Three soils and two humic materials were extracted with n ‐pentane by supercritical gas extraction. The extracts contained a variety of compounds separated by chemical and gas chromatographic techniques and identified by gas chromatography‐mass spectrometry. The compounds identified in the extracts included n ‐alkanes (ranging from n ‐C 12 to n ‐C 32 ), with n ‐C 26 , and n ‐C 24 alkanes in prominence, and smaller amounts of cyclic alkanes (C 19 to C 31 ). The major components, however were n ‐fatty acids ( n ‐C 7 to n ‐C 29 ), accompanied by lesser amounts of branched fatty acids (C 12 to C 19 ), and unsaturated fatty acids ( n ‐C ‐ 16 , n ‐C ‐ 18 and n ‐C ‐ 18 ). hydroxy‐fatty acids (C 12 to C 16 ), and alkanoic α,ω‐diacids (C 15 ‐C 25 ). The overall even‐to‐odd preference indexes for the n ‐alkanes and n ‐fatty acids were 1.35 and 4.15, respectively, suggesting microbiological origins for these compounds. Total alkanes extracted from the soils and humic preparations ranged from 4.3 to 8.9 and 32.5 to 201.4 mg/kg, respectively. By contrast, alkanoic acids extracted varied from 94.5 to 208.9 mg/kg for the soils and 740.1 to 1576.6 mg/kg for the humic materials. Supercritical gas extraction appears to be a promising procedure for the relatively mild and efficient extraction of specific organic components from soils and humic materials.
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Schnitzer et al. (1986) studied this question.