Determination of the furazolidone metabolite, 3-amino-2-oxazolidinone, in porcine tissues using liquid chromatography-thermospray mass spectrometry and the occurrence of residues in pigs produced in Northern Ireland

A method is presented for the detection of the furazolidone metabolite, 3-amino-2-oxazolidinone (AOZ), in porcine tissue. Bound and extractable residues are detected following methanol-water homogenisation, repeated solvent washing and derivatisation with 2-nitrobenzaldehyde. Samples are analysed by using thermospray mass spectrometry-liquid chromatography, monitoring the positive ion m/z 253 with filament-assisted ionisation. There is no interference from tissue matrices or excess 2-nitrobenzaldehyde reagent. The limit of determination for liver and muscle is 10 ng/g. Recoveries are greater than 80%. The assay was used to investigate the occurrence of furazolidone residues in pigs from Northern Ireland. One hundred samples were analysed. Seventeen of these contained bound AOZ residues. The stability of tissue samples post mortem was investigated in order to achieve optimum storage conditions for samples. When liver was stored at 4 degrees C, the concentration of bound AOZ decreased by 22% within 48 h, However, there were no significant changes in AOZ concentrations in liver that was stored at -20 degrees C for six months.