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Determination of available phenolic compounds in soils by liquid chromatography with solid-phase extraction.

A fast, selective, and sensitive liquid chromatographic (LC) method was developed for determination of derivatives of benzoic and cinnamic acids (gallic, protocatechuic, 2,3,4-trihydroxybenzoic, 4-hydroxybenzoic, vanillic, caffeic, syringic, 4-coumaric, ferulic, sinapic, benzoic, 2-coumaric, cinnamic acids, and 4-hydroxybenzaldehyde and vanillin) in soil samples. The method for sample pretreatment is based on temperature-controlled extraction with water (pH 5.6) for 60 min. Extracts were preconcentrated and purified by solid-phase extraction on OASIS HLB sorbent, with subsequent separation and quantification of individual substances by LC with UV diode-array detection. Limits of detection (3 signal-to-noise LODs) better than 65 ng/g (dry weight) and recoveries from 88 to 99% were found for each compound at absorbance 280 nm. The method was used for determination of bioavailable phenolic compounds in different soil samples.