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Supercritical Fluid Extraction of 2,4‐D from Soils: pH and Organic Matter Effects
Author(s) -
Rochette E. A.,
Harsh J. B.,
Hill H. H.
Publication year - 1998
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1998.03615995006200030008x
Subject(s) - soil water , chemistry , extraction (chemistry) , organic matter , methanol , supercritical fluid extraction , supercritical fluid , environmental chemistry , soil organic matter , chromatography , organic chemistry , environmental science , soil science
Supercritical fluid extraction (SFE) recoveries of 2,4‐D (2,4‐dichlorophenoxyacetic acid) from spiked Washington soils depended on both pH and organic matter content. The soils used in this study spanned a wide range of organic C concentration (2–480 g kg −1 ). One of the soils (the Benge series A horizon) was adjusted to pHs from 1.8 to 8.3, and extracted with methanol‐modified supercritical CO 2 . Recoveries from this soil increased from 41 to 76% with decreasing pH. For soils at natural pHs, when a weak acid modifier (benzoic acid) was used in addition to methanol, the 2,4‐D recovery ranged from 21 to 86%, increasing with decreasing organic C concentration. Treating the samples to the lowest pHs practical (1.2–1.6) with HCl and extracting with methanol‐modified supercritical CO 2 was more successful than utilizing the weak acid‐methanol modifier, except for the soil with very low organic C. Recoveries after HCl treatment ranged from 80 to 94%. Two soils from 2,4‐D‐treated fields yielded more 2,4‐D by modified SFE at pH 1.2 than by a modified version of the method recommended by the U.S. Environmental Protection Agency. The results suggest that organic acids like 2,4‐D can be successfully extracted at low pH, even from soils high in organic C. Low recoveries from soils high in organic C appear to result from proton consumption by natural soil organic matter during extraction.