Sequential and simultaneous determination of bromate and chlorite (DBPs) by flow techniques: kinetic differentiation.

3-3'-Dimethoxybenzidine (o-dianisidine, ODA) is oxidised by Br(2), among other oxidants, generating a compound that absorbs at 450 nm, while the non-oxidised reagent absorbs in the UV region. This reaction has been used previously as the basis of a continuous-flow method for the determination of bromate in ozonised water, with a detection limit lower than the maximum permitted for drinking water (10 microg L(-1)). The only interference observed in the method was that due to the chlorite ion (ClO(2)(-)), which generated the same ODA bromation product. Thus, in systems in which O(3) is employed as a disinfectant and disinfection is later enhanced with ClO(-) and ClO(2), there exists the possibility of finding BrO(3)(-) and ClO(2)(-), oxoanions generated as subproducts. The kinetic behaviour of the reaction between bromate and chlorite with bromine in acidic medium is different, allowing the proposal of a continuous-flow method for the simultaneous or sequential determination of both subproducts in water purification systems. None of the other subproducts interfered in the reaction. Kinetic differentiation was achieved by combining the temperature of the reaction and the length of the coils, after which it was possible to determine both analytes sequentially within a concentration range of 6-160 microg L(-1).

Online monitoring of bromate in ozonized water without a previous separation process.

The use of ozonation for the purification of drinking water can lead to the formation of bromate. The US Environmental Protection Agency and the European Directive for human drinking water has lowered the regulatory level for bromate down to 10 microg l(-1), such that methods must be developed for monitoring the formation of bromate, particularly in on-site situations. In the present work we report a fluorometric method for the determination of bromate based on the reaction with carbostyril-124, a compound that shows fluorescence mainly at pH values above 4 and, when bromated, generates a non-fluorescent product. The reaction can thus be used as an indirect method for determination of the ion. The proposed method, which uses the flow injection (FI) technique, allows online application and kinetic control of the variables affecting the process, together with shorter reaction times, and it provides maximum sensitivity and selectivity. Under optimum conditions, it is possible to determine the analyte within the 4-200 microg l(-1) range, with a limit of detection of 0.9 microg l(-1) and a relative standard deviation (n=12, [BrO3-]=5 and 30 microg l(-1)) of 3.2% and 2.6% respectively. The determination rate was ten samples per hour.