A Method of Chemical Speciation of Metallic Elements Dissolved in Sea Water by Using XAD-2 Resin

Abstract

   A new method of determination of metal-organic complexes and compounds in sea water is developed using Amberlite XAD-2 resin. Neutral or basic metal-organic species are adsorbed on the resin at pH 8 and acidic ones are adsorbed at pH 3. Elution of each metal-organic compound is done by methyl alcohol and dilute NH₄OH. After decomposition of organic matters in the eluate, the determination of metallic elements is done by spectrophotometric, fluorometric or atomic absorption spectrophotometric methods. Although the ratio of organic species to the total varied from element to element, the reproducibility of the analytical result is excellent. The result of comparison with gel-exclusion method shows good agreement with that of the present method.
   The molecular size distribution of metal-organic species shows that the major fraction is involved in high polymer organic matters with molecular weight ranging from 1×10³ to 2×10⁴ daltons. The concentration of metal-organic species shows an intimate correlation with that of combined amino acids or proteins adsorbed on the resin, and composition of individual amino acids is specific for each molecular size group. Every result indicates the presence of stable metal-organic species in sea water and that the present method is one of the useful tools for chemical speciation of metallic elements dissolved in sea water.