[Applicability Comparison and Application Study of Two Methods for Determination of the Copper Complexing Capacity of...

Complexing capacity (CC) is an important indicator affecting the environmental behavior of heavy metals in water, which can be determined by different methods based on different mechanisms. To validate and compare the applicability of different methods in CC determination, the complexing capacity of Cu²⁺ (CuCC) in solutions of ethylenediamine tetraacetic acid (EDTA) and acesulfame was determined by methods of dithizone extraction kinetics (DEK) and ion-selective electrodes (ISE), while EDTA and acesulfame were selected to represent strong and weak ligands in water, respectively. DEK method was found to be more suitable for determining the contribution of strong ligands to CuCC, while the results determined by ISE were related to both the strong and weak ligands in water. DEK and ISE methods were used to measure CuCC of several actual water samples, including samples from reservoir, discharge river, fishpond, and landfill leachates. CuCC in the water samples of the reservoir and discharge river measured by ISE were 86.9-227.0 μmol·L^-1, which were about one order of magnitude higher than those measured by DEK (9.9-14.6 μmol·L^-1). For the landfill leachates, CuCC measured by ISE were 6998.4-31005.8 μmol·L^-1, which were 2 orders of magnitude higher than those by DEK (89.6-109.1 μmol·L^-1). The increase of CuCC in the polluted water samples might be due to the weak ligands like pollutants. A positive correlation (R=0.975, P<0.01) was found between the CuCC related to the weak ligands (ΔCuCC) and the sum concentration of ammonia nitrogen and organic nitrogen in waters.