INFLUENCE OF NONIONIC SURFACTANTS ON THE POTENTIOMETRIC RESPONSE OF ION-SELECTIVE POLYMERIC MEMBRANE ELECTRODES DESIGNED FOR BLOOD ELECTROLYTE MEASUREMENTS

The effect of the nonionic surfactants Brij 35 and Triton X-100 on the selectivity of neutral carrier-based ion-selective electrodes (ISEs) commonly used for measurements of electrolytes in whole blood is inves tigated. Studies are conducted with plasticized PVC membranes doped wi th several neutral ionophores commonly employed to prepare clinically useful potassium, calcium, and sodium ISEs. An observed increase in th e electrodes' EMF values upon the addition of surfactant to the test s olution suggests a change in the ion selectivity of the polymeric memb ranes in the presence of Brij 35 or Triton X-100. For membranes doped with K+-selective valinomycin, the effect of nonionic surfactants is r elatively small. However, in the case of calcium-selective membranes p repared with ETH 1001 and ETH 129, nonionic surfactants, especially Tr iton X-100, decrease the selectivity for calcium over potassium cation s by nearly 1 order of magnitude. Such behavior is even more dramatic for sodium-selective membranes, with the degree of surfactant-induced loss of ion selectivity dependent on the specific sodium ionophore emp loyed, the lipophilic tetraphenylborate derivative content of the memb rane, and the surfactant type. A detailed theoretical model is present ed to explain the effect of nonionic surfactants on the EMF response f unction of cation-selective polymeric membrane electrodes. Experimenta l results are in good agreement with theoretical predictions based on known binding constants for ionophores and surfactants with given cati ons.