Analysis of mutagenic heterocyclic amines in cooked beef products by high-performance liquid chromatography in combination with mass spectrometry

Mutagenic activity detected in beef extracts and in fried beef heated for varying periods of time was purified and then analysed by high-performance liquid chromatography in combination with mass spectrometry (LC-MS). The major mutagenic component found in all of the beef products was identified as 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQ_x) followed by lesser amounts of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQ_x). Identification and quantification of mutagens were achieved by the use of deuterium-labelled analogues. Measured levels of MeIQ_x and 4,8-DiMeIQ_x in different batches of beef extract were in the range 11.7-52.2 and 0-11.2 ng/g, respectively, and in beef heated at 275°C for 5-15 min the values of MeIQ_x and 4,8-DiMeIQ_x were in the range 2.7-12.3 and 0-3.9 ng/g, respectively. The levels of IQ found in beef extracts were 0-36.8 ng/g and in fried beef the amounts were estimated at 0.3-1.9 ng/g. The method of purification is rapid, requiring only XAD-2 adsorption followed by an acid-base liquid partition against ethyl acetate and blue cotton treatment (trisulpho-copper-phthalocyanine) prior to LC-MS analysis. Because of the sensitivity of LC-MS, mutagens present in cooked beef can be detected at the low parts-per-billion-level and as little as 10 g of cooked beef was required for analysis.