All-Solid-State Ion-Selective Electrodes Based on Graphite Paste for Determination of Calcium(II) and Nitrate

Robust and easy-to-handle ion-selective electrodes in all-solid-state configurations based on graphite paste have been developed for applications in environmental samples. The electrode consists of different functional layers (graphite paste, conducting polymer, ion-selective membrane). The ion-selective compounds have been incorporated in polyvinylchloride (PVC) membranes. Polypyrrole (PPy) acts as a solid contact and an intermediate layer between the ion-selective membrane and the graphite paste. As ion-complexing compounds tridodecylmethylammonium nitrate (TDMA-NO3) for nitrate, N,N,N’,N’-tetra[cyclohexyl]diglycolic acid diamide and N,N-dicyclohexyl-N‘,N‘-dioctadecyl-diglycolic diamide for calcium(II) determinations have been used. The electrodes have been tested in drinking and well water samples by direct potentiometric determination and by titrations. The results have been compared to ion chromatography as the reference method. Both ion selective electrodes exhibit linear response from 10-5 mol/L to 10-1 mol/L respectively. The detection limits for the target ions are below 10-6 mol/L based on the respective ion.