Preparation of ion-selective membrane and electrode using cobalt porphyrin as ionophore for anion detection

Abstract

In this study, the synthesis of the 5,10,15,20-tetrakis(4-dodecyloxyphenyl)porphyrin cobalt(II) complex (CoL) was carried out through a condensation reaction of 4-n-dodecyloxybenzaldehyde and pyrrole, followed by the metalation reaction of cobalt(II) acetate with meso-tetra(4-alkyloxyphenyl) porphyrin (L2) to obtain CoL. Characterization of CoL was conducted using physical methods such as 1H-NMR, 13C-NMR, and MALDI-TOF to confirm CoL structure and purity. CoL was utilized as an ionophore to fabricate the ion selective membrane (ISM) and ion selective electrode (ISE) for the detection of ClO4-. The composition of the ISM, including polymer (PVC), plasticizer (NPOE), cationic additive (TDMACl), and ionophore (CoL), was optimized for ISE fabrication. Various amounts of CoL and TDMACl were examined to determine the optimal conditions of the ISE. The optimized membrane components consisted of 33 wt% PVC, 66 wt% NPOE, 0.30 µmol CoL, and 60 mol% TDMACl compared to CoL. The fabricated ISEs exhibited a potentiometric response of -57.60 mV/decade (R2 = 0.99) within a concentration range of 1x10-6 to 1x10-2 M for ClO4- detection. The detection limit was determined to be 2.13 × 10-6 M. Selectivity coefficient analysis using the separate solution method (SSM) demonstrated that ClO4- displayed the highest selectivity coefficient among other ions, with a detection limit of 2.13x10-6 M. The fabricated ISE demonstrated good reversibility and stability when measuring solutions within the pH range of 3 to 12. Furthermore, the fabricated ISEs were successfully applied to water samples, including different brands of drinking water, and exhibited satisfactory performance. Additionally, the fabricated ISEs showed promising characteristics for continuous monitoring and analysis of ClO4- in water samples.