Determination of halogenated acetic acids in chlorinated sea water and drinking water produced offshore

The formation of halogenated acetic acids in laboratory chlorinated sea water as well as chlorinated sea water and drinking water produced on an oil-installation offshore was investigated. Analyses were performed using solvent extraction and capillary gas chromatography with electron capture detection and mass spectrometry. Dichloroacetic acid, trichloroacetic acid, dibromoacetic acid and tribromoacetic acid were found in the water samples, with dibromoacetic acid present in the highest concentration (1–6 μg/l). When quenching agents were applied to remove excessive halogen prior to extraction, significantly different concentrations of dibromoacetic acid were observed when samples were quenched with sodium thiosulfate or ammonium sulfate. Sodium thiosulfate quenched samples contained the lowest concentration of dibromoacetic acid and other unidentified products. A stability experiment showed that the presence of sodium thiosulfate did not affect the concentration of dibromoacetic acid in aqueous solutions. The increased levels of dibromoacetic acid in unquenched and ammonium sulfate treated samples is explained by an extended reaction of excessive halogen with organic material in the acid water samples during the time needed for extraction.