Experiment 7: Results
Calibration and Cu-Titration of a Santa Ana River water sample

The titration data, resulting from the titration of the background buffered electrolyte, is plotted below.

These variations can be linearized, using the Nernst function, by determining the concentration of Cu²⁺ in the solution as a result of the addition of the Cu-titrant. Lets plot the change in potential as a function of the logarithm of the Cu²⁺ concentration. One obtains a linear relationship from which one can determine, by standard statistical methods the slope (kT/n) and the intercept (E_Cu-ISE):

In a second step, one replaces the background electyrolyte solution by a filtered water sample, buffered by the stock background electrolyte prepared previously. The graph of the titration data becomes:

Using calibration values, one can determine the free Cu²⁺ concentraton in the sample from which we can determine the extent of the complexation of Cu in the solution. To obtain the organic Cu complexation information, one needs to deduct the contribution of the inorganic species to the complexation of Cu. This is achieved by using a chemical speciation model that determine the different fractions of Cu-inorganic during the titration

The extent of total Cu complexation in the Santa Ana River water sample.