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

A study was conducted to optimize a flow injection, solvent extraction, spectrophotometric procedure for the determination of potassium in freshwaters. Three analogues of 18-crown-6 were examined as the crown ether, 4 analogues of the anionic azo dye, 4-(4-dialkylaminophenyl)azo-2,5-dichlorobenzene sulphonate, and picrate were examined as counter anions, and approximately 10 different solvent systems were investigated. Optimal conditions involved the use of 4-(4-diethylaminophenyl)azo-2,5-dichlorobenzene sulphonate and benzo-18-crown-6 reagents with benzene-chlorobenzene (1:1 by volume) as the preferred solvent for extraction. The carrier stream was distilled water and the reagent stream contained the dye anion, crown ether, EDTA dilithium salt and lithium hydroxide. A PTFE porous membrane was used for separating the organic phase. The reagents used had the advantage of being readily soluble in water, of minimizing interferences from other ions (magnesium, sodium, calcium, ferric, ammonium) and of achieving good reproducibility and sensitivity. Sampling rates of 20 per h were achieved with a detection limit of 1 uM and a relative standard deviation of 0.4 per cent.