Showing papers in "Analytical Chemistry in 1986"

Error propagation and figures of merit for quantification by solving matrix equations

Abstract: La propagation d'erreur et les autres figures de merite sont definis pour chaque composant, si l'on considere la partie du signal orthogonal au spectre des autres composants. Application aux donnees d'absorbance d'un melange de 4 RNA

Generalized rank annihilation factor analysis

Abstract: : The method of rank annihilation is shown to be a particular case of a more general method for quantitation in bilinear data arrays such as LC/UV, GC/ MS or emission-excitation fluorescence Generalized rank annihilation is introduced as a calibration method that allows for simultaneous quantitative determination of all the analyses of interest in a mixture of unknowns Only one calibration mixture is required The bilinear spectra of both unknown and calibration sample must be obtained Bilinear target factor analysis is introduced as a projection of a target bilinear matrix onto another principal component bilinear matrix space Keywords: Multivariate analysis; Principal component regression (PCR); Two-dimensional data; Singular value decomposition; and Pseudoinverse

Mass spectrometry of inductively coupled plasmas

Abstract: The alliance of the ICP with MS shows promise of extending the sensitivity and selectivity of MS to elemental analysis of solutions. Some additional areas of research interest for ICP-MS include the following: its use as an element and isotope selective detector for chromatography, flow injection analysis, laser ablation, and other sample introduction techniques; fundamental studies of ionization other basic processes in the ICP; detection of halogens and perhaps other elements as negative ions; and auxiliary ionization of neutral analyte atoms formed from ICP ions that have recombined with electrons during the extraction process. The latter concept is particularly interesting because the present detection limits for ICP-MS are achieved even though only one analyte ion is detected for every 10/sup 5/ or 10/sup 6/ that would be going through the skimmer if no recombination occurred. 42 references, 6 figures, 2 tables.

Digital Simulation of the Measured Electrochemical Response of Reversible Redox Couples at Microelectrode Arrays: Consequences Arising from Closely Spaced Ultramicroelectrodes

Abstract: Diffusion to arrays of closely spaced (1.2-0.2 pm) ultramlcroelectrodes (50 pm X 2.3 w) was studied by dlgltal dmuiation and by examining the redox behavior of Ru(NH,)~+ in H,O. Cyiindrlcai diffusion of solution species resulted in quasi-steady-state currents at the microband electrodes. Generation-collectlon experlments, analogous to rotating ring-disk collection experhnents, resulted in larger generator currents than those observed at a single microelectrode due to the back diffusion of products to the neighboring mlcroe lectrode. A collection efficiency of 93% was observed for the reoxidation of RU(NH,):+ generated at a central microelectrode 0.2 pm from two fianklng collector mlcroelectrodes. This experlmenl as well as generator-shrgle collector electrode pairs was simulated at a two-dimensional rectangular expandlng grld and yielded results in good agreement wlth the experiment. Predictions of the model that the collection efflclency principally depends on the gap dze, rather than electrode wldth, were tested experimentally. The novel application of microelectrode arrays to the study of the foilow-up reactions of electrogenerated Intermediates is demonstrated. The digital simulation of electrochemistry of ultramicroelectrode arrays is shown here to be successful in predicting the effect of variations in electrode geometry on the current response. Our results on the properties of arrays of closely spaced microelectrodes represent the most complete study where theory can be tested with experiment.

Automated fluorometric method for hydrogen peroxide in air

Abstract: A fluorometric method for measuring H/sub 2/O/sub 2/ vapor in air utilizes peroxidase enzyme to catalyze the reaction in which hydroperoxides cause dimerization of (p-hydroxyphenyl)acetic acid. In a second channel, H/sub 2/O/sub 2/ is selectively decomposed by catalase so that the fluorescence signal is due only to organic hydroperoxides. The difference between the two signals is a measure of H/sub 2/O/sub 2/ vapor. The H/sub 2/O/sub 2/ vapor is collected by means of a glass coil though which air and water flow concurrently. The coefficient of variation is 0.5% at 2.5 parts per billion by volume. The standard deviation of the base line is 10 parts per trillion by volume (pptv) under laboratory conditions. This standard deviation has varied between 3 and 33 pptv during ground-based field missions, and was 70 pptv on aircraft flights. Thirty seconds is required for the signal to change from 10 to 90% of its maximum value. 13 references, 4 figures, 1 table.

Measurements within the diffusion layer using a microelectrode probe

Abstract: Realisation de la resolution spatiale des profils de concentration dans le domaine du micrometre et controle des phenomenes se produisant dans un domaine temporel de l'ordre de la milliseconde

Suppression of analyte signal by various concomitant salts in inductively coupled plasma mass spectrometry

Abstract: The interference on the ionization of cobalt by five salts, NaCl, MgCl/sub 2/, NH/sub 4/I, NH/sub 4/Br, and NH/sub 4/Cl, in an inductively coupled plasma (ICP) is first looked at theoretically, and subsequently the theoretical trends are established experimentally by mass spectrometry (ICP-MS). The interference trends are found to be in the order of the most easily ionized element in the matrix salt, i.e., Na > Mg > I > Br > Cl. Quantitatively the theoretical values for the amount of salt needed to produce a particular interference are 1-2 orders of magnitude higher than the experimentally determined values. The results reported here indicate that ICP-MS is somewhat more susceptible to ionization suppression effects than ICP atomic emission spectrometry. It is also found that the most easily ionized element in the salt dominates the matrix ion spectrum observed from the ICP in the order mentioned above. Total ion current measurements by ICP-MC at solute levels above 1% are complicated by orifice plugging and transport loss of the salt and analyte in the desolvation system for the ultrasonic nebulizer used. 27 references, 7 figures, 3 tables.

