Rapid determination of five post-harvest fungicides and metabolite in citrus fruits by liquid chromatography/time-of-flight mass spectrometry with atmospheric pressure photoionization

Liquid chromatography/time-of-flight mass spectrometry (LC/TOF-MS) with atmospheric pressure photoionization (APPI) has been used for the determination of five post-harvest fungicides and metabolite, o-phenylphenol (OPP), diphenyl (DP), thiabendazole (TBZ), imazalil (IMZ), and its major metabolite R14821 (IMZ-M) in citrus fruits. Samples were extracted with diethyl ether and the extracts with minimal sample preparation were analyzed by LC/TOF-MS with APPI by measuring accurate mass. DP, IMZ, and IMZ-M were ionized in positive ion mode, and OPP and TBZ were in negative ion mode. The recoveries fortified to citrus fruits at 1 μg/g ranged from 70.5% to 101.4%. The detection limits (S/N = 3) were 0.002 μg/g (OPP, TBZ, and IMZ-M), 0.001 μg/g (IMZ), and 0.03 μg/g (DP).