax depends upon whether the enzyme is immobilized or free in solution. The apparent Km for the immobilized enzyme remained essentially constant upon addition of inosine, while the apparent Km for the homogeneous enzyme did show some variation but in opposite direction for the type III and V enzymes. In the construction of enzyme electrodes, it is desirable to obtain the highest (fastest rate) and lowest Km (greatest affinity) values possible. From the results of this study carried out at high enzyme levels it is apparent that type III adenosine deaminase would be the best choice for the construction of an immobilized enzyme electrode both from the point of view of apparent Km and Vmax values and from the less pronounced product inhibition effect on the type III enzyme compared to the Type V enzyme. Even in the absence of initial inosine, type III enzyme electrodes have faster response times than corresponding electrodes prepared with type V enzyme.

Space charge effects in Fourier transform mass spectrometry. Mass calibration.

Abstract: Developpement d'une nouvelle relation entre la masse ionique et la frequence cyclotron efficace, pour des ions stockes dans une cellule cubique et detectes par spectrometrie de masse a transformee de Fourier

Characterization of electrochemically pretreated glassy carbon electrodes

Abstract: Un pretraitement electrochimique nettoie l'electrode de ses contaminants introduit au cours du polissage et entraine une oxydation superficielle qui influence certaines reactions

Ultrafast Voltammetry and Voltammetry in Highly Resistive Solutions with Microvoltammetric Electrodes

Abstract: On peut realiser des etudes de voltammetrie cyclique en presence d'electrodes microvoltammetriques, a des vitesses de balayage tres rapides (jusqu'a 100 kVs −1 ) ou dans des solutions a forte resistivite par suite d'une chute ohmique reduite et de la capacite de la double couche

Monodisperse aerosol generation interface for combining liquid chromatography with mass spectroscopy

Abstract: L'interface permet des limites de detection de l'ordre du nanogramme. Il comprend l'utilisation d'un aerosol monodisperse, l'evaporation du solvant a temperature ambiante et sous une pression proche de la pression atmospherique et l'utilisation de separateurs gaz/solide

Determination of part-per-trillion levels of polychlorinated dibenzofurans and dioxins in environmental samples.

Abstract: The analytical method permits determinations of parts-per-trillion levels and lower of tetrachloro through octachloro congeners of dibenzo-p-dioxins and dibenzofurans in various types of biological tissues and sediments. Preliminary tests also indicated the method is applicable to determinations of tetrachloro through hexachloro congeners of ortho-unsubstituted polychlorinated biphenyls. Interferences both from biogenic and from xenobiotic substances are reduced to extremely low levels. The procedure has an extremely low susceptibility to false-positive determinations which could result from the presence of a wide variety of cocontaminants. A modular approach to contaminant enrichment has permitted the integration of seven processes into a two-step procedure, significantly reducing time requirements and the number of sample manipulations, and making the procedure amenable to automation. The reliability and accuracy of the procedure are demonstrated by the results of intralaboratory and interlaboratory studies and by successful analyses of over 200 samples of a wide variety of types.

Surface-enhanced Raman spectrometry for trace organic analysis

Abstract: The analytical potential of a new spectrochemical method based on surface-enhanced Raman spectrometry (SERS) on silver-spheres-coated substrates is presented for the first time in this work. A new method for preparing SERS-active substrate using submicron size silver-coated spheres deposited on filter paper substrates is described in detail. The analytical figures of merit and limitations of the technique are discussed. The detection limits for several organic compounds such as carbazole, 1-aminopyrene, and benzoic acid are 0.2, 1.4, and 0.3 ng, respectively. The results indicate that SERS shows great promise as a useful analytical tool for trace organic analysis.

Fiber-optic probe for in vivo measurement of oxygen partial pressure.

Abstract: Cette sonde est basee sur le quenching a fluorescence et consiste en 2 brins de 250 μm de fibre optique plastique se terminant par une section de polymere poreux de 3 mm de long et 0,6 de diametre

Ion-exchange selectivity of Nafion films on electrode surfaces

Abstract: : Films of 1100 EW Nafion were coated onto glassy carbon electrode surfaces and these chemically modified electrodes were used to characterize the ion exchange selectivity of the polymer. This was accomplished by allowing electrodes to equilibrate with solutions of various electroactive counterions and then determining the quantity of ion incorporated into the films coulometrically. These data were used to calculate both ion exchange partition and selectivity coefficients. Ion exchange selectivity coefficients (vs. Na(+)) for hydrophobic, organic counterions were very large (10,000 to 6 x 6,000,000) confirming earlier work which suggested that Nafion preferentially incorporates such counterions. The implications of this unusual ion exchange selectivity to electroanalysis are discussed. (Author)

Applications of microwave oven sample dissolution in analysis

Abstract: Heating in a microwave oven in the presence of acid mixtures dissolves the metals from powdered coal, fly ash, oil shales, rocks, sediments, and biological materials. The dissolution is complete within 3 min. Nearly 25 elements (Al, As, Ba, Be, Ca, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, P, Pb, Si, Sr, Tl, V, and Zn) from the dissolved samples are determined by inductively coupled plasma emission spectrometry. The method has been tested on a variety of standard reference materials, with reproducible and accurate results.

