THE APPLICATION OF VARIOUS IMMOBILIZED CROWN-ETHER PLATINUM-MODIFIED ELECTRODES AS POTENTIOMETRIC AND AMPEROMETRIC DETECTORS FOR FLOW-INJECTION ANALYSES OF CATECHOL AND CATECHOLAMINES

Different crown ethers were electrochemically polymerized or adsorbed onto a platinum electrode for the analysis of catechols by either stat ic potentiometric, potentiometric FIA or amperometric FIA. The static potentiometric responses of all the crown ether modified electrodes we re linear over about three decades of catechol concentration (10(-5)-1 0(-8) M). The potentiometric FIA response of all the crown ether modif ied electrodes exhibited linear responses over four decades of catecho l concentration (10(-2)-10(-6) M). The amperometric FIA responses were linear over a 10(-2)-10(-5) M range. Comparing the different techniqu es; static potentiometric, potentiometric FIA, and amperometric FIA, a ll had markedly different response slopes for the different crown ethe rs. Overall, the crown ether modified electrodes, except for an open-c rown ether, displayed excellent response stability for successive inje ctions in both FIA modes. The lowest detection limits were about 0.5 x 10(-6) M for the potentiometric FIA with minimal interference from as corbic acid, uric acid and acetaminophen. For amperometric FIA the det ection limits were about 0.5 x 10(-5) M, but for ascorbic acid, uric a cid, and acetaminophen the interference was significant. Experimental parameters which influence the mechanism of the potentiometric respons e are discussed.