Rapid method for the determination of metamizole residues in bovine muscle by LC-MS/MS

Metamizole is a pyrazolone non-steroidal anti-inflammatory drug allowed for use in food-producing animals. According to Council Directive 96/23, residues of this drug have to be monitored because of the potential risk to consumers' health. Metamizole is hydrolysed to its marker residue 4-methylaminoantypyrine.This compound is further metabolised to three main metabolites: 4-formylaminoantipyrine, 4-aminoantipyrine and 4-acetylaminoantipyrine. The MRL of 4-methylaminoantipyrine in animal tissues is 100 mu gkg(-1). Considering the above points, a method for the detection of four metamizole metabolites in bovine muscles was developed. Analytes were extracted from muscle by a mixture of acetonitrile and sodium acetate buffer. After centrifugation, the supernatant was passed through alumina cartridges, diluted with mobile phase and analysed by using LC-MS/MS. Four metamizole metabolites were separated on a C8 column in 23min with a gradient of methanol:acetonitrile:ammonium formate solution and analysed by using positive ionisation. Validation of the method indicated a within-laboratory reproducibility in the range of 7-30% and recovery in the range of 45-95%. The method fulfils the criteria for confirmatory methods and, thanks to its labour efficiency, may also be used for screening purposes.