Potentiometric enzyme electrode for urea based on electrochemically prepared polypyrrole membranes

The present study explores the attractiveness of combining flow-injection (FI) with lead hydride generation atomic absorption spectrometry (AAS) to improve the selectivity and sensitivity of analysis. Lead hydride was generated in three acid-oxidant media: HNO₃-(NH₄)₂S₂O₈, lactic acid-K₂Cr₂O₇ and HNO₃-H₂O₂. The effect of chemical parameters (acid-oxidant concentration and NaBH₄ concentration) was investigated and the performance of each generation medium in terms of interferences, sensitivity and detection limits was compared with that obtained in batch mode. In all cases improved sensitivity (HNO₃-H₂O₂, 0.8 ng Pb; lactic acid-K₂Cr₂O₇, 0.2 ng Pb; (NH₄)₂S₂O₈-HNO₃, 4ng Pb) was obtained, most notably in HNO₃-H₂O₂, which provided 12 times higher sensitivity than in batch mode and sharper absorption peaks. Furthermore, interference by Cu and Ni was lower in the proposed FI-HG system. Compared with the batch mode, about 10 to 100 times higher concentrations of interferent are tolerated in the sample. The use of FI also allows work at a lower NaBH₄ concentration. The method was applied to the determination of lead in water samples with a sampling frequency of 180 samples per hour. In terms of both sensitivity and freedom from interferences, lactic acid-K₂Cr₂O₇ was the best of the generation media tested.On leave from the School of Environmental Studies, Jadavpur University, Calcutta 700032, India