Amperometric detection analyte confirmation

When using photochemical reactions, a gain in fluorescence output or electroactivity not only lowers detection limits but also contributes to confirm an analytical result. Examples are the conversion of diethylstilbestrol to a fluorescent hexahydrophenanthrene (277), and the conversion of fenbendazole to fluorescent species (278). Tlie fluorescence of photoconverted diethylstilbestrol can further be enhanced by a subsequent online postchromatographic derivatization with bisulfite to the highly fluorescent phenanthrenediol (279). Another example of photolytic derivatization is the postchromatographic conversion of penicillins and cephalosporins into electroactive species that can be detected by an amperometric detector (280). 

In order to illustrate the quality of this analytical model, the parameters have been optimised for the detection of ALP in our microchannels. As can be deduced from Fig. 36.10, the currents obtained from these analytical expressions are in very good agreement with the experimental data, and revealed to be valid over a large range of analyte concentrations (here from 0.1 to 100 pM). This model confirms that the measured signals correspond very well to the currents that can be expected for ALP determination in such an amperometric microsensor, and it constitutes a very useful tool for the optimisation of both the microchip features and the parameters of the assay protocols. 

In the recent years, the occurrence of anilines, chloroanilmes, and benzidines in environmental waters has started to be of concern due to their widespread use in various industrial processes. Detection of these compounds is generally carried out with LC-ECD working in the amperometric mode using a glassy-carbon electrode. Problems encountered are similar to those for phenolic compounds and, therefore, confirmation is always necessary by UV, DAD, or, preferably, MS detection [6]. These compounds are also CE amenable and this approach is really promising in the sense of sensitivity and selectivity because humic and fulvic material can be separated from the analytes due to their different migration kinetics. 

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