Rapid analysis of trace levels of antibiotic polyether ionophores in surface water by solid-phase extraction and liquid chromatography with ion trap tandem mass spectrometric detection

The occurrence of antibiotics in surface and ground water is an emerging area of interest due to the potential impacts of these compounds on the environment. This paper details a rapid, sensitive and reliable analytical method for the determination of monensin A and B, salinomycin and narasin A in surface water using solid-phase extraction (SPE) and liquid chromatography-ion trap tandem mass spectrometry (LC-MS-MS) with selected reaction monitoring (SRM). Several product ions as sodiated sodium salts for MS-MS detection have been identified and documented with their proposed fragmentation pathways. Statistical analysis for determination of the method detection limit (MDL), accuracy and precision of the method is described. The average recovery of ionophore antibiotics in pristine and wastewater-influenced water was 96.0 +/- 8.3% and 93.8 +/- 9.1%, respectively. No matrix effect was seen with the surface water. MDL was between 0.03 and 0.05 mug/L for these antibiotic compounds in the surface water. The accuracy and day-to-day variation of method fell within acceptable ranges. The method is applied to evaluate to the occurrence of these compounds in a small watershed in Northern Colorado. The method verified the presence of trace levels of these antibiotics in urban and agricultural land use dominated sections of the river. (C) 2005 Elsevier B.V. All rights reserved.