Determination of inorganic oxyhalide disinfection by-products in bottled water by EPA Method 326.0 for trace bromate analysis

An ion chromatography method with post-column reaction and optical detection, according to EPA Method 326.0, for the determination of bromate has been developed and validated in water samples. Optimization of reaction and operating conditions (post-column reagent and sulphuric acid regenerant flow rate) made possible to minimize the background noise and attain low detection limit. Employing a carbonate elluent (9.0 mM Na2CO3) at a flow rate of 1.1 ml/min and a sample loop of 250 µl, a detection limit for bromate of 0.33 µg/l and a quantification limit (LOQ) of 0.99 µg/l were generated. Under these conditions bromate and chlorite were separated (resolution factor >2.5) in an analysis time of less than 6.5 min and the important validation parameters were evaluated. Calibration curve in laboratory-grade water produced excellent regression in the range from LOQ up to 20μg/l in the order of r2=0.99, whereas a range of applicability of 0.99 μg/l to 100 μg/l was confirmed. UV detector response (AU*min/(μg/l)) was almost constant (± 2%) at various concentration levels. The recoveries obtained in the accuracy test for all aqueous matrices studied were in the 93.1–106% range and the intraday and interday precisions (expressed as coefficient of variation, CV) were smaller than 13.5%. Expanded uncertainty (95%) was calculated at various concentration levels according to propagation error theory (1±0.28 µg/l, 5±0.44 µg/l, 10±0.60 µg/l).

The method presented here represents a rapid and sensitive technique to monitor bromate in a variety of aqueous matrixes derived from different treatment processes in the presence of iodate and chlorite. An ion chromatographic system resolved the bromate anions which combined with a post-column reagent generating the triiodide ion which was detected in a UV detector. The operating parameters of each segment of this process were optimized for maximum sensitivity towards bromate in real samples and synthetic solutions containing a controlled ionic strength. The specific reagent of potassium iodide in the post-column reaction allows for a very specific and sensitive assay for bromate in complex matrices. The method was validated for tap water samples (disinfected and non-disinfected) and the validation parameters (linearity, LOD, LOQ, repeatability, reproducibility, accuracy and selectivity) obtained have shown to be adequate for the determination of bromate. The recoveries obtained in the accuracy test were in the 93–106% range and the intraday and interday precisions (expressed as coefficient of variation) were smaller than 13.5%. A calibration graph was obtained in the 1– 20 µg/l while a range of applicability of 0.99 µg/l to 100 µg/l was confirmed.