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

Flow-through ion-selective electrodes were constructed from compressed pellets (8-10 mm thick, 13 mm diameter, 10 tons/cm(2) pressure) of Ag(2)S/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 x 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 x 10(-5)M I(-), 3 x 10(-5)M S(2-) and 7 x 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 0.1M 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 x 10(-6)M Br(-), 10(-4)M Cl(-) and 5 x 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.

Determination of traces of Zn, Cd, Pb and Cu in white sugar by anodic stripping voltammetry and a modified oxygen-flask combustion technique.

Anodic stripping voltammetry with a hanging-drop mercury electrode is used for determination of traces of Zn, Cd, Pb and Cu in white sugar. The sample (1.5 g) is decomposed by ignition in oxygen in a specially modified system.

Ion exchange method for rapid determination of alkalinity of water-soluble tea ash containing high levels of manganese.

An ion exchange method to determine the alkalinity of water-soluble tea ash containing high levels of manganese is described. A chromatographic column containing a strong cation exchange resin (20-50 mesh) in Na+ form, with a bed volume of 5 mL is used. The present ion exchange method is compared to pH titrations and also to the official AOAC methods (31.012, 31.015, 31.016). Results with the new method are accurate and precise.