Simultaneous determination of Cl −, Br −, I − and F − with flow-injection/ion-selective electrode systems

Abstract

Flow-through ion-selective electrodes were constructed from compressed pellets (8–10 mm thick, 13 mm diameter, 10 tons/cm 2 pressure) of Ag 2S/AgX (X = Cl −, Br − or I −) drilled longitudinally (1.5 mm diameter hole) to be suitable for use in flow-injection analysis. A column of AgCl (5.5 cm long, 2–3 mm i.d.) was included in the Cl −-electrode manifold to remove interferences from 10 −4 M Br − and 3 × 10 −5 M I − and S 2−. A column of amalgamated lead (2–3 cm long, 2–3 mm i.d.) was used in the Br − electrode manifold to remove interference from 2 × 10 −5 M I −, 3 × 10 −5 M S 2− and 7 × 10 −4 M Cl −. These columns and the addition of ascorbic acid were not required when I − was determined with the iodide electrode. The carrier stream was 0.1 M sodium perchlorate (pH 4) at a flow-rate of 0.5 ml/min. The sample pH could be 4–7. Simultaneous determination of Cl − and I −, Cl −, I − and Br − and Cl −, I −, Br − and F − ions was possible with combinations of the corresponding electrodes and columns in series and/or parallel in specially designed manifolds. Calibration plots were linear, with almost theoretical slopes, down to 10 −6 M I −, 5 × 10 −6 M Br −, 10 −4 M Cl − and 5 × 10 −6 M F −, with precision better than 1%. Sampling rates for single-ion determinations were 72, 102, 90 and 80 per hr for the one-, two-, three- and four-electrode systems respectively. Determinations of these ions in water samples by the recommended procedure and by established batch methods showed no significant difference at the 95% confidence limits in a paired comparison t-test.