Analytical and Bioanalytical Chemistry (v.334, #2)

The determination of mercury in the presence of matrix substances (such as inorganic cations and anions, and organic compounds) was studied by cold vapor atomic absorption spectrometry with „completely continuous micro flow“, using tin(II) chloride in sodium hydroxide solution as reducing reagent. The effects of the diverse substances in the proposed method were found to be much smaller than those in the conventional methods using tin(II) in acid medium or borohydride in alkaline medium as the reducing reagents.

Flame atomization of the solutions resulting from treatment of PVC samples with organic solvents is perfectly feasible. In this work, the organic solutions resulting from treatment of PVC with organic solvents are nebulized, after dilution with acetone. This solvent is miscible with those normally used for dissolving PVC, it does not cause precipitation of the polymer and, in general, gives good performance in the flame. The method is applied to the determination of lead and cadmium in real samples of PVC, and the possible interference arising from the PVC resin and from the presence of other metals in the sample is studied.

Using ion-chromatography it was possible to determine traces of iodide quantitatively without interferences in samples with a high main content of salts. The sensitivity of the procedure could be severely enhanced (factor 150) by the application of a direct photometric detection of iodide at 226 nm in contrast to the normally used conductivity or indirect UV detection. Further advance of the method is due to the fact that nearly no pretreatment of the samples was necessary compared with other methods for the trace analysis of iodide. The detection limit for the direct iodide determination in pure solutions was about 10 ppb, with possible decrease by pre-concentration procedures of aqueous samples.

In addition to their properties of being able to separate organic substance groups, Al2O3 and SiO2 have obviously the ability to bring about an ion exchange. Both of them can be used on thin layers as well as on adsorption columns. Al2O3 provides the anion exchange under the conditions described, while SiO2 brings about the cation exchange. LAS and cation-active surfactants of type DSDMAC, which are nearly always to be found in municipal wastes and sewage sludge, and which often occur in flowing waters, can be very well separated from one another and from accompanying and hazardous substances with the aid of these adsorbents. Even detergents and other technical mixtures which contain surfactants can be decomposed into separate components (substance groups) and analyzed. It can be assumed that Al2O3 and SiO2 can also bring about the ion exchange for other ionogenic substances.

A simple method for the determination of five chlorophenoxyalkane carboxylic acids in cereals is described. After alkaline hydrolysis the samples are extracted on-line. The acids are methylated and cleaned up over small silicagel columns. The gaschromatographic determination is performed using packed and capillary columns. The recovery yields are between 86% and 100%.

The possibility of predicting the parameters in HPLC by means of theoretical calculations, represents a significant step forward in the analysis of the complex mixtures of higher boiling petroleum fractions. Quantitative structure-property relationship, QSPR, is being used more and more in Chromatographic studies, since it is by now established that the retention indices have a structural origin. In the present paper we investigate whether the HPLC parameters of alkanes could be predicted from the QSPR-type models using the Wiener number as a structural descriptor. The Wiener number, which has already been applied in several cases to the prediction of gas Chromatographic retention indices and HPLC parameters for polycyclic aromatic hydrocarbons, has now been employed for calculating the HPLC retention time of n-alkanes and cycloalkanes.

Different oil samples, produced by hydrocracking of vacuum residues, have been characterized by proton NMR spectroscopy. The distribution of various types of carbons and several average structural parameters have been calculated. The analytical data have been correlated with the physical parameters and the hydrogen uptake during the hydrocracking. The results provide information about the course of the hydrogenation reaction.

CuInS2 is one of the important I–III–VI2 ternary compounds which has in recent years received increasing interest in semiconductor science. In this study an electrochemical method has been developed based on a limited amount of available sample (0.5–10mg) for the precise and accurate determination of CuInS2 composition. After decomposition of the sample in concentrated HNO3 under pressure, copper and indium were sequentially determined by constant potential coulometry, and sulfur (as sulfate) by amperometric titration. Various experimental parameters which ensure high precision and accuracy of the results were carefully evaluated and calibrated. The overall errors for the determination of copper, indium and sulfur in a 10 mg sample were found to be +0.10%, −0.12% and +0.16%, respectively, which fullfills the requirement for accurate stoichiometric assessment.

