Quantitation of tamsulosin in human plasma by liquid chromatography–electrospray ionization mass spectrometry

A highly sensitive method for quantitation of tamsulosin in human plasma using 1-(2,6-dimethyl-3-hydroxylphenoxy)-2-(3,4-methoxyphenylethylamino)-propane hydrochloride as the internal standard (I.S.) was established using liquid chromatography–electrospray ionization-mass spectrometry (LC–ESI-MS). After alkalization with saturated sodium bicarbonate, plasma were extracted by ethyl acetate and separated by HPLC on a C18 reversed-phase column using a mobile phase of methanol–water–acetic acid–triethylamine (620:380:1.5:1.5, v/v). Analytes were quantitated using positive electrospray ionization in a quadrupole spectrometer. LC–ESI-MS was performed in the selected ion monitoring (SIM) mode using target ions at m/z 228 for tamsulosin and m/z 222 for the I.S. Calibration curves, which were linear over the range 0.2–30 ng/ml, were analyzed contemporaneously with each batch of samples, along with low (0.5 ng/ml), medium (3 ng/ml) and high (30 ng/ml) quality control samples. The intra- and inter-assay variability ranged from 2.14 to 8.87% for the low, medium and high quality control samples. The extraction recovery of tamsulosin from plasma was in the range of 84.2–94.5%. The method has been used successfully to study tamsulosin pharmacokinetics in adult humans.