Comparison of liquid and gas chromatography for analysis of low molecular weight organic acids in rhizosphere soil

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Abstract
Low molecular weight organic acids from rhizosphere soil of durum wheat (Triticum turgidum var. durum L.) were studied by ion exclusion high pressure liquid chromatography (HPLC) and gas chromatography (GC). Ion exclusion HPLC was found unsatisfactory for acid determination because poor peak resolution hindered acid identification, strongly ionized solutes and oxalic acid co‐eluted in the dead volume of the column, and UV detection was not sensitive for aliphatic acid determination. Excellent resolution was obtained when the same low molecular weight organic acids were analyzed by GC. Non‐volatile low molecular weight organic acids were separated as trimethylsilyl (TMS) derivatives while volatile acids were analyzed without sample derivatization. A combination of these two GC techniques allowed for separation of 16 acids. Ten low molecular weight organic acids were identified and quantified in rhizosphere soil of durum wheat grown in three different soils. Succinic and acetic acids were most abundant among acids extracted from rhizosphere soils followed by butyric, malic, propionic and tartaric acids. Malonic, fumaric, citric, and trans‐aconitic acids were found at the lowest concentrations. Very good resolution, short analysis time, and low detection limits make the GC method very suitable for routine determinations of low molecular organic acids in rhizosphere soil.