Comparison of sample preparation methods for the analysis of volatile organic compounds in soil samples: Solvent extraction vs vapor partitioning

Presently, both direct vapor partitioning and solvent extraction methods of sample preparation are commonly used for the characterization of volatile organic compounds (VOCs) in soil. These two approaches of recovering VOCs from this matrix, and other forms of solid waste, are often used interchangeably without any recognition of how different parameters (enviromental and procedural) influence their performance. Three vapor partitioning headspace and three solvent extraction methods of preparing soil samples for the determination of VOCs were compared, without being confounded by volatilization or biodegradation losses. Soil samples were spiked with five aromatic and four chlorinated compounds using two different laboratory procedures. Recovery efficiencies for the preparation methods tested depended on soil organic carbon content, the octanol-water partition coefficients of specific analytes, and the duration of solvent extraction. Overall, methanol extraction was the most efficient and robust method for recovering spiked VOCs. Recovery of VOCs with tetraethylene glycol dimethyl ether and poly(propylene)glycol, as well as three vapor partitioning headspace methods, were frequently less than that obtained with methanol.