LOCAL ANESTHETIC-SENSITIVE ELECTRODES - PREPARATION OF COATED-WIRE ELECTRODES AND THEIR BASIC PROPERTIES IN-VITRO

Coated-wire electrodes with local anesthetic (LA) cation-selective mem branes were prepared, and their properties in vitro were investigated. Copper wires (0.8-mm diameter) were coated with gel membranes of 110 mg of poly(vinyl chloride), 5 mg of ion pairs of tetraphenylborate ani on with LA cation, 100 mg of dioctylphtalate, and 1.5 mL of tetrahydro furan. This was the composition determined to be most suitable. Their electromotive force relative to an Ag/AgCl electrode was measured in L A solutions. The lidocaine, dibucaine, and mepivacaine electrodes all showed good Nernstian response at 25-degrees-C in aqueous solutions in the concentration ranges of 1 X 10(-4) to 1 X 10(-2) mol/L, 4 x 10(-5 ) to 1 x 10(-2) mol/L, and 5 x 10(-5) to 1 X 10(-2) mol/L, respectivel y. The response time was within 10 s. The electrode potential decrease d as the pH in the solution increased, with a corresponding decrease o f the protonated form of LA. The hydrophobic nature of the LA was clos ely related to the electromotive force and to the selectivity of the e lectrode toward various LA cations. Dibucaine, the most hydrophobic, h ad the highest electrode potential. The more hydrophobic the LA of the electrode, the less it is interfered with by other LA molecules. The more hydrophobic the interferent cation, the more it acts on the elect rode potential. The electrode system could also measure LA in human pl asma at 37-degrees-C, although the responsiveness was depressed in the low concentration range owing to binding of LA to the serum protein. Its small size, convenience of handling, good response, and simplicity of measurement indicate the feasibility of the electrode system for i n vivo application.