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

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 mu g l(-1) range. A direct injection, ion chromatographic method was developed using a tetraborate eluent with serially connected conductiv ity and spectrophotometric detection. Bromate was detected after post-colum n reaction with fuchsin at 520 nm. Sample capacity was investigated by inje cting large volumes (up to 6 ml) using a high total hardness and chloride t ap water. Linear correlation of bromate response with volumes from 1 ml to 6 ml was demonstrated, the main limitation being the overlapping of the chl oride peak with bromate. Up to 1.5 ml sample can be injected without any pr e-treatment. With more than 1.5 mi injection volume, a sample pre-treatment with a cartridge in Ag and H form, followed by a 10 min degassing in an ul trasonic 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 mu g l(-1). Reproducibilities in tap water were 18% (5 mu g l(-1) n = 12) and 21% (1 mu g l(-1), n=4) respectively for 1.5 and 6 ml injection volumes with conduct ivity detection, and 17% at 0.5 mu g l(-1) (n=9) with spectrophotometric de tection. Calculated detection limits were 0.5 mu g l(-1) (6 ml) and 2 mu g l(-1) (1.5 ml) for conductivity detection and 0.3 mu g l(-1) (1.5 ml) for s pectrophotometric detection. (C) 1999 Elsevier Science B.V. All rights rese rved.