INCREASED SENSITIVITY POTENTIOMETRIC DETECTORS FOR FIA

This paper describes the development of potentiometric detection syste ms with increased sensitivity for flow injection analysis (FIA). The d etection systems are based on homogeneous crystalline membranes which are sensitive to chloride, bromide and iodide anions and copper, cadmi um and lead cations. Two types of potentiometric detection systems hav e been established: one has two tubular electrodes sensitive to the sa me species placed sequentially, in which one of the electrodes works a lternatively as a reference electrode (sequential detector system); th e other type comprises a tubular potentiometric detector with two memb ranes 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 man ifold. Their characteristics were similar to those of single membrane tubular electrodes, except for the calibration slope, for which a valu e approximately double was obtained.