Spectrophotometric determination of potassium in river water based on solvent extraction of the complex formed with a crown ether and an anionic azo dye using flow injection

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Abstract
Potassium in water was determined by a spectrophotometric method involving flow injection coupled with solvent extraction. An ion association complex formed between the potassium-crown ether complex ion and an azo dye anion was extracted into an organic solvent and the absorbance of the separated organic phase was measured. Picrate and four analogues of 4-(4-dialkylaminophenyl)azo-2,5-dichlorobenzenesulphonate were examined as counter anions and three analogues of 18-crown-6 were examined as the crown ether. The use of several solvents was investigated. The results showed that 4-(4-diethylaminophenyl)azo-2,5-dichlorobenzenesulphonate and benzo-18-crown-6 were the most suitable reagents, benzene-chlorobenzene (1 + 1 V/V) being used for solvent extraction. The carrier stream was distilled water and the reagent stream contained the dye anion, crown ether, EDTA (dilithium salt) and lithium hydroxide. The organic phase was separated with a PTFE porous membrane. The sampling rate was 20 per hour. The calibration graph was linear at concentrations below 1 × 10–4 M using samples of 20 µl. The detection limit corresponding to a signal to noise ratio of 3 was 1 × 10–6 M and the relative standard deviation was 0.4%. Potassium in river water was determined satisfactorily by the proposed method.

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