Alkylated cyclodextrin-based potentiometric and amperometric electrodes applied to the measurement of tricyclic antidepressants

Alkylated alpha, beta and gamma cyclodextrins have been incorporated in ion-selective electrodes as neutral ionophores and used for the detection of the tricyclic antidepressants imipramine, desipramine and trimipramine as their hydrochloride salts. Nernstian response and excellent potentiometric limits of detection were observed with each of the three alkylated cyclodextrins examined. Interference from 'serum' levels of Na+, K+ and Ca2+ ions was very low. Interference from organic molecules such as glycine, L-histidine and nicotinamide was also low in most cases (see text for exceptions). Electrodes suitable for amperometric measurements were assembled by depositing alkylated cyclodextrins on screen printed electrode substrates. Inclusion of the tricyclic antidepressants in the cyclodextrin cavity aided by controlled potential electrolysis, allowed subnanomolar levels of the analyte to be monitored by square wave voltammetry. Mechanistic studies indicated that, by preconditioning the modified electrodes at approximately +0.6 V in phosphate buffer, the appropriate radical cation was formed, which, on further conditioning at approximately -0.2 V rapidly formed the dimer which possessed a lower oxidation potential of approximately +0.18 V. Monitoring the redox wave at 0.18 V afforded a powerful analytical handle for trace analysis of these tricyclic antidepressants. This redox wave is observable only in the presence of aqueous phosphate which may be attributed to the formation of a hydrogen-bonded surface ion-pair including the substrate and a phosphate counterion.