“…Selective elution with water: methanol: acetonitrile (2: 3: 3) allowed differentiation from tricyclic antidepressants, which could be later eluted with 0·6% diethylamine in rnethanol.l" Casas et al 219 extracted seven benzodiazepines from urine and plasma using a variety of solid phase materials. They found C2 columns to be superior to C 18, C 12 and C8 columns with 90'Yo extraction and little endogenous interference, although Gaillard et al 220 obtained similar results using C8 columns eluting with 0·5% acetic acid in methanol. Where other drugs are also present, a mixed bed column may be preferable.P' Extraction using Sep-pak C-18 cartridges (Waters Corporation, Milford, MA, USA) as a preliminary to capillary GC is less effective for plasma than for urine."!"…”