Comparative study of humic substances in soil using pyrolytic techniques and other conventional chromatographic methods

Abstract

Humic acids extracted from an experimental farm soil sample in northern Italy were subjected to analysis of their constituents by pyrolysis–gas chromatography–mass spectrometry (PY–GC–MS) and simultaneous pyrolysis–methylation (SPM). Conventional chromatographic techniques were also used, namely high-performance liquid chromatography for phenolics after nitrobenzene oxidative hydrolysis, and gas chromatography and gas chromatography–mass spectrometry for amino acid analysis after acid hydrolysis and derivatization as trifluoroacetylbutyl derivatives, and fatty acid methyl ester analysis after basic hydrolysis, respectively. Typical chromatographic profiles are presented for phenolic, fatty acid and amino acid analysis. The results are discussed with reference to those obtained by PY–GC–MS and SPM, by means of which 63 and 54 compounds were identified, respectively, corresponding to lignin (phenolics), carbohydrate (furanic and pyranic compounds), lipid (fatty acids) and protein markers. Advantages and problems related to the use of PY–GC–MS and SPM to analyse humic acids are critically evaluated.