Primary-ion-conditioned polymeric membrane electrodes for sensitive detection of polyions

A novel operation mode for development of sensitive and renewable polymeric membrane polyion-sensitive electrodes has been explored in this paper. In contrast to the traditional polyion sensors which are conditioned with highly discriminated ions, the proposed polycation-sensitive membrane electrode with dinonylnaphthalene sulfonate as the ion-exchanger is conditioned with the primary ion (protamine), and activated with the discriminated ion (Na+) before measurement. Using this protocol, the membrane with protamine in the membrane bulk but with discriminated ions rich at the membrane outer surface can be prepared. The protamine inside the membrane efficiently suppresses the fluxes of protamine from the sample–membrane interface into the membrane bulk, thus decreasing the detection limit toward protamine by one order of magnitude. With the reproducible protamine fluxes obtained by the conditioning and activation steps, the protamine-sensitive electrode could be reused without significant signal deterioration. Titrimetric analysis of heparin with this novel technique has been demonstrated. The proposed polyion sensing platform offers much promise in the detection of polyions as well as in other polyion-involved bioanalyses.