Two-dimensional liquid chromatography–ion trap mass spectrometry for the simultaneous determination of ketorolac enantiomers and paracetamol in human plasma: Application to a pharmacokinetic study

A bioanalytical method was developed for the simultaneous determination of paracetamol and ketorolac enantiomers in human plasma using two-dimensional liquid chromatography–mass spectrometry. Separation was first achieved in a reversed-phase C18 column by using a gradient solvent system consisting of 0.1% aqueous formic acid and acetonitrile (ACN). The effluent between 8.9 and 9.9 min, corresponding to phenacetin and racemic ketorolac peaks, was transferred to a polysaccharide-based chiral column (ChiralPak AD-RH) by using a six-port switching valve. Ketorolac enantiomers were subsequently separated on the chiral column using an isocratic mobile phase composed of ACN/0.1% formic acid 50:50 (v/v). The total run-time was less than 18 min. This innovative strategy prolongs the lifetime of chiral columns by avoiding damages due to the sample matrix. The detection was carried out with an ion trap mass spectrometer equipped with an electrospray ionisation source. The tested ranges were 0.05–20 μg/ml for paracetamol and 0.005–2 μg/ml for each ketorolac enantiomer. This method was fully validated and showed good performances in terms of trueness (80–110%) and precision (6.7–13.2%). The mean extraction recoveries were 60%, 72% and 76% for paracetamol, R-ketorolac and S-ketorolac, respectively. Finally, this procedure was successfully applied to a pharmacokinetic study.