Poly(vinyl chloride) matrix membrane electrode for the selective determination of heroin (diamorphine) in illicit powders

The potentiometric response characteristics of a poly(vinyl chloride) membrane electrode for heroin based on its ion-pair complex with tetraphenylborate were examined. The influence of pH, temperature and time on the performance of the electrode system was investigated. The electrode shows a near-Nernstian response over the heroin concentration range 10(-2)-10(-4) M with good precision. The mean relative standard deviation for the determination of heroin in 40 micrograms ml-1(-1) mg ml-1 aqueous heroin hydrochloride solutions is 1.2%. The electrode exhibits good selectivity for heroin in the presence of a number of adulterants and basic organic compounds commonly present in illicit heroin powders. The method was applied to the direct potentiometric determination of heroin in illicit powders (10-36% heroin) and the results agreed fairly well with those obtained by gas - liquid chromatography.