Purge-and-membrane mass spectrometry, a screening method for analysis of VOCs from soil samples

Purge-and-membrane mass spectrometry (PAM-MS) is a combination of dynamic h eadspace sampling and membrane extraction. A new and simple purge-and-membr ane sampler is introduced and its basic testing results for the analysis of VOCs in soil samples are reported. Soil moisture had no effect on desorpti on times in the case of sand, but the desorption times increased when the c ontent of organic matter in the soil sample (garden soil) increased. The lo ngest desorption times were measured,with dry garden soil samples. For both types of samples, minor differences in desorption peak areas were observed between 10 and 20% moisture. Detection limits of the VOCs varied in the ra nge 2-150 mug/kg, depending on the soil type. Good linearity (correlation c oefficient > 0.990) was observed in the range 0.5-50 mg/kg. Aging of the sp iked soil samples had only a slight effect on desorption peak areas for sam ples stored at 5 degreesC up to two weeks, but after six months of storing, differences were observed between dry sand and moistened garden soil. In b oth cases, peak areas were diminished. On average, 46% of compounds could b e desorbed from the aged sand and 86% from the aged garden soil. The modifi ed vapor fortification method was used in preparing standard soil samples, which were analyzed by static headspace gas chromatography (HSGC) and PAM-M S. Some authentic soil samples were also analyzed using both of these techn iques. Mangy of the vapor fortification samples and the authentic samples w ere also analyzed in another laboratory by HSGC. The agreement between the methods and the laboratories was generally good.