Development a flow rinsing system for improving the detection limit of solvent polymeric membrane ion-selective electrodes

In order to improve the lower detection limit of solvent polymeric membrane ion-selective electrodes (ISEs), a flow-through system with an ISE based on a highly selective and lipophilic Pb²⁺ ionophore, ETH5435, was constructed. This flow-through system has a function to remove most Pb²⁺ remaining at the phase boundary of the ISE membrane with feeding EDTA chelating solutions just before sample feeding. By feeding a trace level of Pb²⁺ solutions into the flow-through system, transient potentiometeric responses for Pb²⁺ were observed in the concentration range of 1×10^–9 mol L^–1 to 1×10^–6 mol L^–1 which was lower than the detection limit of conventional Pb²⁺-ISEs. The observed transient potential responses were analyzed based on an ion-flux model across the membrane/sample solution interface. As a result, it was found that plotting the gradient of the transient potential response immediately after sample feeding provides a calibration curve with good linearity from a sub-ppb to ppb Pb²⁺ concentration range.