Application of a Poly(4-styrenesulfonate) Liquid Binding Layer for Measurement of Cu2+ and Cd2+ with the Diffusive Gradients in Thin-Films Technique

A diffusive gradients in thin films (DGT) technique for measuring Cd and Cu is described using, for the first time, a liquid phase binding layer and a dialysis membrane diffusive layer. The binding phase was a 0.020 M solution of poly(4-styrenesulfonate) (PSS) polyelectrolyte using a specially designed DGT deployment device. The binding properties of Cd2+, Cu2+, and a range of alkali and alkaline earth metal ions to the PSS solution were characterized. The PSS behaved like a cation exchanger with preferential binding to Cd2+ (6.0 (mu)mol mL-1, log K = 9.0) and Cu2+ (2.5 (mu)mol mL-1, log K = 8.1) under competitive binding conditions. PSS had a substantial binding capacity at pH >3 and at competitive Na+ concentrations up to 1.0 M. The DGT devices were successfully validated for Cd2+ (accumulated mass vs time r2 = 0.969, recovery compared with predicted values = 98%) and Cu2+ (r2 = 0.980, recovery = 98%) in synthetic lake water (Windermere). Validation was also undertaken for Cu in a spiked local lake water (Parkwood Pond) (r2 = 0.981, recovery = 46%). The low recovery here was due to complexation of Cu by natural organic matter (14 mg C L-1). Field deployments of the DGT devices were successful at measuring Cu concentrations of 0.031-0.63 (mu)g L-1 in local fresh and salt waterways. These DGT-labile measurements were 0.05-39% of the 0.45-(mu)m-filtered Cu values.