Preparation of guanidinylated carboxymethyl chitosan and its application in the diffusive gradients in thin films (DGT) technique for measuring labile trace metals in water

Guanidinylated carboxymethyl chitosan (GCMCS) was prepared via the guanidinylation of carboxymethyl chitosan (CMCS). A device employing the diffusive gradients for thin films (DGT) technique was made using a GCMCS aqueous solution as the binding agent and a cellulose acetate dialysis membrane (CADM) as the diffusion phase to measure labile Cu2+, Pb2+ and Cd2+ in water. The percentage uptake (U%) values of labile Cu2+, Pb2+ and Cd2+ in a synthetic water sample were almost consistent with the theoretical values at 101.6 ± 2.8%, 104.6 ± 6.1% and 95.9 ± 4.4%, respectively. The optimum pH ranges for the measurement of labile Cu2+, Pb2+ and Cd2+ were 3.0–7.0, 3.0–7.0 and 4.0–8.0, respectively. The ionic strength mainly affected the diffusion of metal ions in the CADM. The diffusion rates decreased with increasing concentrations of NaNO3 solutions. The application of GCMCS-DGT in natural water and industrial wastewater showed that dissolved organic carbon (DOC) only affects metal species, and the accurate determination of labile Cu2+, Pb2+ and Cd2+ can be achieved when the diffusion coefficients of these metal ions in the diffusion phase have been determined. GCMCS is suitable for DGT application as a chelating agent for metal ions.