A determinative and confirmatory method for residues of the metabolites of carbadox and olaquindox in porcine tissues

Carbadox (CBX) and olaquindox (OLQ) are used in swine feed for growth promotion, to improve feed efficiency, increase the rate of weight gain, control swine dysentery and bacterial enteritis in young swine. In 1991, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) recommended maximum residue limits (MRLs) of 30 and 5 μg kg−1 in liver and muscle tissues of pigs, respectively, based on the concentration of, and expressed as, quinoxaline-2-carboxylic acid (QCA) as marker residue. In 1998, the European Commission (EC) banned the use of CBX and OLQ in food animal production together with four other feed additives, following reports that CBX and desoxycarbadox (DCBX) are suspect carcinogens and mutagens. In 2001, the sale of CBX was halted in Canada. In 2003, JECFA recommended the withdrawal of the previously recommended acceptable daily intake (ADI) and MRLs and concluded that QCA was not a suitable marker residue for CBX, based on new sponsor studies reporting that DCBX, the suspect carcinogen, persisted in animal tissues much longer than had previously been thought. This paper presents a very sensitive LC–MS/MS method that was developed by CFIA scientists for the simultaneous determination and confirmation of DCBX residues at concentrations ≥0.050 ng kg−1 and QCA and mQCA residues at concentrations ≥0.50 ng kg−1in bovine muscle, pork liver and muscle tissues.