NEW COCAINE-SELECTIVE MEMBRANE-ELECTRODE

The sensitivity and selectivity of a cocaine-selective membrane electr ode have been improved with the use of sodium tetrakis[3,5-bis(trifluo romethyl)phenyl]borate as an ion-exchanger and tetrakis(2-ethylhexyl) pyromellitate (TEHPY) as a solvent mediator. The use of TEHPY suppress ed the responses to lipophilic quatemary ammonium ions and strengthene d the response to cocaine. The electrode exhibited a near-Nernstian re sponse over a concentration range of 10(-2) to 10(-6) M cocaine with a slope of 56 mV per decade. The lower limit of detection was 4 X 10(-7 ) M cocaine. Interference by other drugs (morphine and codeine) and a stimulant (methamphetamine) was negligible. This electrode was applied for the determination of cocaine in a drug mixture containing cocaine and morphine, which is widely used to suppress acute pain in cancer p atients. The concentration of cocaine, different in each patient, was measured precisely with an average recovery of 99.9% and a mean relati ve standard deviation of 0.56%.