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 o f the responsible glucosinolate-derived allelochemicals in soils is la cking. Splitless injection and a 5% phenyl-substituted methylpolysilox ane fused silica capillary column in a gas-liquid chromatograph equipp ed with a flame ionization detector were used to separate various isot hiocyanates, nitriles, and oxazolidinethione in less than 22 min. A li near relationship between detector response for isothiocyanates and mo lecular weight was observed, allowing estimation of isothiocyanate con centrations for which standards are not readily available. Detection l imits 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 exam ined, as was the effect of salt and extraction time. Quantities of iso thiocyanate and nitrile in CH2Cl2 extracts of five soils exceeded 94% of the added spikes, and oxazolidinethione recovery exceeded 84%. Maxi mum 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.