Study of a glassy carbon electrode in amperometric detection using d.c., normal and differential pulse techniques

The results of a comparative study on d.c., normal pulse and differential pulse techniques applied to anodic amperometric detection at a glassy carbon electrode in a voltammetric flow-through cell are presented. The important aspects examined are response time, linearity, limit of detection and selectivity. It is shown that the d.c. mode is the most favourable as long as no adsorption of oxidation products takes place. If strong adsorption occurs, normal pulse detection is recommended, although the limit of detection is somewhat larger.     

Determination of total sulphur in coal by x-ray fluorescence spectrometry

A precise x-ray fluorescence method for the determination of sulphur in coat. The sample is mixed with calcium oxide and active carbon and is gradually heated to 900°C. After coding, lithium tetraborate and lead oxide are added and a prepared. The Pb M_α line is used as an internal standard for the KK_α line. The results for coal have a relative standard deviation of approximately 1% and exhibit.     

Electrospray tandem mass spectrometric analysis of zeaxanthin and its oxidation products

Carotenoids have been implicated in protection of the eye from light-mediated photo-toxicity caused by free radicals. Under conditions of normal oxidative stress the carotenoids serve as protective antioxidants; however, when the oxidative stress exceeds the antioxidant capacity, carotenoids can be oxidized into numerous cleavage products. The determination and identification of oxidized carotenoids in biological samples remains a major challenge due to the small sample size and low stability of these compounds. We investigated the reaction of various zeaxanthin cleavage products with O-ethyl hydroxylamine to evaluate their levels in a biological sample. For this, a sensitive and specific electrospray tandem mass spectrometry (ESI-MS/MS) was developed, avoiding the classical lower sensitive and specific HPLC-UV and fluorescence absorption methods. Protonated molecules [M + H](+) of carotenoids upon collision-induced dissociation produced a number of structurally characteristic product ions. A series of complicated clusters of product ions differing in 14 (CH(2))and 26 (C(2)H(2))Da was characteristic of the polyene chain of intact carotenoids. All carotenoid ethyl oximes of zeaxanthin cleavage products were characterized by the losses of 60 and 61 Da in their MS/MS spectra. Through the application of the LC/MS/MS method, we identified two oxime derivatives of 3-hydroxy-beta-ionone and 3-hydroxy-14'-apocarotenal with protonated molecules at m/z 252 and m/z 370 respectively, in a human eye sample.     

On the loss of cadmium, antimony and silver during dry ashing of biological material

Summary The loss of cadmium, antimony and silver during dry ashing of marine weeds, mussels and shrimps was studied with the aid of radioactive tracers. Except for antimony all biological material was labelled by uptake of the radioactive tracers by the organisms while still alive. At an ashing temperature of 500° C and below no significant loss by volatilization of these elements occurs. The results obtained at higher temperatures with cadmium show that the behaviour of this element may depend on the composition of the organic material. Retention on the wall of quartz crucibles did not cause serious losses.

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Über den Verlust an Cadmium, Antimon und Silber bei der Trockenveraschung von biologischem Material

Zusammenfassung Mit Hilfe radioaktiver Tracer wurden die Verluste an Cadmium, Antimon und Silber bei der Trockenveraschung von Seetang, Muscheln und Krabben untersucht. Mit Ausnahme von Antimon wurden alle Materialien mit den Tracern durch Aufnahme im lebenden Zustand markiert. Bei Veraschungstemperaturen von 500° C und darunter konnten keine signifikanten Verluste durch Verflüchtigung der Elemente festgestellt werden. Das Verhalten von Cadmium bei höheren Temperaturen kann von der Zusammensetzung des organischen Materials abhängen. Verluste durch Haften an der Wand des Quarztiegels waren unbedeutend.

     

The structure of the ion pairs of the carbanion of indene with alkali metal cations

NMR spectra have been measured of the Li⁺, Na⁺ and K⁺ ion pairs of the indenyl carbanion in 1,2-dimethoxyethane and tetrahydrofuran as a function of temperature. The changes of the chemical shifts are explained in terms of the detailed structure of the ion pairs. The results in both solvents strongly suggest that in indenyl-Li⁺ the counterion is predominantly located over the six-membered ring. In THF the preferred position of the cations Na⁺ and K⁺ in the contact ion pairs seems to be the five-membered ring.     

Determination of mitomycin C in plasma, serum and urine by high-performance liquid chromatography with ultra-violet and electrochemical detection

The performance of a number of normal phase and reversed-phase systems, with ultraviolet detection at 360 nm, has been investigated with respect to their applicability to pharmacokinetic studies of mitomycin C (MMC). The reversed-phase system developed was also combined with a polarographic detector in order to compare the sensitivity and selectivity of ultraviolet and electrochemical detection. A simple isolation procedure, based on the adsorption of MMC on a non-ionogenic resin, has been developed. The developed assay is applied to a pharmacokinetic study from which some examples are given.     

N2O decomposition over Fe/ZSM-5: reversible generation of highly active cationic Fe species

Fe-oxide species in Fe/ZSM-5 (prepared by chemical vapor deposition of FeCl3)--active in N2O decomposition--react with zeolite protons during high temperature calcination to give highly active cationic Fe species, this transformation being reversible upon exposure to water vapor at lower temperature.     

Erfahrungen mit der Automatisierung der massenspektrometrischen Gasanalyse

Zusammenfassung Apparatur und Analysengang für die massenspektrometrische Analyse von Gasgemischen mit bis zwanzig Komponenten unter Benutzung eines analog-to-digital converter und einer elektronischen Rechenmaschine werden beschrieben. Die Methode wird mit der normalen massenspektrometrischen Analyse mit photographischer Registrierung der Peaks verglichen, vor welcher sie bei gleicher Genauigkeit den Vorteil größerer Schnelligkeit hat.     

Lateral interactions and multi-isotherms: nitrogen recombination from Rh(111)

Lateral adsorbate-adsorbate interactions result in variation of the desorption rate constants with coverage. This effect can be studied in great detail from the shape of a multi-isotherm. To produce the multi-isotherm, the temperature is increased in a (semi)stepwise fashion to some temperature, followed by maintaining this temperature for a prolonged time. Then, the temperature is stepped to a higher value and held constant at this new temperature. This cycle is continued until all of the adsorbates have desorbed. Using a detailed kinetic Monte Carlo model and an optimization algorithm based on Evolutionary Strategy, we are able to reproduce the shape of the experimentally measured multi-isotherm of nitrogen on Rh(111) and obtain the lateral interactions between the nitrogen atoms.