Anion Interference in Response of Sodium Ion-selective Electrodes Based on a Bis(crown ether) Compound

Abstract

Anion interference in response of sodium ion-selective electrodes (Na-ISEs) based on a bis (crown ether) compound was studied by measurements of electromotive force(emf) of the Na-ISEs and ATR/FT-IR spectra of the membrane surface. Sodium ion-selective membranes consisted of bis[(12-crown-4)methyl] 2-methyl-2-dodecylmalonate [bis(12-crown-4)] as a ligand, plasticizer with a variety of dielectric constants and poly(vinyl chloride). It was found that higher dielectric constant- of the plasticizer led smaller Nernstian slope and narrower linear range for the Na-ISEs. Lipophilic anions such as SCN- affected the emf-response of Na-ISEs based on bis(12-crown-4). In order to eliminate the anion interference, it was effective to use a plasticizer with low dielectric constant and an additive like sodium tetraphenylborate or its derivatives, simultaneously. It seems that the optimum plasticizer and additive are dioctyl adipate (DOA) and sodium tetrakis[3, 5-bis(trifluoromethyl)phenyl]borate (NaTFPB), respectively. The optimum concentration of NaTFPB was 5-20 mol%for bis(12-crown-4) from the point of high electivity and exclusion of anion interference. The optimized Na-ISE was applied to the analysis of control serum and patient serum samples; good reproducibility and accuracy were obtained. We concluded that the Na-ISE optimized in this study would be highly useful in the field of clinical analysis.