Simultaneous determination of residual tetracyclines in foods by high-performance liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry.

We established a method for precisely determining residual tetracycline antibiotics (TCs) in foods by atmospheric pressure chemical ionization liquid chromatography-tandem mass spectrometry (APCI LC-MS-MS) using selected reaction monitoring with an internal standard. By setting the nebulizer probe temperature to 475 degrees C, we were able to use a mobile phase containing oxalic acid without clogging problems at the APCI interface, since oxalic acid decomposes to carbon dioxide and water at high temperature. DMCTC was very effective as an internal standard for determining TCs in various foods. TCs were cleaned up using a Bond Elut ENV cartridge and analysed by APCI LC-MS-MS. The recovery of TCs from various foods including animal tissues, honey, milk, eggs, and fish fortified at levels of 0.05, 0.10, and 0.50 ppm averaged 60.1-88.9%, with an RSD of 1.2-8.7%. The detection limits were 0.001 ppm for OTC and TC, 0.004 ppm for CTC, and 0.002 ppm for DC. The present method was also successfully used to determine TCs in swine kidney samples that were previously found by microbiological assay.