Application of poly (ethyleneimine) solution as a binding agent in DGT technique for measurement of heavy metals in water

A 0.050 mol L−1 solution of poly (ethyleneimine) (PEI), had been used as a novel binding agent of diffusive gradients in thin-films (DGT) technique (PEI-DGT) for measuring the concentrations of labile Cu2+, Cd2+ and Pb2+ in waters. The binding capacities of the PEI-DGT for Cu2+, Cd2+ and Pb2+ were 11.8, 10.2 and 10.6 μmol L−1, respectively. The performance of PEI-DGT was independence of pH in the range of 4–8 and ionic strength in the range from 1×10−4 to 0.1 mol L−1 (as NaNO3). PEI-DGT could measure 104.7±5.2% of the total concentration of Cd2+ (0.500 mg L−1), 95.2±4.3% of the total Cu2+ (0.500 mg L−1) and 99.2±3.4% of the total Pb2+ (0.500 mg L−1) in synthetic solution. Effects of the ligands on the measurement of labile metals were also investigated in synthetic solutions containing the various concentrations of EDTA and humic acid. In EDTA solution, the concentrations of labile metals measured by PEI-DGT showed good agreement with the theoretical concentrations of free metal ions. In humic acid solution, the concentrations of labile metals measured by PEI-DGT decreased with the increase of the concentrations of humic acid. Several DGT devices with various binding agents, including PEI, sodium polyacrylate and poly(4-styrenesulfonate) solution, were used for the measurement of labile fractions of Cu2+, Cd2+ and Pb2+ in the spiked waters and in mine wastewaters. The results showed that the concentrations of labile metal measured by DGT devices with different binding agents could be significantly different, indicating that the labile fractions of metals were dependent on the binding strength of the binding agents with metals. By choosing binding agents, the useful information on the speciation and bioavailability of the analytes can be provided.