OPTICAL SENSOR FOR CALCIUM - PERFORMANCE, STRUCTURE, AND REACTIVITY OF CALCICHROME IMMOBILIZED AT AN ANIONIC POLYMER FILM

A calcium-selective optical sensor has been fabricated by the electrostatic immobilization of calcichrome at a porous anion-exchange polymer film. The change In the optical properties of the bound indicator as a function of Ca(II) concentration was monitored in a single-beam diffuse reflection mode at a pH of 12.1. Advantageous features of this design include a short response time (<15 s), high selectivity, facile construction, and compatibility with commercially available instrumentation. The rapid response results from the porous microstructure of the anion exchange polymer, which facilitates the mass transport of analyte and counterions between solution and polymer film. The optical response Is linear for a Ca(II) concentration between 3 and 30 mM with a detection limit of 3 mM. Immobilization alters both the acid and chelation strength of the Indicator. Possible causes of these reactivity differences are discussed, based on insights provided by Infrared internal reflection and photoacoustic spectroscopies. Equations to determine the metal complex formation constant and acid dissociation constants of the immobilized agent from diffuse reflectance spectra are developed. © 1990, American Chemical Society. All rights reserved.