Electrochemical microcell based on silver solid amalgam electrode for voltammetric determination of pesticide difenzoquat

This study presents an application of a non-toxic mercury meniscus modified silver solid amalgam electrode as a reliable, user-friendly and sensitive sensor for the determination of herbicide difenzoquat as a model pollutant in micro volumes of samples. Difenzoquat gave one cathodic peak at around -1.4 V (vs. Ag/AgCl/3 mol L-1 KCl reference electrode) independent on pH (in the range 8-12). Sharp maxima greatly influenced the peak of the analyte and they were eliminated by the addition of gelatine as a surface-active compound. The optimal supporting electrolyte was found to be Britton-Robinson (BR) buffer with pH 12. Determination of the analyte in the 10 mu L volume was carried out in a newly developed simple microcell with the amalgam working electrode. A procedure for fast and reliable removal of dissolved oxygen was used. Difenzoquat was therefore successfully determined by differential pulse voltammetry in BR buffer pH 12 and in model river water samples with addition of gelatine with limits of quantification 0.41 and 0.45 mu mol L-1, respectively. It was proved that this sensor can be directly used for monitoring of pollutants in volumes of tens of microliters of various samples with similar parameters as the determination in larger volumes.