Rapid and reliable identification of ionophore antibiotics in feeds by liquid chromatography-tandem mass spectrometry.

Veterinary diagnostic laboratories are constantly required to be innovative to develop quick, reliable, and cost-effective methods for use in diagnosis of intoxications. Livestock intoxication with ionophore antibiotics is sometimes encountered. A rapid qualitative method based on liquid chromatography-tandem mass spectrometry was developed to screen for the presence of monensin, lasalocid, salinomycin, and narasin antibiotics in feeds. This new method has high specificity and high sensitivity, and yet minimum sample preparation was employed. The analytes were extracted in methanol-water (9010) and analyzed without further purification. Because the test uses a single extraction procedure and no cleanup is necessary, its turnaround time is 4 hr. The method applies the concept of "identification points" (IP) score to identify suspected ionophore antibiotics. The total IP score used to identify each of the ionophore antibiotics by this method was 7.0, which exceeds the minimum score of 4.0 required for acceptable identification of unknown compounds. The specificity of the method was achieved using retention time and multiple reaction monitoring with a total IP score of 7.0.