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INFLUENCE OF REAGENT PURITY ON THE ION CHROMATOGRAPHIC DETERMINATION OF BROMATE IN WATER USING 3,3'-DIMETHOXYBENZIDINE AS A PROCHROMOPHORE FOR PHOTOMETRIC DETECTION
Citation:
Urbansky*, E T. AND S K. Brown*. INFLUENCE OF REAGENT PURITY ON THE ION CHROMATOGRAPHIC DETERMINATION OF BROMATE IN WATER USING 3,3'-DIMETHOXYBENZIDINE AS A PROCHROMOPHORE FOR PHOTOMETRIC DETECTION. JOURNAL OF ENVIRONMENTAL MONITORING. Royal Society of Chemistry, Cambridge, Uk, 2(6):571-575, (2000).
Description:
Variable availability of the purified dihydrochloride salt of 3,3'-dimethoxybenzidine (DMB, ortho-dianisidine) led us to investigate the effects of reagent purity on the analytical results obtinaed when this reagent is used in the photometric determination of the disinfection byproduct bromate. After analyte ions are separated by ion chromatography, a solution of DMB (post-column reagent) is added to the eluate and the DMB oxidized, thereby producing a chromophore detected by its absorbance. This approach to detection has been referred to as a post-column reaction by some investigators. Although some commercial products of undefined grade performed well, others did not. Variabiity was also observed between lots of purified material. Sensitivity at low concentrations (<5 ug/L-1 BrO3-) varied by a factor of up to 10. In some cases, the lower limit of detection for photometric detection was greater than that obtained using conductivity detection, as high as 5-7 ug/L-1 BrO3-. An impurity or several impurities are believed to be responsible for deviations from linearity at low analyte concentrations. Perhaps these are starting materials or isolable intermediates from the synthesis. This investigation underscores the need for ensuring reagent purity in environmental analyses. Ideally, chemical manufacturers will meet the needs of analytical chemists who test potable water and begin producing a high grade material in sufficient quantities to meet monitoring reuirements. The esablishment of third-party standards for a spectrophotometric grade of DMB 2HCl wold be helpful in ensuring that a variety of manufacturers could supply products of uniformly high quality that would be suitable for the measurement of bromate in public drinking water supplies.