Reaction processes effecting the analysis of chloroform by direct aqueous injection gas chromatography

Several important reaction processes which influence the analysis of chloroform by direct aqueous injection (DAI) gas chromatography have been identified through an investigation of the chlorination reactions of humic acid and a series of simple polyhydroxyaromatic and diketone model compounds in dilute solution. The reaction of chlorine with each substrate system was studied over the pH range 2–12. Gas chromatographic analysis by the DAI and organic solvent liquid-liquid extraction (LLE) procedures gave different measurements for the yield of CHCl₃ depending on the pH of the reaction solution and the chemical structure of the substrate. Under acidic and neutral conditions, a variety of trichloromethyl-substituted intermediates were identified at high concentrations in addition to chloroform by GC/MS. Chloral hydrate, trichloroacetic acid, pentachloroacetone and hexachloroacetone undergo hydrolysis and/or decarboxylation to form CHCl₃ at the high injection port temperatures employed in aqueous injection GC analysis. The results obtained in the current study indicate that the decomposition of these and structurally-related species accounts for differences previously observed upon application of the DAI and either the LLE or purge-and-trap techniques for the determination of CHCl₃ in chlorinated natural waters.