Rotating Ion‐Selective Membrane Electrodes for Trace‐Level Measurements

Abstract

AbstractIon‐selective solvent polymeric membrane electrodes (ISEs) are shown to exhibit improved response characteristics in a rotating electrode configuration. With a rather concentrated internal electrolyte solution of primary (analyte) ions, which induces their leaching from the membrane into the sample, the detection limit of the ISEs rotating at 3000 rpm is found to be better by about one order of magnitude than that of the analogous conventional ones in a stirred solution. On the other hand, with an internal solution inducing a strong inward flux of primary ions (i.e., from the sample to the ISE membrane), the apparent super‐Nernstian response due to depletion of primary ions from the analyte solution near the membrane surface is shifted by about one order of magnitude to lower concentrations. Membranes of about 0.8 mm diameter positioned eccentrically with respect to the rotation axis give a further shift of the apparent super‐Nernstian response step by about 0.3 logarithmic units. Simultaneously, the use of rotating electrodes substantially lowers the response time at submicromolar activities. An eccentrically placed Pb2+‐selective membrane on a rotating disk electrode with optimized internal solution shows a lower detection limit of aPb=6.3×10−11 M.