Gas-liquid chromatography and mass spectrometric ion selective detection of sterigmatocystin in grains

A method was developed for direct gas-liquid chromatographic-mass spectrometric (GLC-MS) analysis of nonderivatized sterigmatocystin in wheat, rice, barley, and corn. Sterigmatocystin was extracted from spiked grain samples by 2 methods, both of which yielded high recoveries of 14C-labeled sterigmatocystin (greater than 90%). Extracts were cleaned up by gel permeation chromatography on polystyrene with tetrahydrofuran as the eluant. Chromatography of 14C-labeled compound indicated good recoveries (greater than 90%). The GLC-MS system was modified to give an all-glass chromatographic pathway to the ion source. Short glass or quartz columns packed with silicone liquid phase on inert supports gave the best results. Trace levels of sterigmatocystin were very labile in all gas chromatographic systems and levels below 5 ppb in grains were detected only with great difficulty. The GLC-MS system was utilized in the mass fragmentography mode, with selective ion monitoring of the m/e 295, 306, and 324 peaks. These ions were present in only trace levels in all control grain samples, indicating minimal interference from other compounds. The limit of accurate detectability (20 ng) on spiked grain samples was lower than previously reported. Lower levels of sterigmatocystin (1 ppb or 4 ng on column) could be detected in grains by using the mass fragmentography mode, but these levels could not be measured accurately.