Determination of imidacloprid, metalaxyl, myclobutanil, propham, and thiabendazole in fruits and vegetables by liquid chromatography–atmospheric pressure chemical ionization–mass spectrometry

Abstract.

Imidacloprid, metalaxyl, myclobutanil, propham, and thiabendazole have been simultaneously determined in strawberries, oranges, potatoes, pears, and melons by matrix solid-phase dispersion (MSPD) followed by liquid chromatography–atmospheric pressure chemical ionization–mass spectrometry (LC–APCI–MS) in positive-ion mode. The samples were homogenized with C₈ bonded silica as MSPD sorbent, placed in a glass column, and eluted with dichloromethane. Chromatographic separation of the compounds was achieved on a reversed-phase LC column using a methanol–ammonium formate (50 mmol L^–1) gradient as a mobile phase. Samples were screened by monitoring the protonated molecular ion at m/z 256 for imidacloprid, 280 for metalaxyl, 289 for myclobutanil, and 202 for thiabendazole, and the main fragment at m/z 138 for propham. Positive samples were confirmed by multiple-ion monitoring. The repeatability (<20%) and recovery (>57%) of the method were good, and limits of detection (<0.05 mg kg^–1) were adequate.