Determination of mixed metal ions by complexometric titration and nonlinear partial least squares calibration

Many metal ions react with aminopolycarboxylic acids, such as ethylenediaminetetraacetic acid (EDTA) and ethylene glycol-bis(2-aminoethyl ether)-N,N,Nʹ,Nʹ-tetraacetic acid (EGTA), to form sufficiently stable chelates. In these reactions, hydrogen ions are released and the pH of the solution will decrease as those complexing agents are added into the vessel if the solution is not buffered to a constant and predetermined pH. In this situation, the complexometric titration procedure can be assumed as a acid-base titration. In this paper, a nonlinear model between the composition of the mixed metal ions and the measured pH responses in titration procedures was established, and was then used to predict unknown mixed metals. The developed method was evaluated by titration of mixtures containing two or three metal components with concentration levels from 8 × 10−4 mol l−1 to 4.2 × 10−3 mol l−1 and acceptable results were obtained.