title: Streamlining methodology for the multiresidue analysis of beta-lactam antibiotics in bovine kidney using liquid chromatography-tandem mass spectrometry.
abstract: A previously reported multiresidue method for the analysis of 11 important beta-lactams (amoxicillin, ampicillin, cefazolin, cephalexin, cloxacillin, desfuroylceftiofur cysteine disulfide (DCCD), deacetylcephapirin, dicloxacillin, nafcillin, oxacillin, and penicillin G) in bovine kidney has been further streamlined. The method is based on a simple extraction using acetonitrile-water (4:1, v/v), followed by dispersive solid-phase extraction clean-up with C(18) sorbent, concentration of an extract aliquot, and filtration of the final extracts using syringeless filter vials, which are used for the sample introduction in the liquid chromatographic-tandem mass spectrometric (LC-MS/MS) analysis. The recoveries have been improved by adding the internal standard [(13)C(6)]sulfamethazine to the homogenized sample before the extraction step, which enabled a proper control of the volume changes during the sample preparation. Average recoveries of fortified samples were 87-103% for all beta-lactams, except for DCCD, which had an average recovery of 60%. Based on the results of the stability study and LC mobile phase tests, methanol has been eliminated from the entire method, including the LC-MS/MS analysis. The best overall LC-MS/MS (electrospray positive ionization) performance was achieved by using 0.1% formic acid as an additive in both parts of the mobile phase, in water and in acetonitrile. To prevent carry-over in the LC-MS/MS analysis, the LC method was divided into two parts: one serving as an analytical method for injection of the sample and elution of the analytes and the other one, starting at a highly organic mobile phase composition, being dedicated for injection of a solvent, washing of the system, and equilibration of the column to the initial conditions of the analytical method. In this way, a blank solvent is injected after each sample, but these in-between injections contribute minimally to the overall sample throughput.
authors.affiliation: US Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA 19038, USA. katerina.mastovska@ars.usda.gov
authors.forename: Katerina
authors.initials: K
authors.lastname: Mastovska
authors.forename: Alan R
authors.initials: AR
authors.lastname: Lightfield
mesh_terms: D000658:Amoxicillin / Q000032:analysis; D000667:Ampicillin / Q000032:analysis; D000818:Animals; D000900:Anti-Bacterial Agents / Q000032:analysis*; D002417:Cattle; D002511:Cephalosporins / Q000032:analysis; D002853:Chromatography, Liquid / Q000379:methods*; D003023:Cloxacillin / Q000032:analysis; D007668:Kidney / Q000737:chemistry*; D010406:Penicillins / Q000032:analysis; D015203:Reproducibility of Results; D053719:Tandem Mass Spectrometry / Q000379:methods*; D047090:beta-Lactams / Q000032:analysis*
chemical_list: D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D010406:Penicillins; D047090:beta-Lactams; C063324:desfuroylceftiofur; D000667:Ampicillin; D000658:Amoxicillin; D003023:Cloxacillin