Spectrophotometric determination of sodium by ion-pair extraction with crown ether complexes and monoanionic dyes

A highly selective photometric procedure for the determination of sodium in blood serum is proposed, based on the ion-pair extraction of a sodium—cryptand complex. A comparative study of cryptands with various cavity sizes, different pairing anions and extraction solvents is described. The use of cryptand 211, picrate and toluene, as ligand, pairing anion and extraction solvent, respectively, allows sodium to be determined at the μg ml^?1 level. A 350-fold amount of potassium (by weight) does not interfere, nor do other alkali metals. Possible interferences by multivalent cations are masked by EDTA.