The fraction of NiEDTA is between 3 and 25% of total EDTA,
being usually below 10%. Calculations based on known stability
constants and measured concentrations of metals, EDTA, and
some natural ligands for Cu and Zn show that NiEDTA should
be the most important species (up to 100% of EDTA should be
present as NiEDTA). The determination of NiEDTA, however,
gave much lower concentrations. This may be due either to slow
coordination kinetics of the exchange of dissolved nickel to the