Liquid chromatographic determination of amino acids after gas-phase hydrolysis and derivatization with (dimethylamino)azobenzenesulfonyl chloride.

Abstract: L'hydrolyse acide en phase gazeuse permet de reduire la concentration de fond produite par hydrolyse en phase liquide normale de 25%

Polymer Modification of Fiber Optic Chemical Sensors as a Method of Enhancing Fluorescence Signal for pH Measurement

Abstract: The authors have prepared a pH fiber optic sensor based on fluorescence intensity. Fluoresceinamine is incorporated into an acrylamide-methylenebis(acrylamide) copolymer that is attached covalently to a surface-modified glass fiber via thermal or photopolymerization. The sensor gives instantaneous responses and reversible measurements over the pH range of 4.0-8.0 with signal-to-noise ratios of typically 275/1. The results indicate that specific fiber optic chemical sensors can be miniaturized and still retain sufficient signal intensity and stability.

In situ laser activation of glassy carbon electrodes

Abstract: Laser pulses of short duration (10 ns) and high intensity (20 MW cm/sup -2/) can increase the rate of heterogeneous electron transfer at a glassy carbon electrode by 1-3 orders of magnitude. The laser pulse may be delivered in situ, directly in the solution of interest, repeatedly if desired. The heterogeneous electron transfer rate constant, k/sup 0/, for the ferri-/ferrocyanide redox system increases from 0.004 to 0.20 cm s/sup -1/ with laser activation, resulting in the highest k/sup 0/ yet observed for this system on glassy carbon. Laser activation results in minor morphological changes to the surface, as observed by scanning electron microscopy, mainly removal of an apparent layer of carbon microparticles. The technique holds promise as a means to repeatedly activate glassy carbon electrodes in situ, thus circumventing the need for renewal or reactivation by polishing or other ex situ treatments.

Micrometer-spaced platinum interdigitated array electrode: fabrication, theory, and initial use

Abstract: : An interdigitated array (IDA) electrode composed of 40 pairs of 0.3 micrometers thick Pt fingers 3.5 micrometers wide and separated by 2.5 micrometer gaps of insulating borosilicate glass substrate has been fashioned by a modified microlithographic technique. The two IDA is applied to measurement of redox electron conduction through films of poly-Os(bpy)2 (vpy)2 (C1O4)2, poly-CRu(bpy)2 (vpy)2 (C104)2, and Prussian Blue that had been electrochemically deposited over the Pt fingers and in te insulating gaps. Appropriate theory for using the IDA for this purpose is developed. Electrochemically generated luminescence from solutions of Ru(bpy)3 (2+) is also observed with the IDA. (Author)

Neutral carrier based calcium(2+)-selective electrode with detection limit in the sub-nanomolar range

Abstract: Formation du complexe 1:3 Ca ++ /N,N,N',N'-tetracyclohexyl-3-oxapentanediamide La limite de detection de la fonction reponse de l'electrode est environ 100 pM Ca 2+

Surface properties of electrochemically pretreated glassy carbon

Abstract: Etudes par voltammetrie cyclique, de la structure poreuse du carbone vitreux, traite electrochimiquement. Les proprietes des groupes de surface sont caracterisees a l'aide de la reduction catalytique d'oxygene et d'adsorption selective de pyrocatechol

Heterogeneous mechanisms of the oxidation of catechols and ascorbic acid at carbon electrodes.

Abstract: Resultats d'etudes par voltammetrie cyclique de l'oxydation du methyl-4 pyrocatechol, de l'acide ascorbique, de l'acide (dihydroxy-3,4)-benzeneacetique, etc

Determination of boron isotope ratios by thermal ionization mass spectrometry of the dicesium metaborate cation

Abstract: A method for the high-precision determination of the isotopic composition of boron by thermal ionization mass spectrometry of Cs/sub 2/B/sub 4/O/sub 7/ is described. The method is capable of producing isotope ratio analysis with a standard deviation of .012%. Procedures for the separation and chemical isolation of boron from silicates and aqueous solutions are also described. Careful attention has been paid to the analysis of blanks and other procedural artifacts.

Selection of adsorbates for chemical sensor arrays by pattern recognition

Abstract: Pattern recognition techniques were applied to frequency shift data obtained from 27 piezoelectric sensors, formed by coating quartz crystals with 27 different GC stationary phases, tested using 14 analytes. The objective was to determine whether or not the 27 original coatings could be reduced to a subset of coatings without a significant loss of analyte identification information. The amount of information loss with a given decrease in dimensionality and the identity of the coatings in the best subset of coatings was sought. The first seven principal components described almost 95% of the variance in the original data set of 27 coatings. A generally useful procedure is proposed and tested herein that allowed the selection of seven coatings that provided the maximum level of analyte discriminating ability. This procedure allows other factors (cost, reliability, etc.) to enter into the selection process while maintaining maximum analytical power with the fewest sensors. 7 references, 2 tables.

Inductively coupled plasma mass spectrometric detection for multielement flow injection analysis and elemental speciation by reversed-phase liquid chromatography

Abstract: L'echantillon est introduit par nebulisation ultrasonique. Les limites de detection absolues pour l'analyse d'injection en ecoulement varient de 0,01 a 0,1 ng pour la plupart des elements si l'on utilise des injections de 10 μL

Prediction of precise isocratic retention data from two or more gradient elution runs. Analysis of some associated errors

Abstract: Erreurs liees a la fois au concept de «linear solvent strength elution» et a des causes experimentales