Adsorption of drugs in high-performance liquid chromatography injector loops

The effect of solvent injection on the area and peak-height responses of some drugs (ergotamine tartrate, astemizole, terfenadine, bromhexine hydrochloride, caffeine, ambroxol hydrochloride, phenylephrine hydrochloride, enalapril maleate and betamethasone) was evaluated. Reversed-phase chromatographic systems were employed and loops of different sizes and various overfill volumes were assayed. When injection solvents weaker than the mobile phases were used, significant variation in the area responses was observed for astemizole, bromhexine, ergotamine and terfenadine. Adsorption on the internal surface of the injection loops produced this anomalous behaviour depending on the chemical nature of the analyte injected.