Determination of Water Uptake of Polymeric Ion-Selective Membranes with the Coulometric Karl Fischer and FT-IR-Attenuated Total Reflection Techniques

Abstract

The water uptake of plasticized poly(vinyl chloride) (PVC) and silicone rubber (SR) based calcium-selective membranes which are commonly used in solid-contact and coated-wire ion-selective electrodes (SC-ISEs and CWEs) was quantified with the oven based coulometric Karl Fischer (KF) technique. Two different membrane types were studied: (1) the plasticized PVC or SR (RTV 3140) membrane matrix without other added membrane components and (2) the full Ca(2+)-selective membrane formulation consisting of the membrane matrixes, potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate and calcium ionophore IV (ETH 5234) or calcium ionophore I (ETH 1001). The membranes were contacted for 24 h either asymmetrically from one side or symmetrically from both sides with deionized water (DIW) or 0.1 M solutions of CaCl(2), KCl, or NaCl. It was found that the water uptake was higher for symmetrically contacted membranes. The highest water uptake (0.15-0.17 wt %) was obtained for the plasticized PVC based Ca(2+)-selective membranes in DIW, whereas the water uptake was lower in 0.1 M electrolyte solutions. Symmetrically contacted Ca(2+)-selective SR membranes had much lower water uptake in 0.1 M CaCl(2) (0.03 wt %) than their plasticized PVC counterparts (0.1 wt %). However, the (noncontacted) SR membranes contained initially much more water (0.09-0.15 wt %) than the PVC membranes (0.04-0.07 wt %). Furthermore, in good accordance with the KF measurements, it was verified with FT-IR-attenuated total reflection (ATR) spectroscopy that the water content at the substrate/membrane interface and consequently in the whole membrane was influenced by the electrolyte solution.

Electrocontrolled Swelling and Water Uptake of a Three‐Dimensional Conducting Polypyrrole Hydrogel

“…The results confirm that the swelling measurement of the hydrogel cannot be directly associated with water uptake. The obtained results are in accordance with other studies reporting that the water uptake of plasticized poly(vinyl chloride) membranes is higher in deionized water than in 0.1 m aqueous solutions of CaCl 2 , KCl, and NaCl …”

Pre-Polarized Hydrophobic Conducting Polymer Solid-Contact Ion-Selective Electrodes with Improved Potential Reproducibility

“…We found that it is better to make the potential adjustment of the SCs before 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 Water uptake of the PPy-PFOS solid contact. The water uptake of plasticized PVC-ISMs has been recently characterized by the FTIR-ATR spectroscopy 29,30,68 and the oven based coulometric Karl Fischer titration technique. 68 It was shown that water diffuses readily through the PVC-ISMs and that the water content of the membrane is influenced by the chemical composition of the electrolyte solution contacting the ISM.…”

“…The water uptake of plasticized PVC-ISMs has been recently characterized by the FTIR-ATR spectroscopy 29,30,68 and the oven based coulometric Karl Fischer titration technique. 68 It was shown that water diffuses readily through the PVC-ISMs and that the water content of the membrane is influenced by the chemical composition of the electrolyte solution contacting the ISM. It was found that the water content was highest when the ISM was in contact with deionized water while the water content of the ISM decreased in 0.1 M CaCl 2 solution.…”

Application of Photocured Polymer Ion Selective Membranes for Solid-State Chemical Sensors

“…One of the primary causes of failure in these sensors is penetration of water through the membrane. Due to the water uptake, thin aqueous layers or pools of water can be formed at the membrane/electrode interface in potentiometric solid-contact ion sensors resulting in potential instability and poor membrane adhesion to the solid contact [3].…”