Determination of chromate ion in chromium plating baths using capillary zone electrophoresis with micellar solution

Abstract

Chromate anion (CrO 2− 4) has been determined by capillary zone electrophoresis with on-column UV detection at 273 nm by using a negative power supply. A fused-silica capillary (53 cm × 0.05 mm I.D.) was employed and a high voltage of 20 kV was applied. The addition of a cationic surfactant, tetradecyltrimethylammonium bromide (TTAB) in the buffer solution reverses the direction of the electroosmotic flow (EOF) in the capillary, so that EOF augments the mobility of the anion. This results in an exceedingly short analysis time of under 2 min. From migration time data, the electroosmotic mobility, the electrophoretic mobility of the micelle and apparent electrophoretic mobility of the chromate ion in the micellar solution were determined as a function of the concentration of TTAB. Linear calibration for chromate ion was established over the concentration range 25–300 pg with a detection limit of 1.2 pg/nl by using a 0.01 M carbonate buffer and 5 m M TTAB solution (pH 10). The method was applied to the determination of the chromate anion in a rinse water from chromium plating baths.