LC-tandem mass spectrometry method for the simultaneous determination of metformin and sitagliptin in human plasma after ion-pair solid phase extraction

A reversed-phase liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) method was established for simultaneous determination of two oral hypoglycemic drugs metformin (MET) and sitagliptin (STG) in human plasma. The analytes were extracted from 50 mu L human plasma by ion-pair solid phase extraction using sodium lauryl sulphate on PhenomenexStrata-X (30 mg/l mL) cartridges. The chromatographic separation was accomplished on XSelect HSS CN (150 x 4.6mm, 5 mu m) column using mobile phase consisting of methanol-8.0 mM ammonium formate in water, pH 4.5 (80:20, v/v) under isocratic condition. Tandem MS detection was performed on a triple quadrupole spectrometer equipped with an electrospray ionization source, operated in the positive mode. Multiple reaction monitoring (WHIM) was used to quantify the analytes following transitions, m/z 130.1 -> 60.1 and m/z 4083 -> 235.1 for MET and STG respectively. The method displayed acceptable linearity in the concentration range of 4.00-3200 ng/mL for MET and 1.00-800 ng/mL for STG. The intra-batch and inter-batch precisions were <= 5.1% and accuracy ranged from 96.5 to 103.3% for both the drugs. The mean recovery of MET and STG obtained from spiked plasma samples was 82.5% and 90.4% respectively with minimal matrix interference. Both the drugs were found to be stable under all mandatory storage conditions. The validated method was successfully applied to a clinical pharmacokinetic study for a fixed-dose tablet formulation containing 500 mg MET and 50 mg STG in 16 healthy volunteers. (C) 2016 Elsevier B.V. All rights reserved.