Liquid chromatographic–mass spectrometric determination of post-harvest fungicides in citrus fruits

Liquid chromatography (LC)–atmospheric pressure ionisation (API)–mass spectrometry (MS) has been used to determine residues of five fungicides in oranges with a minimum sample cleanup. Atmospheric pressure chemical ionisation (APCI) and electrospray (ES) were compared and both gave similar results in terms of sensitivity and structural information. The main ions were [M+H]+for carbendazim, imazalil, thiophanate methyl and thiabendazole, and [M+H–C4H9NHCO]+ for benomyl. Samples were extracted with sodium sulphate and ethyl acetate. Although benomyl and thiophanate methyl were transformed through the extraction procedure to carbendazim, the method showed good precision (<13%) and recovery (>70%), except for thiophanate methyl (50%), whilst also yielding limits of detection (<0.03 mg kg−1) that are adequate for the determination of the studied fungicides in oranges.