The determination of indium in heavily doped gallium arsenide (0.2–1.2 mg g−1 In), by both electrothermal and flame AAS is reported. The sample is first decomposed with nitric acid and the diluted solution is atomized by employing the more convenient technique. The conventional air-acetylene flame is used for samples containing at least 1 mg g−1 indium. For lower concentrations the electrothermal atomization is required and matrix-matched standards become necessary. Platform sampling is shown to improve both sensitivity and repeatability in comparison with the tube-well sampling. Dependence of the matrix effect on both the signal measurement mode and deterioration of the platform is examined. By increasing the sample mass up to 100 mg, without further dilution of the solution to be injected into the furnace but with the optical correction of the background, a detection limit (6 s) of 4.2 ng g−1 (1.2×1014 atoms cm−3) is achieved. The method was applied to In doped GaAs samples and the results are compared with those independently obtained by differential pulse polarography.

A newly developed apparatus was used for the determination of carbon in pure and high-purity iron samples. It enables the differentiation between the carbon content of the surface and the bulk by temperature-controlled heating in an oxygen flow. The carbon dioxide formed was measured by an IR-gas analyzer, type BINOS. At sample weights of about 0.1 g with surface areas of about 0.5 cm2, carbon concentrations of ≥0.04 Μg/cm2 of the surface and of ≥0.2 Μg/g of the bulk can be determined. By means of the results on 6 certified reference materials with low carbon concentrations and on 7 high-purity iron samples, the influence of sample form, treatment and storage on surface and bulk carbon is demonstrated. The findings confirm the already formerly stated tendency to too high values in the certificates of reference samples with carbon concentrations in the lower Μg/g range.

The polarographic behaviour of 10-chloro-11b-(2-chlorophenyl)-2,3,7,11b-tetrahydrooxazolo[3,2-d][1,4]-benzodiazipine-6(5H)-one (cloxazolam) was studied in the pH range 1–12. Cloxazolam suffers a hydrolysis process, which can be followed by polarography. The reduction processes of cloxazolam and its hydrolysis product are irreversible and their currents are diffusion-controlled. Two polarographic methods have been developed upon the basis of the reduction of both the protonated iminium form (pH 1.45, measurement time: 10 min) and the benzophenone produced in the hydrolysis process (pH 11.75, measurement time: 15 min). The relationship between reduction peak current and concentration is linear up to at least 5.72×10−5 mol/l for both methods. A higher sensitivity was obtained for the method based on the benzophenone reduction (detection limit 5.72×10−8 mol/l; 20 ppb). The methods developed were applied to the determination of cloxazolam in its pharmaceutical formulations (Betavel, 1 mg). The method in alkaline medium was the most adequate for the determination of the compound in tablets, with errors lower than 1%.

This work describes the development of the first optical pH-sensor capable of measuring pH-values in the 0–7 range. The pH-sensitive material consists of fibrous amino-ethyl cellulose onto which fluorescein and eosin were covalently immobilised. Fluorescein was immobilised via its isothiocyanate, and immobilised eosin was obtained by bromination of the immobilised fluorescein. The material thus obtained was mechanically fixed at the end of a bifurcated optical fibre bundle. Fluorescence was excited at 490 nm and measured at >540 nm. The accuracy of the sensor is ±0.05 pH units, its response time ranges from 25 to 30 s. Practically no signal loss was observed upon constant illumination over periods of more than 15 h.

Controlled adsorptive accumulation of Mo(VI)-2-BIBH at the hanging mercury drop electrode (HMDE) provides the basis for the direct stripping measurement of Mo(VI) in nanomolar concentration. The cathodic stripping response is evaluated with respect to experimental parameters such as preconcentration time, preconcentration potential and others. A differential pulse cathodic stripping voltammetric method for the determination of Mo(VI) with 2-BIBH in urine is proposed. The detection limit is 10−9 mol/l Mo(VI), standard deviation for 5×10−8 mol/l is ±1.58×10−9 mol/l.

New books (169-170).

2.7 Pesticides (200-202).