Sensitive bioassay for the simultaneous determination of pseudoephedrine and cetirizine in human plasma by liquid-chromatography-ion trap spectrometry.

A liquid chromatography-ion trap mass spectrometry coupled with electrospray ionization (HPLC-ESI-ion trap mass spectrometry) method for simultaneous determination of cetirizine and pseudoephedrine in human plasma is presented. Chromatographic separation was performed on a Hypurity C18 column (Thermo Hypersil-Keystone 2.1 mm x 150 mm, 5 microm, USA), The mobile phase was composed of 65% methanol and 35% water (contained 0.1% formic acid, 10 mM ammonium formate), which was run with a flow-rate of 0.2 ml/min at 40 degrees C. Quantitation was achieved by monitoring the product ions at m/z 166-->m/z 148 (pseudoephedrine), m/z 389.9-->m/z 201.1 (cetirizine), m/z 264-->m/z 246 (tramadol, IS). The calibration curve of pseudoephedrine and cetirizine was established with standard solutions. The limit of detection for pseudoephedrine and cetirizine each was 5 ng/ml. This simplified analytical method is sensitive, specific and accurate enough for simultaneous determination of pseudoephedrine and cetirizine in human plasma and is successfully applied to the pharmacokinetic study of pseudoephedrine and cetirizine.