Analysis of tricyclic antidepressants in pharmaceuticals by microemulsion liquid chromatography

Basic compounds yield long retention times and broad and asymmetric peaks in reversed-phase liquid chromatography, due to interaction with residual silanols in the columns. The addition of the surfactant sodium dodecyl sulphate in the so called micellar liquid chromatography enhances the efficiency, but long retention is achieved, due to electrostatic interaction between the cationic species of basic compounds and the anionic sulphate group of the surfactant. This forces the addition of a strong organic solvent to get appropriate times. An alternative is the use of a microemulsion (ME), formed by mixing surfactant, oil and an alcohol as co-surfactant. Association of hydrophobic compounds with the oil droplets increases the elution strength, which is translated in short retention. The advantages of using MEs in the analysis of tricyclic antidepressants, compared to the use of hydro-organic mixtures and micellar mobile phases, are here studied. A method with an ME containing 0.173 M SDS, 1.42% (v/v) octane and 8.15% (v/v) 1-butanol was developed and validated for the analysis of amitryptiline, clomipramine, imipramine, maprotiline and nortryptiline in pharmaceutical formulations. Satisfactory results were obtained, with intraand inter-day precisions below 2.5%, and intraand inter-day accuracy between-1.7% and 1.2%. Good recoveries were obtained with a simple sample preparation.

Automated summary

Basic compounds in reversed-phase liquid chromatography interact with residual silanols in the columns, resulting in long retention times and broad peaks. The addition of surfactant sodium dodecyl sulphate enhances efficiency, but requires the use of strong organic solvents. Alternatively, microemulsions can increase elution strength and shorten retention times.