Enantioselective determination of azelnidipine in human plasma using liquid chromatography–tandem mass spectrometry

A sensitive and simple method was developed for determination of the enantiomers of azelnidipine, (R)-(−)-azelnidipine and (S)-(+)-azelnidipine, in human plasma using chiral liquid chromatography with positive ion atmospheric pressure chemical ionization tandem mass spectrometry. Plasma samples spiked with stable isotope-labeled azelnidipine, [2H6]-azelnidipine, as an internal standard, were processed for analysis using a solid-phase extraction in a 96-well plate format. The azelnidipine enantiomers were separated on a chiral column containing α1-acid glycoprotein as a chiral selector under isocratic mobile phase conditions. Acquisition of mass spectrometric data was performed in multiple reaction monitoring mode, monitoring the transitions from m/z 583 → 167 for (R)-(−)-azelnidipine and (S)-(+)-azelnidipine, and from m/z 589 → 167 for [2H6]-azelnidipine. The standard curve was linear over the studied range (0.05–20 ng/mL), with r2 > 0.997 using weighted (1/x2) quadratic regression, and the chromatographic run time was 5.0 min/injection. The intra- and inter-assay precision (coefficient of variation), calculated from the assay data of the quality control samples, was 1.2–8.2% and 2.4–5.8% for (R)-(−)-azelnidipine and (S)-(+)-azelnidipine, respectively. The accuracy was 101.2–117.0% for (R)-(−)-azelnidipine and 100.0–107.0% for (S)-(+)-azelnidipine. The overall recoveries for (R)-(−)-azelnidipine and (S)-(+)-azelnidipine were 71.4–79.7% and 71.7–84.2%, respectively. The lower limit of quantification for both enantiomers was 0.05 ng/mL using 1.0 mL of plasma. All the analytes showed acceptable short-term, long-term, auto-sampler and stock solution stability. Furthermore, the method described above was used to separately measure the concentrations of the azelnidipine enantiomers in plasma samples collected from healthy subjects who had received a single oral dose of 16 mg of azelnidipine.