Selective and sensitive liquid chromatography-tandem mass spectrometry method for the determination of levonorgestrel in human plasma.

A selective, sensitive and rapid liquid chromatography-tandem mass spectrometry method for the determination of levonorgestrel in plasma was developed. An Applied Biosystems API 3000 triple quadrupole mass spectrometer set to multiple reaction monitoring (MRM) mode, using atmospheric pressure photospray ionisation (APPI) in the positive mode. Using 17-alpha-methyltestosterone as internal standard (IS), liquid-liquid extraction was followed by reversed phase liquid chromatography using a phenyl-hexyl column and tandem mass spectrometric detection. The mean recovery for levonorgestrel and 17-alpha-methyltestosterone was 99.5 and 62.9%, respectively. The method was validated from 0.265 to 130 ng levonorgestrel/ml plasma with the lower limit of quantification (LLOQ) set at 0.265 ng/ml. This assay method makes use of the increased sensitivity and selectivity of tandem mass spectrometric (MS/MS) detection, allowing for a rapid (extraction and chromatography) and selective method for the determination of levonorgestrel in human plasma. The assay method was used in a pharmacokinetic study to quantify levonorgestrel in human plasma samples generated after administrating a single oral dose of 1.5 mg levonorgestrel to healthy female volunteers for up to five half lives. The total chromatographic runtime of this method was 5.0 min per sample, allowing for analysis of a large number of samples per batch.