Quantification of the carcinogens 2-amino-3,8-dimethyl- and 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in food using a combined assay based on gas chromatography-negative ion mass spectrometry.

A gas chromatographic-mass spectrometric assay has been developed for the measurement of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in food. Stable isotope-labelled analogues of MeIQx and PhIP are used as internal standards and the synthesis of deuterated PhIP is described. The mass spectrometer is operated in the electron-capture negative ion chemical ionisation mode and the amines are chromatographed as their di-3,5-bistrifluoromethylbenzyl derivatives. All three compounds can be measured in a single chromatographic run and detection limits of 0.05, 0.1 and 0.2 ng/g for MeIQx, DiMeIQx and PhIP, respectively, in food are obtained. Various home-cooked and commercially prepared foodstuffs were analysed with this assay and several were found to contain measurable amounts of one or more of the three amines. These results are presented and discussed.