Simultaneous determination of thiabendazole and its major metabolite, 5-hydroxythiabendazole, in bovine tissues using gradient liquid chromatography with thermospray and atmospheric pressure chemical ionisation mass spectrometry.

A novel method is presented for the determination of thiabendazole and 5-hydroxythiabendazole in animal tissues. Samples are homogenised in buffer at pH=7.0, extracted with ethyl acetate and cleaned up using CN solid-phase extraction columns. Thiabendazole and 5-hydroxythiabendazole are separated chromatographically using gradient elution and analysed by liquid chromatography-mass spectrometry. Deuterated thiabendazole is employed as an internal standard for thiabendazole determination; 5-hydroxythiabendazole is quantified via external standards. Samples are screened by monitoring the protonated molecular ions at m/z=202 for thiabendazole, 206 for deuterated thiabendazole and 218 for 5-hydroxythiabendazole using thermospray LC-MS. Positives are confirmed by multiple ion monitoring using APCI LC-MS. Validation of the method was carried out at 50, 100 and 200 microg kg(-1). Recoveries for thiabendazole in bovine muscle, liver and kidney ranged from 96-103% with C.V.s between 0.7 and 4.8% and for 5-hydroxythiabendazole recoveries ranged from 70-85% with C.V.s between 3.1 and 11.5%.