A separation and preconcentration process for metal speciation using a liquid membrane: a case study for iron speciation in seawater

Abstract

An efficient assisted transport of Fe(III) ions using a bulk liquid membrane containing 2 hydroxybenzaldeyde benzoylhydrazone in toluene has been applied as a separation and preconcentration process for the analysis and speciation of dissolved iron traces in natural and sea waters. A study strategy based on a modified simplex design has been followed to optimise the transport of Fe(III) ions through the liquid membrane. Maximum carriermediated transport efficiencies were obtained at following conditions: pH 1.9 for feed aqueous solution; 0.014 mol L−1 of ligand in toluene as carrier and 2.9 mol L−1 HNO3 in the stripping solution. Under optimal conditions, the average recovery of Fe(III) ions was 102 ± 2% (n =7) for 6 h at 35 °C and the preconcentration factor of the method was 18.1. The influence of saline matrix was negligible and experiments at slightly high temperatures led to reduced preconcentration times. The accuracy of the method was verified by using the TMDA-62 certified reference water sample and successfully applied to the analysis of Fe(III) in river and seawater samples from Tangier (Morocco). Due to the proposed liquid membrane system allowed the selective separation and preconcentration of Fe(III) ions but not Fe(II) ions, a scheme for speciation analysis of dissolved iron was proposed. The distribution of total dissolved Fe, non-labile Fe, labile Fe(II) and labile Fe(III) fractions was performed in real seawater samples with successful results in good agreement with those obtained by adsorptive cathodic stripping voltammetry (average relative error of ± 3%).