Ion chromatography determination of trace level bromate by large volume injection with conductivity and spectrophotometric detection after post column derivatisation

Abstract

Bromate is a well known by-product produced by the ozonisation of drinking water; the allowed concentration for human consumption has to be regulated to the low μg l −1 range. A direct injection, ion chromatographic method was developed using a tetraborate eluent with serially connected conductivity and spectrophotometric detection. Bromate was detected after post-column reaction with fuchsin at 520 nm. Sample capacity was investigated by injecting large volumes (up to 6 ml) using a high total hardness and chloride tap water. Linear correlation of bromate response with volumes from 1 ml to 6 ml was demonstrated, the main limitation being the overlapping of the chloride peak with bromate. Up to 1.5 ml sample can be injected without any pre-treatment. With more than 1.5 ml injection volume, a sample pre-treatment with a cartridge in Ag and H form, followed by a 10 min degassing in an ultrasonic bath, was needed. This method was validated by analysing secondary reference materials and real samples from a drinking water treatment plant. The method was linear from the limit of quantification to 20 μg l −1. Reproducibilities in tap water were 18% (5 μg l −1, n=12) and 21% (1 μg l −1, n=4) respectively for 1.5 and 6 ml injection volumes with conductivity detection, and 17% at 0.5 μg l −1 ( n=9) with spectrophotometric detection. Calculated detection limits were 0.5 μg l −1 (6 ml) and 2 μg l −1 (1.5 ml) for conductivity detection and 0.3 μg l −1 (1.5 ml) for spectrophotometric detection.