GAS-CHROMATOGRAPHY OF ALLELOCHEMICALS PRODUCED DURING GLUCOSINOLATE DEGRADATION IN SOIL

Glucosinolate degradation products from Brassica spp. may control soil-borne plant pests; however, a comprehensive method for the analysis of the responsible glucosinolate-derived allelochemicals in soils is lacking. Splitless injection and a 5% phenyl-substituted methylpolysiloxane fused silica capillary column in a gas-liquid chromatograph equipped with a flame ionization detector were used to separate various isothiocyanates, nitriles, and oxazolidinethione in less than 22 min. A linear relationship between detector response for isothiocyanates and molecular weight was observed, allowing estimation of isothiocyanate concentrations for which standards are not readily available. Detection limits for seven of nine compounds were less than 0.1 mu g/mL for 1 mu L injections. The efficacy of various solvents for extraction was examined, as was the effect of salt and extraction time. Quantities of isothiocyanate and nitrile in CH2Cl2 extracts of five soils exceeded 94% of the added spikes, and oxazolidinethione recovery exceeded 84%. Maximum extraction of glucosinolate degradation products from soil amended with crushed seed meal of Brassica napus was obtained in 15 min when 2 mL of 0.20 M CaCl2 was included with the CH(2)CL(2) extractant.