COMPARISON OF LIQUID AND GAS-CHROMATOGRAPHY FOR ANALYSIS OF LOW-MOLECULAR-WEIGHT ORGANIC-ACIDS IN RHIZOSPHERE SOIL

Low molecular weight organic acids from rhizosphere soil of durum whea t (Triticum turgidum var. durum L.) were studied by ion exclusion high pressure liquid chromatography (HPLC) and gas chromatography (GC). Io n exclusion HPLC was found unsatisfactory for acid determination becau se poor peak resolution hindered acid identification, strongly ionized solutes and oxalic acid co-eluted in the dead volume of the column, a nd UV detection was not sensitive for aliphatic acid determination. Ex cellent resolution was obtained when the same low molecular weight org anic acids were analyzed by GC. Non-volatile low molecular weight orga nic acids were separated as trimethylsilyl (TMS) derivatives while vol atile acids were analyzed without sample derivatization. A combination of these two GC techniques allowed for separation of 16 acids. Ten lo w molecular weight organic acids were identified and quantified in rhi zosphere soil of durum wheat grown in three different soils. Succinic and acetic acids were most abundant among acids extracted from rhizosp here soils followed by butyric, malic, propionic and tartaric acids. M alonic, fumaric, citric, and trans-aconitic acids were found at the lo west concentrations. Very good resolution, short analysis time, and lo w detection limits make the GC method very suitable for routine determ inations of low molecular organic acids in rhizosphere soil.