Rapid determination of tafenoquine in small volume human plasma samples by high-performance liquid chromatography–tandem mass spectrometry

A method was developed for the determination of tafenoquine (I) in human plasma using high-performance liquid chromatography–tandem mass spectrometry. Prior to analysis, the protein in plasma samples was precipitated with methanol containing [2H315N]tafenoquine (II) to act as an internal standard. The supernatant was injected onto a Genesis-C18 column without any further clean-up. The mass spectrometer was operated in the positive ion mode, employing a heat assisted nebulisation, electrospray interface. Ions were detected in multiple reaction monitoring mode. The assay required 50 μl of plasma and was precise and accurate within the range 2 to 500 ng/ml. The average within-run and between-run relative standard deviations were <7% at 2 ng/ml and greater concentrations. The average accuracy of validation standards was generally within ±4% of the nominal concentration. There was no evidence of instability of I in human plasma following three complete freeze–thaw cycles and samples can safely be stored for at least 8 months at approximately −70°C. The method was very robust and has been successfully applied to the analysis of clinical samples from patients and healthy volunteers dosed with I.