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 0.6mL/min using gradient elution with (pH 10; 10mM) ammonium bicarbonate and methanol with a total cycle time of 2.5min on a 50mm×2.1mm ID, 1.7μm Acquity BEH column. Peak shapes were highly symmetrical allowing for accurate peak integration. Calibration curves for both analytes were constructed from 1.00 to 20.00ng/mL, yielding R(2) 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.