Abstract
A method for the coulometric detection of silicate, phosphate, and germanate ions with the molybdoheteropoly acids after the separation with anionexchange chromatography was investigated. The size of the separation column used was 9mm in inside diameter and 80mm in length, and strong base anion exchange resin was packed in the column. Good results was obtained when 0.4M NaOH was used as the eluent for the separation of silicate and germanate ions, and 0.4M NaOH-0.02M Na2SO4 for silicate and phosphate ions. The optimum conditions for the coulometric detection of these ions are the following : the working electrode potential kept at 0.10 V vs. ferri-ferrocyanide, H2SO4 concentration in (0.4±0.1) N, and reaction time for 5min at 40°C. The detection limit was 0.2ppm (0.1μg, as Si and P) for silicate and phosphate ions. The linear dynamic range was (0.2250)ppm (as P) for phosphate and (0.250)ppm (as Si) for silicate. And the coefficient of variation at 50ppm {ca. 200ppm (as Ge) for germanate} was less than 2% for these three ions. Alkaline earth and heavy metal ions more than 1000ppm interfered the determination because of their co-precipitation. Ions of As (V), Sb (V) and Cr (VI), however, did not interfere the detection. The method is useful for the determination of ppm level of these ions in water.
