Ion sensing film optodes: disposable ion sensing probes for the determination of Na⁺, K⁺, Ca²⁺ and Cl^- concentrations in serum

Highly selective ion sensing film optodes for the determination of four kinds of ions (Na⁺, K⁺, Ca²⁺, Cl^-) were prepared with plasticized PVC membranes containing the respective ionophores and a newly prepared lipophilic anionic dye. The principle of the optical response of these sensing films is based on ion-pair extraction of the ion-ionophore complex and a deprotonated or protonated lipophilic anionic dye. These film optodes are for disposable use and can detect ions by simply immersing them into a glass vessel which is filled with the samples solution and determining the ion by measuring the absorbance change at the respective maximum absorption wavelength of the lipophilic anionic dyes in the visible region. The theoretical response of these films was also discussed based on the ion-extraction model. The ion selectivity of these films was sufficient for the determination of Na⁺, K⁺, Ca²⁺ and Cl^- in diluted serum samples, and satisfactory results were obtained in serum analysis.