Detection and measurement of MeIQx in human urine after ingestion of a cooked meat meal.

A gas chromatographic-mass spectrometric assay has been developed for the measurement of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) in urine. The method employs capillary column gas chromatography, electron capture negative-ion chemical ionization mass spectrometry, a stable isotope-labelled analogue of MeIQx as internal standard and has a limit of detection of 5 pg MeIQx/ml urine. Six subjects consumed a fried beef meal and urine was collected before and after this event. While no MeIQx could be detected in urine collections made prior to meat consumption, the 12-h urine collections of all six subjects made after the meal contained the amine. When the amounts of MeIQx measured in the urine collections were compared to the quantities of amine ingested in the fried beef, it was found that 1.8-4.9% of the oral dose was excreted unchanged in urine. Metabolic studies in animals lead us to believe that MeIQx in the diet is efficiently absorbed and extensively biotransformed.