Determination of residues of pirimicarb and its desmethyl and desmethylformamido metabolites in fruits and vegetables by liquid chromatography-electrospray/mass spectrometry

A method was developed for the simultaneous determination of residues of pi rimicarb (I) and its desmethylformamido (II) and desmethyl (III) metabolite s in plums, peas, green beans, broad beans, carrots, and swedes. The compou nds were extracted with ethyl acetate and determined, without cleanup, by r eversed-phase liquid chromatography and electrospray mass spectrometry (MS) . MS and MS/MS were used concurrently to monitor the protonated molecules a nd their common collision-induced dissociation product. The limit of detect ion (signal-to-noise ratio of >3) was 1 ng/mL, corresponding to crop concen trations of <0.0015 mg/kg. Ail 3 compounds were determined in plums, broad beans, and green beans by MS without interference. Interferences which affe cted the determination of desmethylformamido-pirimicarb in peas, and to a l esser extent in carrots and swedes, were eliminated by MS/ MS. Recoveries f or all 3 compounds, at 0.05 mg/kg for plums and 0.005 mg/kg for other commo dities, were in the range 83-124%. No interconversion of I, II and III, occ urred during extraction, and the compounds were stable in extracts for grea ter than or equal to 7 days under appropriate conditions.