Simultaneous amperometric and potentiometric detection of inorganic anions in flow systems using platinum and silver/silver chloride electrodes

Platinum and silver/silver chloride electrodes were evaluated for electrochemical detection (amperometry and potentiometry, respectively) of inorganic anions in flow systems. In flow injection analysis, a linear response over three decades and detection limit of 1 × 10−7 M for I− and NO2− were obtained at an applied potential of +0.9 V (vs. AgAgCl) in 30 mM phosphate buffer at pH 3.0 as carrier. A silver/silver chloride electrode responded potentiometrically to halides and pseudo-halides in this buffer with a detection limit of 1 × 10−5 M. The detector, which included both detection systems, was coupled with ion chromatography. Following separation by anion-exchange chromatography with 40 mM phosphate buffer at pH 4.5 as eluent, Cl−, Br−, I−, SCN−, and S2O32− were determined potentiometrically with a detection limit of 1 × 10−5 M, and, simultaneously, NO2−,Br−, I−, and SCN− were determined amperometrically with a detection limit of 1 × 10−6 M. Ion-interaction chromatography with an eluent of 20 mM phosphate at pH 5.0 containing 5 mM tetrabutylammonium hydroxide separated and detected Br−, NO2− and SCN−.