Liquid chromatographic determination of irbesartan in human plasma

A simple and sensitive method was developed for determination of irbesartan by liquid chromatography with fluorescence detection. Irbesartan and losartan (I.S.) in human plasma were extracted using diethyl ether:dichloromethane (7:3, v/v) followed by back extraction with 0.05 M sodium hydroxide. Neutralized samples were analyzed using 0.01 M potassium dihydrogen phosphate buffer (containing 0.07% triethylamine as peak modifier, pH was adjusted with orthophosphoric acid to pH 3.0) and acetonitrile (66:34, v/v). Chromatographic separation was achieved on an ODS-C-18 column (100 mm × 4.6 mm i.d., particle size 5 μm) using isocratic elution (at flow rate 1.25 ml/min). The peak was detected using a fluorescence detector set at Ex 259 nm and Em 385 nm, and the total time for a chromatographic separation was ∼13 min. The validated quantitation ranges of this method were 15–4000 ng/ml with coefficients of variation between 0.75 and 12.53%. Mean recoveries were 73.3–77.1% with coefficients of variation of 3.7–6.3%. The between- and within-batch precision were 0.4–2.2% and 0.9–6.2%, respectively. The between- and within-batch relative errors (bias) were (−5.5) to 0.9% and (−0.6) to 6.9%, respectively. Stability of irbesartan in plasma was >89%, with no evidence of degradation during sample processing and 60 days storage in a deep freezer at −70 °C. This validated method is sensitive and simple with between-batch precision of <3% and can be used for pharmacokinetic studies.