Precolumn o-Phthalaldehyde-N-acetyl-L-cysteine Derivatization Followed by RP-HPLC Separation and Fluorescence Detection of Sitagliptin Enantiomers in Rat Plasma

An indirect reversed-phase high-performance liquid chromatographic separation and fluorescence detection of sitagliptin enantiomers in rat plasma was developed and validated. Deproteinized rat plasma containing racemic sitagliptin was derivatized with o-phthalaldehyde and N-acetyl-L-cysteine under alkaline conditions, converted to diastereomers, and separated on a Lichrospher 100 RP-18e column using 20 mM phosphate buffer and methanol (45:55 v/v) as a mobile phase under isocratic mode of elution at a flow rate of 1.0 mL/min. Fluorescence detection was performed at 330 and 450 nm as excitation and emission wavelengths, respectively. The method was linear in the range of 50–5000 ng/ mL for both enantiomers. The intra- and interday accuracy and precision were within the predefined limits of ≤15% at all concentrations. The method was successfully applied to a pharmacokinetic study of sitagliptin after 5 mg/kg oral administration to Wistar rats. Robustness of the method was evaluated using design of experiments. Chirality 25:883–889, 2013. © 2013 Wiley Periodicals, Inc.