Determination of metal ions concentration and speciation in seawater by titration with an iminodiacetic resin

A chelating resin containing iminodiacetic groups, Chelex 100 which is ofte n employed for sorbing metal ions from complex matrices, was used for separ ating and preconcentrating heavy metal. ions from seawater samples. The res in titration method was applied for determining the total concentration. Th e experimental procedure consists of measuring the concentration of the met al sorbed on Chelex 100 from solutions with different ratios volume of aque ous phase/amount of resin. The total metal ion concentration is obtained fr om the experimental data by a model for the sorption on the resin, the para meters of which are obtained by a non-linear regression procedure. In this way not only the total metal ion concentration can be determined, but also the side reaction coefficient alpha(M(1)), if the sorption equilibria of th e considered metal ion on the resin are exactly known, as is the case of Ch elex 100 considered here, The resin titration with Chelex 100 was utilized for determining the total metal ion concentration in certified seawater sam ples and real samples from the Ligurian Sea. It allowed the simultaneous de termination of the total concentration of manganese(II), cadmium(II), nicke l(II) and copper(II), in acceptable agreement with the certified values, Mo reover, the side reaction coefficients of some complex species could be eva luated. They were very high, and strongly dependent on the acidity of the s ample solution. For instance, values varying from 10(9) to 10(11) were obta ined for copper (II) in the different samples considered, at pH around 7, C helex 100 is such a strong sorbing substance that it is able to compete wit h the stable complexes for the combination with the heavy metal ions consid ered here. (C) 1999 Elsevier Science B.V. All rights reserved.