A simple and sensitive high-performance liquid chromatography mass spectrometry（LC-MS）method for the simultaneous determination of irbesartan and hydrochlorothiazide in human plasma was developed and applied to a pharmacokinetic study. Acetaminophen was used as the internal standard（IS）.Sample pretreatment using liquid-liquid extraction with ethyl acetate was used.The analysis was carried out on an Elite SinoChrom ODS-BP C_（18）column with a mobile phase composed of acetonitrile-water （35：65,v/v）.Target ions were [M-H]^-m/z 427.25 for irbesartan,[M-H]^-m/z 295.95 for hydrochlorothiazide and [M-H]^- m/z 150.05 for the IS via an electrospray ionization（ESI）source.The intra-and inter-day precision（RSD%）was below 14.5% for irbesartan and hydrochlorothiazide,and the accuracy（RE%）was less than 1.9% and-2.0% for irbesartan and hydrochlorothiazide,respectively.The linear calibration curves were obtained in the concentration range of 10-5000 ng/mL （r0.99）for irbesartan and 1-200 ng/mL（r0.99）for hydrochlorothiazide with the lower limit of quantification（LLOQ）of 10 ng/mL and 1 ng/mL,respectively.The method was applied to a clinical pharmacokinetic study of a tablet containing irbesartan and hydrochlorothiazide in healthy Chinese volunteers after oral administration.
A rapid and sensitive high performance liquid chromatography-mass spectrometry （HPLC-MS） method for the quantification of nimesulide in human plasma was developed and validated. Sample aliquots of 100μL were extracted by one-step liquid-liquid extraction after addition of hydrochlorothiazide as the internal standard （IS）. Analytes were separated on a reverse phase C18 column using methanol-water （84：16, v/v） as the mobile phase and detected by a single quadrupole mass spectrometer in selected ion monitoring （SIM） negative mode. Monitored m/z values for nimesulide and IS were 307.00 and 295.90, respectively. The overall run time was 4.2 min. Validation experiments demonstrated good precision and accuracy over a wide concentration range of 20.0-7000 ng/mL with a lower limit of quantification （LLOQ） at 20.0 ng/mL. No interference by endogenous substances or matrix effect was observed. Average extraction recoveries for nimesulide and IS were all greater than 84.4%. The assay was successfully applied to a bioequivalence study of nimesulide dispersible tablets in Chinese male volunteers after oral administration.
A sensitive RP-HPLC-UV method has been developed and validated for the quantification of daphnoretin in rat plasma. Daphnoretin was extracted from rat plasma by protein precipitation and liquid-liquid extraction. Separation was performed on a Diamonsil C18 column （200 mm× 4.6 mm, 5 μm） with a mobile phase of methanol-20 mmol/L ammonium acetate （adjusted to pH 3.2 with acetic acid, 42：58, v/v） at a flow rate of 1.0 mL/min. The UV detector was set at 345 nm and column temperature was set at 40 ℃. The calibration curves were linear over the concentration range of 0.020-2.00 ~tg/mL, The lower limit of quantification （LLOQ） of daphnoretin in rat plasma was 0.020 μg/mL. The intra- and inter-day relative standard deviation （RSD） for measurement of quality control （QC） samples （0.050, 0.200 and 1.60 μg/mL） ranged from 5.0%-10.6%. Relative error （RE） was from ±（1.2%-2.5%）. The validated method was used successfully in a pharmacokinetic study of daphnoretin in rats after intraperitoneal injection.
