Evaluation of Cu-ethylenediamine metal ion buffers as calibrants for ion-selective electrode measurement of copper in fresh water systems

An investigation was made into the accuracy of cupric ion selective electrode (ISE) measurement of Cu in solutions approximating acidic freshwaters with Cu-ethylenediamine buffers used as the calibrants. This method overestimates the free Cu compared with calibration using Cu(NO ) standards, the standard addition method, and speciation modelling calculations. Statistical tests showed a small, but significant, difference between the intercepts of the linear Nernstian regressions of the calibration plots of Cu-en buffer standardisation and direct calibration with Cu(NO ) standards in matrix that matches the samples. The difference in the intercepts, which corresponds with E values of the electrode, is not well understood, but is possibly caused by potentially interfering cations such as Fe2+. The results of this study showed that down to 10 M Cu , where a linear Nernstian response is possible, the Cu ISE is probably better calibrated using Cu standards prepared in the same matrix as the sample solutions to avoid potential matrix effects