Photometric complex-formation titration of submicromole amounts of metal-II The presence of other metals.

End-point extrapolation with the aid of a tangent to the spectrophotometric titration curve has been discussed theoretically for the metal-indicator complex MI with a ligand L in the presence of two other metals (P(1) and P(2)). It was found that a titration end-point can only be determined when the reaction of P(1) and P(2) with L takes place only negligibly during the titration of M. Two cases of practical interest can be distinguished. The metals may react either before or after the titration has been completed. For both situations titration conditions have been derived. With these titration conditions suitable experimental conditions can directly be derived from diagrams which were introduced in a previous paper. The theory developed has been applied to mixtures of manganese and magnesium but is generally applicable.