Preconcentration of tranquilizers by adsorption/extraction at a wax-impregnated graphite electrode

Abstract

The tranquilizers promethiazine, diethazine, trifluoperazine, fluphenazine and clozapin adsorb at the surface and extract into the wax-impregnated graphite electrode (WIGE) as shown by chronocoulometry. Extraction/adsorption at the electrode serves as a preconcentration step which improves the limit of detection for the drugs by differential pulse voltammetry. A 15-min preconcentration gave a linear range of 10 −4–5 × 10 −8 M with a detection limit of 5 × 10 −9 M for clozapin in pH 7 phosphate buffer. The determination of tranquilizers in urine and plasma required no preliminary treatment; the detection limits were 5 × 10 −8 M in urine and 10 −7 in plasma. Plasma measurements were made at a WIGE covered with a Spectrapor membrane to prevent electrode fouling by protein adsorption.