DETERMINATION OF TEBUTHIURON AND METABOLITES IN BOVINE-MILK BY GC-MSD

A method is described for the determination of tebuthiuron and five metabolites [metabolite 104, N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N-methylurea; metabolite 106, N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-y1] urea; metabolite 109, N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N'- (hydroxymethyl)-N-methylurea; metabolite 104(OH), N-[5-(2-hydroxy-1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl] -N-methylurea; and metabolite 109(OH), N-[5-(2-hydroxy-1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N' -(hydroxymethyl)-N-methylurea] in bovine milk. The compounds are extracted from acid-hydrolyzed milk with ethyl acetate or methyl tert-butyl ether, and samples are purified with alumina and C-18 solid phase extractions. Following trifluoroacetylation and silylation, the analytes are quantitated by gas chromatography with mass spectrometric detection in the selected ion monitoring mode. During hydrolysis, metabolites 109 and 109(OH) are converted to 104 and 104(OH), respectively; therefore, quantitation of metabolites 104 and 104(OH) includes these two metabolites as well. Additional purification and derivatization steps are required for the isolation and determination of metabolite 106, thus necessitating separate analysis. Limits of quantitation for all of the analytes range from 0.02 to 0.09 mu g/mL.