Liquid-phase microextraction–gas chromatography–mass spectrometry for the determination of bromate, iodate, bromide and iodide in high-chloride matrix

In the determination of bromate and iodate, any free bromide and iodide present was quantitatively removed by anion exchange with silver chloride exploiting the differences in silver salts solubility product, being AgCl, 1.8 × 10−10, AgBr, 5.0 × 10−13, AgI, 8.3 × 10−17, AgBrO3, 5.5 × 10−5 and AgIO3, 3.1 × 10−8. The oxyhalides were reduced with ascorbic acid to halides and converted to 4-bromo-2,6-dimethylaniline and 4-iodo-2,6-dimethylaniline by their reaction with 2-iodosobenzoate in the presence of 2,6-dimethylaniline at pH 6.4 and 2–3, respectively. Single drop microextraction (SDME) of the haloanilines in 2 μl of toluene and injection of the whole extract into GC–MS, or liquid-phase microextraction (LPME) into 50 μl of toluene and injection of 2 μl of extract, resulted in a sensitive method for bromate and iodate. The latter method of extraction has been found more robust, sensitive and to give better extraction in shorter period than SDME. Total bromine/iodine was determined without any treatment with silver chloride. High concentration of chloride in the matrix did not interfere. A rectilinear calibration graph was obtained for 0.05 μg–25 mg l−1 of bromate/bromide and iodate/iodide, the limit of detection were 20 ng l−1 of bromate, 15 ng l−1 of iodate, 20 ng l−1 of bromide and 10 ng l−1 of iodide (by LPME in 50 μl of toluene). The method has been applied to seawater and table salt. From the pooled data, the average recovery of spiked oxyhalide/halide to real samples was in range 96.7–105.7% with RSD in range 1.6–6.5%.