Liquid and poly (vinyl chloride) matrix membrane electrodes for the selective determination of cocaine in illicit powders

Abstract

The construction of liquid membrane and PVC matrix-type cocainium ion selective electrodes and their use for direct potentiometry and potentiometric titration of cocaine are described. The ion-pair complexes of cocaine cation with reineckate and tetraphenylborate anions are either dissolved in nitrobenzene solvent or dispersed in a PVC matrix, with DOP or DBS plasticizer, and used as the ion-exchange membranes. The electrochemical response characteristics of electrodes incorporating these types of membranes are evaluated with regard to the effect of pH, foreign basic compounds, temperature and γ-radiation. The electrodes display a stable fast Nernstian response for 10−2-10−5M cocainium cation over the pH range 3–7, the lower limit of detection being 1 μg/ml. Determination of as low as 20 μg/ml cocaine hydrochloride shows an average recovery of 98% and a mean standard deviation of ±0.6%. The electrodes exhibit useful analytical characteristics for determining cocaine in some illicit powders. The results agree fairly well with those obtained by gas-liquid chromatography.