Influence of nonionic surfactants on the optical response of cation selective membrane films

The effect of nonionic surfactants Triton X-100, and Brij 35 on the response performances of calcium, potassium and sodium optical sensors as well as chromophore only doped polymeric films was studied. Upon addition of surfactants, over five-fold enhancement of optical response was observed for potassium and barium ions at ionophore-free membranes. As to the two surfactants, the response enhancement is Triton X-100 30-50% greater than Brij 35. For calcium ionophore ETH 129 or ETH 1001 doped membranes using anionic fluorescein dye as chromophore, no significant effect of the surfactants on the calcium response and selectivity were observed. For the calcium membranes based on ETH 1001 and chromophore ETH 5350, the selectivity for calcium over potassium decreased more than two orders of magnitude by these nonionic surfactants. The effect of the surfactants on potassium ion sensors based on valinomycin is relatively small. For sensors using sodium ionophore-VI, the response enhancement by Brij 35 and X-100 at 5 x 10(-5) M was 12 and 20%, respectively, but the selectivity for sodium over potassium and barium ions decreased dramatically. The polymeric films doped only with chromophores such as DCFOE or ETH 5350 were found to be selective and useful for the determination of nonionic surfactants, Triton X-100 and Brij 35, in the range of 5 x 10(-6) M to 3 x 10(-4) M using 0.1-0.01M potassium or barium ions as background. (C) 1999 Elsevier Science B.V. All rights reserved.