Intercomparison of DPASV and ISE for the measurement of Cu complexation characteristics of NOM in freshwater

Complexation by dissolved humic substances has an important influence on tr ace metal behavior in-natural systems. Unfortunately,few analytical techniq ues are available with adequate sensitivity and selectivity to measure free metal ions reliably at the low concentrations under which they occur in na tural waters. In the past, differential pulse anodic Stripping voltammetry with a thin mercury film rotating disk glassy carbon electrode (DPASV-TMF-R DGCE)has been used to measure complexation capacities and conditional, meta l-ligand binding constants in oceanic and estuarine waters. In contrast, fe w studies have been conducted to validate DPASV's use in freshwaters. The c urrent study compares DPASV and Cu ion-selective electrode (CulSE)methods f or measuring free copper, complexation capacities, and conditional binding constants on samples of synthetic and isolated natural organics. Titration data show that DPASV and CulSE are able to measure similar:amounts of labil e copper when the two methods' detection windows overlap. Furthermore, the greater sensitivity of DPASV allows it to measure free copper at lower conc entrations, which correlated well with CulSE data extrapolated into that sa me region. This strong correlation between these analytical methods provide s positive evidence for the use of DPASV (TMF-RDGCE) in measuring free Cu2, complexation capacities, and conditional binding constants in freshwaters .