Volatile Organic Compounds: Comparison of Two Sample Collection and Preservation Methods

Abstract

Two soil sample collection and preservation methods for volatile organic compounds, used during site characterization activities, were evaluated using standard U.S. Environmental Protection Agency analyti cal methods. A conventional bulk method recom mends completely filling a sample container with soil; a less commonly used methanol method recommends placing a soil aliquot into methanol. Analytical results showed large negative biases associated with the bulk samples as compared to the methanol samples for aromatic compounds. Order of magnitude differences in concentrations measured between the methods were observed for benzene and toluene. Lesser differences were noted for xylenes and ethylbenzene. Limited data for chlorinated compounds suggest behavior similar to the aromatic species. A limited spike recovery study was conducted using the methanol method on laboratory and field samples. Samples were analyzed 82 days after spike addition. Poorer spike recoveries were noted from spiked methanol vials transported to the field and used for collection of soil samples. Differences between mean recovery values for the laboratory and field samples appear to be the result of losses during sample collection and transport. Despite the 82-day holding time, spike recoveries were within 70% of initial spike concentrations. These results demonstrate the stability of using methanol as a preservative for soil samples.