Abstract: A rapid and effective method was developed for the simultaneous determination of Nε-carboxymethyllysine (CML) and Nε-carboxyethyllysine (CEL) in thermally processed foods by ultra-high performance liquid chromatography-triple quadrupole-tandem mass spectrometry (UPLC-QqQ-MS/MS). After the defatted samples were reduced by sodium borohydride for 8 h, the protein was precipitated with a mixed solvent of chloroform and methanol (2:1, V/V) and then hydrolyzed with hydrochloric acid. Subsequently, CML and CEL were concentrated and purified on an Oasis MCX SPE column, and separated on ACQUITY UPLC HSS T3-C18 analytical column with gradient elution using a mobile phase consisting of 1 mmol/L aqueous ammonium acetate containing 0.1% formic acid and acetonitrile. The qualitative and quantitative analysis was performed in the positive ionization mode with multiple reaction monitoring (MRM). The results showed that the developed method had a good linear relationship in the concentration of 0.25–500 ng/mL with a correlation coefficient of over 0.999. The limit of detection (LOD) was 8 and 10 ng/g , and the limit of quantitation (LOQ) was 36 and 40 ng/g for CML and CEL, respectively. The average recoveries of CML and CEL at three spiked concentration levels were 96%–103% and 94%–107%, respectively, and the precision, expressed by relative standard deviations (RSD), was 1.48%–2.43% and 1.23%–1.84%, respectively. CML and CEL contents in 13 commercially available thermally processed foods were detected by this method. It was found that the contents of CML and CEL in infant meat floss and biscuits were significantly higher than those in baked and fried foods (P < 0.05). The results indicate that the method established in this study is rapid, precise, and effective for the simultaneous determination of CML and CEL in thermally processed foods.

Key words: ultra-high performance liquid chromatography-quadrupole-tandem mass spectrometry; thermally processed foods; Nε-carboxymethyllysine; Nε-carboxyethyllysine