A comparison of sampling techniques for VOCs in soil

Samples (5 g) of an organic soil spiked with a standard volatile organic compound mixture were collected by two methods. One group of samples was weighed upon transfer with a spatula into vials, an aqueous sodium bisulfate solution and a magnetic stirring bar were added and the vial was immediately capped. The other group of samples was obtained with a coring sampler that collected a volume of soil equivalent to 5 g. The sample was immediately transferred into similarly prepared vials. The vials were then sealed with septum-sealed screw caps. Analytes were extracted from the soil matrix using a purge-and-trap technique, SW-846 EPA Method 5035, and then separated, identified, and quantitated by gas chromatography/mass spectrometry SW-846 EPA Method 8260. Samples obtained by means of the coring sampler consistently gave lower recoveries than did those samples that were manually weighed and placed in a sample vial.