All-solid-state chloride sensors based on electronically conducting, semiconducting and insulating polymer membranes

All-solid-state chloride sensors based on different types of polymeric membranes on a glassy carbon (GC) substrate were studied. Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with chloride was electrodeposited on the GC substrate, resulting in a GC/PEDOT sensor where PEDOT worked both as ion-to-electron transducer and sensing membrane. A classical solid-contact electrode was prepared by coating PEDOT with a layer of plasticized poly(vinyl chloride) (PVC) containing tridodecylmethylammonium chloride (TDMACl) as ion-exchanger. A non-classical solid-contact electrode was prepared by coating PEDOT with a layer of electronically semiconducting poly(3-octylthiophene) (POT) containing TDMACl as ion-exchanger as well. These GC/PEDOT, GC/PEDOT/PVC-TDMACl and GC/PEDOT/POT-TDMACl electrodes were compared with a GC/POT-TDMACl electrode. These combinations of polymeric membrane materials with different electronic and ionic conductivities were studied by electrochemical impedance spectroscopy (EIS) and potentiometric measurements. The results show that PEDOT offers highly reversible ion-to-electron transduction and the GC/PEDOT/PVC-TDMACl electrode gives the lowest hysteresis in the calibration plot among the electrodes studied. Interestingly, GC/POT-TDMACl gives a significantly lower detection limit than the other electrodes studied in this work. Furthermore, GC/POT-TDMACl shows a diffusion-controlled ion-to-electron transduction mechanism, which is clearly different from that of GC/PEDOT-based electrodes.