IDENTIFICATION OF HALOGENATED COMPOUNDS IN CHLORINATED SEAWATER AND DRINKING-WATER PRODUCED OFFSHORE USING N-PENTANE EXTRACTION AND OPEN-LOOP STRIPPING TECHNIQUE

The formation of byproducts in chlorinated seawater used for drinking water production on three oil installations was investigated with the use of n-pentane and open-loop stripping extraction. The use of capillary gas chromatography (GC) with electron capture detection (ECD) and mass spectrometry (MS) revealed the presence of a great variety of bromine-substituted aliphatic and aromatic compounds in both chlorinated seawater and tap water. Tribromomethane and dibromoacetonitrile were found in tap water in the range of 19-27 mu g/L and 0.9-1.6 mu g/L, respectively, and these major byproducts were most efficiently extracted with n-pentane. However, the open-loop stripping technique was better suited for extraction of halogenated compounds present at the low nanograms per liter level, such as the iodinated trihalomethanes. When using n-pentane for extraction of chlorination byproducts, the formation of artifacts such as 3-bromo-2-methyl-2-butanol and other halogenated C-5 compounds was observed. These compounds were presumably formed from the reaction of excessive halogen with traces of olefins in the solvent. While ammonium sulfate only partly prevented the formation of the artifacts, sodium thiosulfate was efficient as a quenching agent and completely destroyed reactive halogen.