The solvent-extraction behavior of Li+ and Na+ with a Li+ selective metallacrown, [{Ru(η6-3,5-dimethylanisole)(2,3-pyridinediolate)}3], was investigated in the presence of organic dye anions, 3',3″,5',5″-tetrabromophenolphthalein ethyl ester ([TBPE]-), 2,6-dichloroindophenolate, and picrate ([pic]-). Each alkali metal ion was extracted as a 1:1:1 ternary complex of the metal ion, metallacrown, and anion. The Li+/Na+ extraction selectivity is anion dependent and highest with [pic]-. Therefore, we devised an extraction-spectrophotometric determination method for Li+ in saline water based on the extraction of Li+ using the metallacrown and [pic]- for high selectivity and subsequent replacement of [pic]- in the extracted species with [TBPE]- for high sensitivity. When applying this to artificial seawater samples containing known concentrations of Li+, a linear relationship was observed between the absorbance at 571 nm of the organic phase and the Li+ concentration in the samples. By this method, the determination of Li+ at the sub-ppm level in natural seawater is possible.
Keywords: Lithium; extraction–spectrophotometric determination; metallacrown; seawater.