Solid-phase colorimetric determination of potassium.

A nonpolar organic film (plasticized polyvinyl chloride) containing the ionophore valinomycin was incubated with an aqueous solution containing potassium ion and a detectable anion (erythrosin B). The amount of erythrosin B retained by the film after washing could be measured by absorbance or reflectance, and was directly related to the potassium concentration. This dye-binding method is quantitative for potassium and is suitable for both aqueous and serum-based solutions. There was no interference by sodium in the range found in serum. Several polyvinyl chloride plasticizers and anionic dyes and some other ionophores were found to be useful. The anion binding is thought to be restricted to the surface.