O-Phtalaldehyde derivatives of amines for high-speed liquid chromatography/electrochemistry

Abstract: Les amines peuvent etre analysees par chromatographie apres reaction avec l'o-phtalaldehyde et des thiols. Divers thiols sont testes afin d'obtenir les derives les plus stables

Model for micellar effects on liquid chromatography capacity factors and for determination of micelle-solute equilibrium constants

Abstract: A three-phase equilibrium model relating capacity factor to micellar mobile phase concentration in liquid chromatography is proposed, and equations are developed which allow calculation of the equilibrium constant for the solute between the bulk aqueous phase and micellar aggregate. In addition, if the equilibrium constant is available from independent methods, the equations can accurately predict the chromatographic capacity factor at zero or greater mobile phase micelle concentration. The elementary model described here assumes minimal electrostatic interactions and is suited for application to neutral solutes; however, it is possible to extend it to account for other simultaneous equilibria such as prototropic. The two principal equilibria for the solute are bulk phase-micelle and bulk phase-stationary phase. A third component, micelle-stationary phase, can be neglected. Use of an equilibrium expression approach permits calculation of micelle-solute equilibrium constants which are in good agreement with literature values for small to moderate size species, such as naphthalene, and in fair agreement for larger molecules, such as pyrene.

Room-temperature phosphorescence of polynuclear aromatic hydrocarbons in cyclodextrins

Abstract: A new approach for production of phosphorescence at room temperature in fluid solution using microscopically organized media is described. Lumiphors form inclusion complexes inside cyclodextrin molecules and, in the presence of a heavy-atom-containing species, undergo emission from their triplet state. The resulting phosphorescence is intense, spectrally well resolved, and partially insensitive to quenching by dissolved oxygen. Only molecules that physically can enter the cyclodextrin cavity are phosphorescent, which provides considerable selectivity based on lumiphor size. Shapes of analytical calibration curves are similar to those obtained for micelle stabilized room-temperature phosphorescence and are linear over 4 decades. Typical precision is < 10% RSD, with limits of detection in the 10/sup -11/ to 10/sup -13/ M range. Application of the method to the determination of polynuclear aromatic hydrocarbons is discussed. 26 references.

Versatile, efficient Raman sampling with fiber optics

Abstract: Description d'un systeme dans lequel la lumiere laser et la diffusion Raman ont pour support des fibres optiques. Cette technique permet des analyses dans des environnements hostiles

Liquid chromatographic determination of polycyclic aromatic hydrocarbons in air particulate extracts

Abstract: Reversed-phase liquid chromatography (LC) with fluorescence detection was used for the determination of 13 polycyclic aromatic hydrocarbons (PAH) in urban air particulate material as part of the process of certifying this material as Standard Reference Material (SRM) 1649. The fluorescence excitation and emission wavelengths were changed during the chromatographic analysis to optimize the selectivity for individual PAH. A second approach was employed which involves normal-phase LC on an aminosaline phase to isolate PAH fractions based on the number of aromatic carbons, followed by analysis of these fractions by reversed-phase LC with UV or fluorescence detection. Results obtained by use of the LC methods are compared with results obtained by gas chromatography. Analytical results obtained by using these LC methods are presented for the analysis of a second urban particulate material (SRM 1648) and a diesel exhaust particulate sample. 38 references, 4 figures, 5 tables.

On-column electrochemical detector with a single graphite fiber electrode for open-tubular liquid chromatography

Abstract: Les solutes sont detectes a l'interieur pres de la sortie d'une colonne capillaire de diametre interieur 15 μm

Phthalocyanine-containing chemically modified electrodes for electrochemical detection in liquid chromatography/flow injection systems

Abstract: Construction d'une electrode a pâte de carbone modifiee chimiquement par le cobalt phtalocyanine et application a l'analyse chromatographique de l'hydrasine

Laser-induced fluorescence of flowing samples as an approach to single-molecule detection in liquids.

Abstract: A flow cytometer system was used to detect aqueous rhodamine 6G by laser-induced fluorescence. Best results were obtained with careful spectral and spatial filtering. At the detection limit, the probability of a rhodamine 6G molecule being present in the detector's probed volume of 11 pL is about 0.6 . With a flow rate of 0.42 ..mu..L/s, a detection limit of 8.9 x 10/sup -14/ M was obtained for a 1-s time constant. At the detection limit, 18 ag or 22,000 molecules of rhodamine 6G flowed through the probed volume during the signal integration period. Signal linearity extends over greater than 5 orders of magnitude limited only by saturation of the detection electronics at high concentration. The results presented here allow a projection to single-molecule detection with reasonable improvements to the apparatus. 25 references, 5 figures, 7 tables.

Model of a two-substrate enzyme electrode for glucose.

Abstract: Dans cette electrode, les enzymes sont immobilisees a l'interieur d'une membrane attachee a un detecteur electrochimique de l'oxygene, cosubstrat de la reaction enzymatique. Le modele mathematique presente concerne les phenomenes de reaction et de diffusion ayant lieu a l'interieur de la membrane