Tribromonitromethane (bromopicrin), dibromochloronitromethane, bromodichloronitromethane, and trichloronitromethane (chloropicrin) have been identified as drinking water disinfection byproducts (DBPs). They are thermally unstable and decompose under commonly used injection port temperatures (200-250 ℃) during gas chromatography (GC) or GC/mass spectrometry (GCIMS) analysis. The major decomposition products are haloforms (such as bromoform), which result from the abstraction of a hydrogen atom from the solvent by thermally generated trihalomethyl radicals. A number of other products formed by radical reactions with the solvent and other radicals were also detected. The trihalonitromethanes also decompose in the hot GC/MS transfer line, and the mass spectra obtained are mixed spectra of the undecomposed parent compound and decomposition products. This can complicate the identification of these compounds by GCIMS. Trihalomethyl compounds that do not have a nitro group, such as tribromoacetonitrile, carbon tetrabromide, methyl tribromoacetate, and tribromoacetaldehyde, do not decompose or only slightly decompose in the GC injection port and GC/MS transfer line. The brominated trihalomethyl compounds studied also showed H/Br exchange by some of their fragment ions. This H/Br exchange also makes the identification of these compounds in drinking water more difficult. The extent of H/Br exchange was found to depend on the mass spectrometer ion source temperature, and it is proposed that the internal surface of the ion source is involved in this process.
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