Separation and transport of lithium of 10 -5 M in the presence of sodium chloride higher than 0.1 M by 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin

Abstract

A water-soluble porphyrin (2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H 2(obtpps) 4−, H 2P 4−) synthesized in our laboratory was applied to a solvent extraction method and a liquid membrane transport of lithium as low as 10 −5 M (M=mol dm −3) in the presence of sodium chloride higher than 0.1 M. The lithium porphyrin with five negative charges was extracted successfully into chloroform with tetrabutylammonium ion (But 4N +) at pH 12.7. The extraction constant for the reaction of [LiP 5−] a+5[But 4N] + a⇌[(But 4N) 5LiP] o was found to be (1.9±0.3)×10 18 M −5, where the subscripts a and o denote chemical species in aqueous and organic phases, respectively. Lithium was transported to an aqueous phase at pH 7 through a chloroform liquid membrane containing [(But 4N) 5HP]. The extraction and transport mechanism was discussed on the basis of extraction constants, chemical species and transportation rate. Lithium in sea water or serum sample was separated and its concentration was determined spectrophotometrically by the present method without any interference from sodium chloride. The interference from transition and heavy metal ions was masked by Mg-EDTA. A calibration curve was linear over a range of 2×10 −6 to 2×10 −5 M at a precision of 1.51% (RSD).