Quantitation of Tricyclic Antidepressant Drugs Based on the Formation of Mixed Aggregates with Surfactants

Abstract

A new approach for the quantitation of drugs, based on the measurement of the critical micelle concentration of mixed surfactant–drug aggregates, is proposed. This methodology involves the photometric titration of drugs in an aqueous medium using a surfactant as titrant. The Coomassie Brilliant Blue G (CBBG) dye, negatively charged, is used as a photometric probe. The analytical applicability of this approach is demonstrated by quantifying tricyclic antidepressants (TCAs) such as imipramine, desimipramine, amitriptylin, and nortriptylin. Aggregates studied included TCA–sodium dodecyl sulfate (SDS) and TCA–Triton X-100 mixtures. Because of the opposite charge of TCAs and SDS, which causes strong synergistic effects in the mixture relative to the properties of their individual components, this anionic surfactant was selected for the quantitation of TCAs. Pharmaceutical preparations can be analyzed directly after dissolution of the samples in water or ethanol. The detection limit achieved for the studied drugs is about 0.12mgL−1, so the proposed method surpasses existing alternative photometric methods in sensitivity and features a detection limit similar to fluorimetric methods. The relative standard deviation for 0.8mgL−1 of TCA is 2.6%.