Christos G. Nanos

Phase-transfer catalytic determination of phenols as methylated derivatives by gas chromatography with flame ionization and mass-selective detection

A convenient method for the GC determination of phenols as methylated derivatives is proposed, taking advantage of the beneficial features of phase-transfer catalysis (PTC). The optimal experimental conditions of pH, temperature, organic solvent, time of extraction-derivatization and amounts of the participating reactants and catalysts, were properly established. Several catalysts in soluble or polymer-bound form were tested. Most of them demonstrated appreciably high-performance characteristics but the polymer-bound catalyst is most favourable due to its facile separation from the rest of the reaction system after the extraction-derivatization. Interferences with the extraction and derivatization yield were not noticed. The chromatographic separation of 11 methylated derivatives of phenols was complete within 23 min. The detection limits of the method, which range from 0.005 to 0.120 microg, are inadequate for drinking water analysis. However, the method was successfully applied to the analysis of fortified composite lake water samples using GC-flame ionization detection and GC-MS in the single ion monitoring mode with the most abundant characteristic ions. Spiked recoveries of phenolics were in the range 94-102%, on the basis of distilled water calibration graph, signifying that PTC determination of phenols is not affected by the composition of such matrices.

Ion chromatographic method for the simultaneous determination of nitrite and nitrate by post-column indirect fluorescence detection.

This short paper highlights the suitability of ion chromatography with post-column indirect fluorescence detection to determine simultaneously nitrite and nitrate based on the quenching of tryptophan native fluorescence. The method uses an enhanced fluorescence mobile phase containing tryptophan and detects the suppression of fluorescence of the mobile phase due to the elution of the target ions. The phenomenon of fluorescence quenching of tryptophan is highly induced by the presence of phosphate ions. The quenched fluorescence intensity exhibits concentration dependence in the range 1-25 mg/l and 3-65 mg/l for nitrite and nitrate, respectively. The relative standard deviation for five replicates of a standard solution containing a mixture of 5 mg/l of nitrite and 10 mg/l of nitrate lies around 2.8%. This simple coupling technique results in a relatively sensitive, fast, and accurate method, allowing for both qualitative and quantitative analysis of nitrite and nitrate. The method can easily be implemented to real samples such as foodstuffs, fertilizers and soils and is proven to be precise and accurate when compared with reference methods.

Assay of reducing sugars in beverages, wines, honey and marmalades using potentiometric stripping analysis (PSA)

SummaryIn the proposed method excess of Soxhlet reagent is added to the sugar standard solutions and the unknown samples; the reduction of Cu(II) to Cu2O is taking place by heating at constant temperature for a specified time. Unreduced copper in the supernatant solution or reduced copper in the Cu2O precipitate is determined by PSA. The method offers the following advantages for the determination of reducing sugars in soft drinks, wines, spirituous liquors, honey, marmalades etc.: 1) high sensitivity, due to the PSA-technique; 2) applicability to coloured and turbid samples where the official methods cannot be applied without preceding treatment of the sample; 3) good agreement with standard methods for the assay of sugars.

Decomposition of 2,6-dichlorophenolindophenol in strongly acidic solutions: a potential kinetic method for the determination of pH

The problem of pH measurements at extreme pH values is well known. Higher pH values are obtained at pH values of below 1 because of the so-called ‘acid error’. The acid error depends on various parameters and it is not always reproducible. In order to determine accurate pH values at high acidities, a kinetic study of the decomposition of 2,6-dichlorophenolindophenol (DCPl) in strongly acidic solutions was investigated by applying the stopped-flow technique. The DCPl is unstable at lower pH values (below 2) and the reaction rate constant for its decomposition in the pH range 0–2 is dependent on the pH. A good correlation between pH and the observed reaction rate constant of the decomposition of DCPl (kob) was found for low pH values. The reaction rate constant, k1, was calculated by three different approaches for the evaluation of the experimental data. The weighted mean value of k1 was found to be (77 ± 1)× 10–3 l mol–1 S–1, with confidence limits of 95%. A knowledge of k1 is also important in analysis as DCPl is the main reagent for the determination of assorbic acid in acidic solutions.