Quantitative analysis of a novel antimicrobial peptide in rat plasma by ultra performance liquid chromatography-tandem mass spectrometry

We described the first results of a quantitative ultra performance liquid chromatographytandem mass spectrometry method for a novel antimicrobial peptide （phylloseptin, PSN-1）. Chromatographic separation was accomplished on a Waters bridged ethyl hybrid （BEH） C18 （50mm× 2.1 mm, 1.7 μm） column with acetonitrile-water （25：75, v/v） as isocratic mobile phase. Mass spectrometry detection was performed in the positive electrospray ionization mode and by monitoring of the transitions at m/z 679.6/120, 509.6/120 （PSN-1） and m/z 340.7/165 （Thymopentin, IS）. Protein precipitation was investigated and the recovery was satisfactory （above 82%）. The method was shown to be reproducible and reliable with intra-day precision below 5.3%, inter-day precision below 14.2%, and linear range from 0.02 to 2 lag/mL with r〉0.994. The method was successfully applied to a pharmacokinetic study of PSN-1 in rats after intravenous administration.