title: Ion-pair extraction and fluorimetric determination of potassium with 18-crown-6 and eosin.
abstract: A highly sensitive and selective fluorimetric determination of potassium is proposed, based on solvent extraction of the ion-pair formed between a large anion and the cationic complex of K(+) with a crown ether. Sensitivity is achieved by selection of a highly fluorescent counter-ion of the fluorescein group (eosin). A linear working range from 0.01 to 1 ppm of potassium is obtained, which gives a higher sensitivity than any similar method for potassium determination. The relative standard deviation is 4-5%. Selectivity is achieved by matching the radius of the cavity of the 18-crown-6 to the ionic radius of potassium. The system used is exceptionally selective for extraction of potassium in the presence of alkali or alkaline-earth metal cations. The proposed method has been successfully applied to the determination of potassium in blood serum.
authors.affiliation: Departamento de Química Analítica, Facultad de Ciencias, Universidad de Oviedo, Oviedo, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Sanz-Medel
authors.forename: D B
authors.initials: DB
authors.lastname: Gomis
authors.forename: J R
authors.initials: JR
authors.lastname: Alvarez