STATIC AND DYNAMIC HEADSPACE ANALYSIS OF VOLATILE ORGANIC-COMPOUNDS IN SOILS

Dynamic headspace analysis, or purge and trap, is widely used in the United States for volatile organic compounds (VOCs) in soils because several Environmental Protection Agency (EPA) methods specify this approach. In this study, alternative methods based on static headspace analysis were developed and compared to purge and trap. Analyte recovery and method precision were quantified for nine VOCs, including both halogenated aliphatics and nonhalogenated aromatics, and five dissimilar soils. Direct headspace analysis of a soil sample/water slurry with equilibration for 1 h at 95-degrees-C was found to provide recovery and precision superior to that obtained with purge and trap for most soil/analyte combinations. This method produced inferior recovery for a very high organic matter (80%) soil, but this could be improved by agitating the sample during the equilibration period. For the heaviest analytes, direct headspace analysis with agitation was comparable to purge and trap for this atypical soil. Methanol extraction of the soils, as recommended by EPA for high-concentration samples, was found to produce very poor analytical precision. Sample throughput was greater using headspace, primarily because the method could be easily automated for 24-h unattended operation.