Gas chromatographic determination of guanabenz in biological fluids by electron-capture detection

A sensitive gas chromatographic method for the determination of guanabenz[(2,6-dichlorobenzylidene)amino]guanidine in urine and plasma was developed. The method depends upon the acid hydrolysis of guanabenz to 2,6-dichlorobenzaldehyde, which has strong electron capturing properties and is volatile enough to be eluted from a gas chromatographic column. Concentrations as low as 0.1 ng of guana-benz/ml can be determined and recovery of the drug from urine and plasma samples is 81.8+/- 5.5% (SD). No interferences arising from plasma, urine, or reagents were encountered. Examples of the application of the method are given.