Quantitation of Sirolimus in Human Whole Blood by Ultra Performance Liquid Chromatography Tandem Mass Spectrometry for a Bioequivalence Study

A sensitive and high throughput ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method has been developed for the determination of sirolimus in human whole blood. The method involved protein precipitation with ZnSO4, followed by solid phase extraction of sirolimus along with tacrolimus as the internal standard (IS) from 100 μL of human blood. The chromatographic analysis was achieved on a Waters Acquity UPLC BEH C18 (50 mm × 2.1 mm, 1.7 μm) analytical column using gradient mobile phase, consisting of 10 mM ammonium acetate, pH 5.00 adjusted with acetic acid and premixed methanol and acetonitrile (60:40, v/v), at a flow-rate of 0.400 mL/min. The precursor → product ion transition for sirolimus (m/z 931.6 → 864.4), and IS (m/z 821.5 → 768.3) were monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring and positive ionization mode. The method is validated over a wide dynamic concentration range of 0.05-50.0 ng/mL. Matrix effect is assessed by post-column analyte infusion experiment and the mean extraction recovery was greater than 93.0 % for sirolimus and IS. The method is rugged and rapid with a total run time of 1.5 min and was used in a clinical study with 16 healthy subjects. The assay reproducibility was successfully demonstrated by reanalysis of 87 subject samples.