Determination of spiramycin and tilmicosin in meat and fish by LC/MS

A simple and reliable method using liquid chromatography-electrospray ionization-mass spectrometry (LC/ESI-MS) has been developed for the determination of the macrolide antibiotics spiramycin and tilmicosin in meat and fish. The drugs were extracted from meat and fish with 0.2% metaphosphoric acid-methanol (6:4), and the extracts were cleaned up on an Oasis HLB cartridge (60 mg). Positive ionization produced the molecular related ions, (M + 2H)2+, at m/z 350.2, 422.3 and 435.3 for neospiramycin I, spiramycin I and tilmicosin, respectively. The LC separation was performed on a Capcell Pak MG-C18 column (150 x 2 mm i.d.) with a gradient system of 0.02% formic acid-acetonitrile as the mobile phase at a flow rate of 0.2 mL/min. The molecular-related ions of the drugs were very clear under this condition. The calibration graph for each drug was rectilinear from 0.05 to 5 ng with selected ion monitoring (SIM). The recoveries of the drugs from meat and fish fortified at the level of 0.2 microgram/g was 73.2-89.2%, with high precision. The limits of detection of the drugs in meat and fish were 0.01 microgram/g.