Assay of colistin A, B and colistin methanesulfonate in human plasma by LC-MS/MS and short-term plasma stability

A simple liquid chromatography tandem mass spectrometry (LC-MS/MS) assay for the determination of colistin A and colistin B in human plasma was developed and validated.Plasma extraction was performed using Oasis HLB 1 ml cartridges, analysis was performed using Arion® Polar C18 (250 × 4,6 mm; 5 mm) column at 35 °C.Mobile phases consisted of water containing 0,1% formic acid and methanol containing 0,1% formic acid (40 : 60, v/v) delivered at a flow rate of 0,8 ml/minute.Eluent was detected in the positive ion mode using electrospray ionization at the following transitions of mass to charge (m/z): colistin A 585, 55 → 101,05; colistin B 578,5 → 101,15; and IS 602,4 → 101,1; 120,15; 86,15.Short-term stability tests of colistin and CMS were performed, at room temperature and 37 °C, where the stability of both components decreases with increasing temperature.The presented paper is part of the Pharmacokinetics of Colistin in Critically Ill Patients With Extracorporeal Membrane Oxygenation (COL-ECMO2022) study in which further results will be presented.