Increased sensitivity potentiometric detectors for FIA

This paper describes the development of potentiometric detection systems with increased sensitivity for flow injection analysis (FIA). The detection systems are based on homogeneous crystalline membranes which are sensitive to chloride, bromide and iodide anions and copper, cadmium and lead cations. Two types of potentiometric detection systems have been established: one has two tubular electrodes sensitive to the same species placed sequentially, in which one of the electrodes works alternatively as a reference electrode (sequential detector system); the other type comprises a tubular potentiometric detector with two membranes and a conventional reference electrode (double membrane detector system). In the latter, totalling the potentials of each membrane is performed externally using an electronic summing device. The behavior of the two detection systems was evaluated in a low-dispersion FIA manifold. Their characteristics were similar to those of single membrane tubular electrodes, except for the calibration slope, for which a value approximately double was obtained.