Investigation of the metal species in seawater by sorption of the metal ion on complexing resins with different sorbing properties

The distribution of some metal ions in seawater samples among different spe cies was investigated by the resin titration (RT) procedure, based on the s eparation of the metal ion on resins with different sorbing properties. Two complexing resins were used for the titration of four metal ions (Cu(II), Cd(II), Ni(II) and Mn(II)): Amberlite CG 50 and Chelex 100. The first one i s a weak resin, able to sorb only the metal ion combined in weak complexes, or free, while Chelex 100 is a strongly sorbing resin, able to sorb also t he metal ion combined in strong complexes. The concentration of the total m etal ion completely sorbed and/or in equilibrium with the resin is obtained by RT. Also the reaction coefficient, i.e. the fraction of total to free m etal ion in the solution phase, in the presence of the resin, can be calcul ated. By comparing the titration with the two resins, three groups of speci es for each metal ion can be detected. For each of these, the reaction coef ficients are evaluated, or at least their limiting values. For example, the complexes detected with Chelex 100 in the seawater samples here examined h ad very high reaction coefficients: in the case of copper in one Ligurian S ea sample at pH = 7.1, log alpha ((M(I))) = 9.7 was found, for a complex co ncentration corresponding to 62% of the total metal ion. The rest of Cu(II) was linked to complexes with log alpha ((M(I))) near to 1, weak enough to be dissociated and sorbed on Amberlite CG 50. The proportion of the groups of complexes was different in the different samples examined, while the rea ction coefficients were similar. (C) 2001 Elsevier Science B.V. All rights reserved.