A rapid and sensitive liquid chromatography-tandem mass spectrometry method was developed and validated to quantify levonorgestrel in human plasma.After liquid-liquid extraction with ethyl acetate,the analytes were separated on a Phenomenex Luna C18 column interfaced with a tripe-quadrupole tandem mass spectrometer using positive electrospray ionization.Norethindrone was used as the internal standard.The standard calibration curve was linear over the concentration range 0.625-40 ng·mL-1.The intra-day and inter-day precisions were less than 8.16% from the determination of QC samples.Accuracy was within ±7.3%.The method was successfully applied for pharmacokinetic study of levonorgestrel after oral administration of 1.5 mg levonorgestrel to 20 healthy volunteers.
