Determination of guanfacine in human plasma by GC-MS with electron capture negative chemical ionization.

Abstract Electron capture negative chemical ionization mass spectrometry has been applied to the determination of guanfacine in biological samples. After derivatization with hexafluoroacetylacetone, gas-chromatography on fused silica capillary column and negative chemical ionization with methane, the compound is quantified using selected ion monitoring by comparing the intensity of the molecular anion at m/z = 417 with the intensity of the corresponding anion from the stable isotope labelled ( 13 C- 15 N 3 -guanfacine) as internal standard. This method has been applied to the determination of the pharmacokinetic profile of guanfacine in man after a 2 mg oral dose.