Ultratrace analysis of nine macrolides, including tulathromycin A (Draxxin), in edible animal tissues with minicolumn liquid chromatography tandem mass spectrometry

The analysis of nine macrolides is presented, including tulathromycin A (Draxxin), in beet, poultry, and pork muscle with a simple multiresidue extraction and analysis method using high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry. The sample preparation method involves extraction with acetonitrile and defatting with hexane followed by dilution of the extracts for analysis. Separation of the nine macrolides was performed using an Atlantis dC(18), 3 mu m, 3.9 mm x 20 mm minicolumn (guard column). Detection was carried out with two multiple reaction monitoring experiments per macrolide. The method detection limits (MDLs) were based on three times standard deviation of eight repeat spikes at 3.0 ng/g of a mix of the nine macrolides in the various tissues. The MDLs and retention times for the macrolides were as follows: lincomycin, 0.19 ng/g (t(R) = 5.00 min); tulathromycin, 0.46 ng/g (t(R) = 5.63 min); spiramycin, 0.21 ng/g (t(R) = 6.06 min); pirlimycin, 0.10 ng/g (t(R) = 6.04 min); clindamycin, 0.16 ng/g (t(R) = 6.20 min); tilmicosin, 0.29 ng/g (t(R) = 6.38 min); erythromycin, 0. 19 ng/g (t(R) = 6.62 min); tylosin, 0. 10 ng/g (t(R) = 6.72 min); and josamycin, 0.09 ng/g (t(R) = 6.98 min). Precision at 25 ng/g (n = 4) ranged from 2.3 to 9.4% for the compounds from beef muscle. Of interest is the detection of incurred residues of tulathromycin A in edible calf tissue at 0.10-7 mu g/g, which is presented here for the first time.