Measurement Of Different Cu(â…¡) Species In Waters By Diffusive Gradients In Thin Films Technique

Diffusive gradients in thin films (DGT) technique is an in-situ passive method for the measurement of labile metals.The concentration measured of labile metals using the DGT devices with different binding phases is not the same, In this paper, the Cu(Ⅱ) species were measured by DGT devices with the 0.020M PSS and 0.003M PAAS solutions as the binding phases and cellulose dialysis membrane (CDM) as the diffusive phase.The conditional diffusion coefficients of Cu2+in the CDM with the PAAS and PSS as the binding phases were measured in the synthetic solution. The conditional stability constants of PAAS and PSS with Cu2+were also measured. The Cu(Ⅱ) species, including Cu(HCO3)2. Cu(NH3)4SO4 and CuCO3·Cu(OH)2 were accumulated and measured by CDM-PAAS-DGT and CDM-PSS-DGT at pH 5.5 and 7.5 in the synthetic solution. The effects of ligands (Gly, EDTA, and FA) on the measurement of DGT-labile Cu2+by two DGT devices at the different ratios of ligands to Cu2+were investigated. The conditional diffusion coefficients of Cu2+in the dialysis membrane were 3.389μcm2·s-1 for PAAS and 1 for PSS, The conditional stability constants(logK) of PAAS and PSS with Cu2+ were 7.025 and 5.214, respectively. At pH 7.5, the species of CuCO3·Cu(OH)2 and [Cu(NH3)4]2+could not be measured by two DGT devices, while the species of CuHCO3+and Cu(HCO3)2 could be messured. The concentrations of DGT-labile Cu(Ⅱ) of CDM-PAAS-DGT was more than that of CDM-PSS-DGT at pH 5.5 in Cu(HCO3)2, and CuCO3·Cu(OH)2 synthetic solution. This was because the speciation of CuCO3 Cu(OH)2 and [Cu(NH3)4]2+were changed at pH 5.5 and the binding strengths of PAAS and PSS for Cu(Ⅱ) were different. For the measurement of CuEDTA, the concentration measured of two DGT devices were in accordance with the theory value when the ratio of Cu2+to EDTA was 1:0.5, however, the concentrations of DGT-labile Cu(Ⅱ) could not be measured in CuEDTA synthetic solutions at the various ratios(1:1,1:2 and 1:5). These results showed that the complex of CuEDTA was DGT-inert and could not be accumulated and measured by CDM-PAAS-DGT and CDM-PSS-DGT. The concentrations of Gly and FA in synthetic solutions had a significant influence on the DGT-labile Cu(Ⅱ). The concentration of DGT-labile Cu(Ⅱ) of two DGT devices decreased with the increase of Gly and FA in synthetic solutions, while the concentrations of DGT-labile Cu(Ⅱ) of CDM-PAAS-DGT were more than that of CDM-PSS-DGT at the same deployment conditions. This was also because the binding strenghs of PAAS was stronger than that of PSS. The more logK of binding phase was, the higher DGT-labile concentration was.