Sequential injection determination of chromium(VI) by transient oxidation of brucine with spectrophotometric detection and in-line dilution

Abstract

A sequential injection method for the determination of chromium(VI) in residual waters from electroplating baths and steels is proposed. The method is based on monitoring the absorbance at 525 nm due to an aminochrome intermediate compound resulting from oxidation of the alkaloid brucine. The intermediate brucichrome is unstable so that its analytical use is only possible in closed flowing systems where the precise and reproducible control of time and mixing is possible. The method gave a linear calibration curve from 0.2 to 2 mg l^–1 Cr(VI) and a detection limit of 0.045 mg l^–1 Cr(VI). A sampling frequency of 120 h^–1 is possible. Industrial samples from electroplating baths and residual washing waters were analyzed, and in this case a sequential injection in line dilution was performed, permitting real time determination of samples with Cr(VI) concentrations up to 100 mg l^–1 with a sampling frequency of 80 h^–1.