Application of a lithium-ion selective metallacrown to extraction- spectrophotometric determination of lithium in saline water

Abstract

The solvent-extraction behavior of Li + and Na + with a Li + selective metallacrown, [(Ru(η 6 -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.