Ionic strength effect on extraction of potassium complexed with crown ether 18-crown-6. Preliminary communication

As part of a broad study of the factors which affect extraction of salts of cations, complexed with an uncharged ligand, L, a critical study has been made of the extraction into dichloromethane of K+ complexed with 18-crown ether-6 in the form of picrate (LKPi). In using extraction analysis for the determination of very small concentrations of K+ in the presence of other salts activities of (K+)w and (Pi−)w in the aqueous phase must be written in the expression for Kext(LKPi). The salting out effect on P(L) = [L]0/[L]w can greatly affect the concentration of potassium ions left in the aqueous phase. Selectivity of K+/Na+ in extractions with 18-crown-6 has been determined.The extraction method is very suitable for the determination of traces of potassium in salts of sodium, magnesium, and calcium after calibration with, e.g., potassium chloride in potassium-free salts and also, after proper calibration, in routine analysis of liquids which contain little K+ and a large excess of Na+ (e.g. sea water, blood serum).