A chronoamperometric method to estimate changes in the membrane composition of ion-selective membranes

A new chronoamperometric method is used to estimate changes in the membrane composition of mobile-site, ionophore-based membranes. The characteristic features of the chronoamperometric curves (initial current, slope, break ti me) of valinomycin-based, potassium-selective membranes loaded with potassi um tetrakis(4-chlorophenyl)borate are correlated with the mobile-site and f ree ionophore concentration in the membrane. Limiting cases for strong and negligible ion pair formation are distinguished. Replicate measurements ind icate a relative standard deviation in the calculated values less than 10%. The practical applicability of the method was tested with membranes incorp orated into conventional ion-selective electrode bodies or cast onto microf abricated planar sensor structures.