Rapid quantification of quinine and its major metabolite (3S)-3-hydroxyquinine in diluted urine by UPLC–MS/MS

A rapid UPLC–MS/MS quantitative assay for the quantification of quinine and (3S)-3-hydroxyquinine requiring minimal sample pre-treatment – dilute-and-shoot type approach – has been developed. The assay was run at 0.6 mL/min using gradient elution with (pH 10; 10 mM) ammonium bicarbonate and methanol with a total cycle time of 2.5 min on a 50 mm × 2.1 mm ID, 1.7 μm Acquity BEH column. Peak shapes were highly symmetrical allowing for accurate peak integration. Calibration curves for both analytes were constructed from 1.00 to 20.00 ng/mL, yielding R2 values >0.995. Intra- and inter-batch assay precision and accuracy were evaluated using 6 injections of QC solutions on 3 separate days (n = 18) and were found to be within ±10% and 90–110% respectively. The method was shown to be suitable for quantitatively determining the ratio of quinine to (3S)-3-hydroxyquinine for a cohort of samples from an epidemiological study.