Response surface methodology for the optimisation of flow-injection analysis with in situ solvent extraction and fluorimetric assay of tricyclic antidepressants

A semiautomatic extraction-fluorimetric method for the determination of tricyclic antidepressant drugs (TCAs) based in the formation of ion pairs with 9,10-dimethoxyanthracene-2-sulphonate (DMAS) has been developed. The aqueous solutions of the TCAs (imipramine, desipramine, amitriptyline, nortriptyline, clomipramine or doxepine) are injected into a carrier composed by DMAS in an acid medium and the ion pair formed is extracted into dichloromethane where the fluorescence is measured. An experimental design (Central Composite Design) together with the Response Surface Methodology has been used to find the optimal instrumental FIA and chemical variables. We have considered as the response function the product of the peak height by the sampling frequency. The calibration curves were linear over the working range (0.25-3.00 mg L⁻¹). The limits of detection were lower than 0.30 mg L⁻¹. The method has been satisfactorily applied to the determination of imipramine, amitriptyline, clomipramine and doxepin in pharmaceutical preparations.