[LC-MS/MS method for simultaneous quantification of lopinavir and ritonavir in human plasma]

A liquid chromatographic-tandem mass spectrometric (LC-MS/MS) method was developed for the determination of lopinavir and ritonavir in human plasma. Analytes were separated from plasma by a combination of alkalinized protein precipitation and liquid-liquid extraction with ethyl acetate. Chromatographic separation was performed on a Agilent ZORBAX Eclipse XDB-C18 column with the mobile phase consisted of methanol-0.1% formic acid in water (80:20). A tandem mass spectrometer equipped with electrospray ionization source was used as detector and operated in the positive ion mode. Quantification was performed using multiple reaction monitoring (MRM) of the transitions m/z 629.6 --> 155.2, m/z 721.4 --> 268.2, and m/z 515.2 --> 276.2 for lopinavir, ritonavir and telmisartan (internal standard), respectively. The method showed a good linearity in a concentration range of 62.5 - 10000 ng mL(-1) for lopinavir, and 12.5 - 2000 ng mL(-1) for ritonavir. The lower limits of quantification were 15 pg mL(-1) and 8 pg mL(-1) for lopinavir and ritonavir, respectively. The intra- and inter-day precision was less than 15% and the absolute recovery was above 75%. This method was selective and rapid, sensitive for investigating blood drug concentrations in clinics.