Synthesis and characterization of some chromogenic crown ethers as potential optical sensors for potassium ions

The complexing abilities of a series of chromogenic crown ethers for potassium and sodium ions have been investigated, by spectrophotometry for the reactions in solution, and by diffuse reflectance spectroscopy when the crown ethers were immobilized. The binding coefficients of the reagents increased with increasing negative charge in the cation-binding site and with increasing extent of chelation. Centimolar K(+) concentrations could be determined with the immobilized reagents, with a K(+)/Na(+) selectivity ratio of approximately 10.