Evaluation of potentiometric acid-base titrations by partial-least-squares calibration

Partial-least-squares calibration is used for the evaluation of acid-base titration curves. The method is advantageous because no physical model is assumed and only information from the titration curves is used. In the procedure, a model is developed from samples of known composition (calibration set) and is then used to predict unknowns (test set). The only assumption is that the two sets are similar. The method was evaluated first by titrating mixtures of two monoprotic acids with a small difference in pK_a values and then by titrating samples containing four or five diprotic acids. The results show that it is possible to determine monoprotic acids having a difference in pK_a of only 0.1, or up to five diprotic acids having pK_a values in the range 1.8–7.2, simultaneously.