Simultaneous determination of 13 thermo-induced endogenous contaminants in black and green tea based on a split-flow SPE strategy coupled with UPLC-MS/MS analysis.

A rapid and sensitive UPLC-MS/MS method was developed for the simultaneous determination of 13 thermo-induced endogenous contaminants in black and green tea, including acrylamide, 4-methylimidazole, and 11 heterocyclic aromatic amines. To overcome matrix complexity and analyte differences, a two-step extraction combined with a split-flow polymeric cation-exchange (PCX) solid-phase extraction(SPE) procedure was optimised. The method achieved satisfactory linearity (R2 > 0.9988), limits of quantitation (0.005-0.02 mg/kg), and recoveries (71.7%-118.7%) with acceptable intra-day and inter-day RSDs (<19.6%). The validated method was applied to analyse 20 commercial tea samples from China and Japan. The detection rates of 4-methylimidazole, acrylamide, harman, and norharman were 100.0%, 40.0%, 60.0%, and 70.0%, with detected levels ranging from 0.048 mg/kg to 1.449 mg/kg, 0.023 mg/kg to 0.671 mg/kg, 0.005 mg/kg to 0.167 mg/kg, and 0.006 to 0.243 mg/kg. This study provides an effective solution for monitoring multi-class TECs, supporting quality control and safety assurance in tea production.