Determination of clonidine in human plasma by cold on-column injection capillary gas chromatography-selected-ion monitoring-mass spectrometry.

Clonidine [Catapres, 2-(2,6-dichlorophenylimino)-2-imidazoline hydrochloride], a potent, antihypertensive drug, given in a dosage of 0.1-0.3 mg, yields plasma levels in the ng/ml to pg/ml range. A method for the determination of clonidine from human plasma was developed, which includes a simple, one-step solvent extraction followed by a one-step derivatization with N-methyl-N-(tert.-butyldimethylsilyl)trifluoroacetamide to form a tert.-butyldimethylsilyl (TBDMS) derivative. Levels of clonidine (TBDMS) were determined by cold on-column injection capillary gas chromatography-selected-ion monitoring-mass spectrometry. Precision of the method at the 1 ng/ml level was +/- 2.4%.