Simultaneous determination of nicotinic acid and its metabolites using hydrophilic interaction chromatography with tandem mass spectrometry.

A hydrophilic interaction chromatographic (HILIC) system interfaced with atmospheric pressure ionization (API) sources and a tandem mass spectrometer (MS/MS) was developed for the simultaneous determination of nicotinic acid (NiAc) and its metabolites in dog plasma in support of a pharmacokinetic study. A silica column was adapted for separation of NiAc and its two metabolites, nicotinamide (NiNH2) and nicotinuric acid (NiUAc), under HILIC conditions. The influence of experimental factors such as the composition of mobile phase on ionization efficiency and chromatographic performance of all analytes was investigated. The feasibility of the proposed HILIC/MS/MS methods was explored by comparing the plasma levels of NiAc, NiNH2, and NiUAc in dog obtained by using either electrospray ionization or atmospheric pressure chemical ionization interfaces in positive ion mode. The methods were partially validated in terms of inter-day accuracy and precision, extraction recovery, benchtop and freeze/thaw stability. Further, the potential of ionization suppression resulting from endogenous components of the biological matrixes on the HILIC/API-MS/MS methods were investigated using the post-column infusion technique.