A Solid-Contact Ion-Transfer Stripping Voltammetric Sensor for Reagent-Free Orthophosphate Determination in Tap Water

Excess phosphorus loading is a major contributor to eutrophication and harmful algal blooms, creating a need for rapid, reliable, and field-deployable phosphate monitoring technologies. In this study, a novel reagent-free electrochemical sensor for orthophosphate determination was developed based on ion-transfer stripping voltammetry (ITSV) at a phosphate-selective membrane interface. The sensor consisted of a poly(vinyl chloride) (PVC)/o-nitrophenyl octyl ether (o-NPOE) membrane containing tributyltin chloride (TBTC) as a phosphate-selective ionophore integrated with a PEDOT:PSS solid-contact transducer for efficient ion-to-electron signal conversion. Orthophosphate was quantified through the controlled transfer of H2PO4− ions across the membrane without the use of chemical reagents, enzymes, or redox mediators. Under optimized conditions, the sensor exhibited a linear response over the concentration range of 10–850 μM with high linearity (R2 = 0.9955) and a limit of detection of 2.8 μM. The corresponding limit of quantification (LOQ) was 9.4 μM. Chronoamperometric measurements provided rapid concentration-dependent responses over a broader range of 5–1000 μM, demonstrating the potential applicability of the platform for future real-time monitoring applications. The sensor also maintained strong analytical performance in tap water samples and in the presence of chloride, sulfate, and nitrate ions, with detection limits ranging from 3.8 to 4.7 μM. To the best of our knowledge, this work represents the first demonstration of a solid-contact ITSV sensor for direct orthophosphate determination and offers a simple, low-cost, and reagent-free approach for phosphate monitoring in aqueous systems.