Determination of total silver and silver species in coastal seawater by inductively-coupled plasma mass spectrometry after batch sorption experiments with Chelex-100 resin

Abstract

Sorption experiments in batch mode with Chelex-100 resin have been carried out for the determination of total Ag, labile and inert fractions in seawater from Ria de Vigo (NE Atlantic ocean) by inductively coupled plasma-mass spectrometry (ICP-MS). The method allows an accurate determination of the total Ag thus avoiding the effect of the saline matrix when direct determination by ICP-MS is performed. Similarly, the distribution patterns of Ag among species with different lability can be established in seawater as a function of pH. Species distribution and total Ag contents have been obtained in CRM CASS-4 (near shore seawater) and four coastal seawater samples. While the free silver ion concentration accounts for a significant fraction at low pH, the labile inorganic fraction is most important at natural pH (≈8) in non-polluted seawater. The inert and labile organic fractions were the most relevant in polluted coastal seawater. Complexation mechanisms of silver were also investigated from the sorption curves of silver on Chelex-100 according to the Gibbs-Donnan model. Two complexes were formed, AgL and AgL₂ with the following intrinsic complexation constants log β_(1np) = ?2.11 and ?10.02, respectively. The formation of the complex AgL predominates up to pH 4 but is negligible due to chloride ions effect, while the complex AgL₂ predominates from pH 4.