Photometric complex-formation titrations of submicromole amounts of metals in the presence of an approximately equivalent amount of indicator.
The photometric titration of the metal indicator complex MI with a ligand L is discussed. A tangent procedure is adopted for the determination of the end-point. From this procedure, in combination with an assumed maximum titration error, titration conditions have been derived. A procedure is introduced which, in conjunction with the derived titration conditions, permits the selection of a suitable titration medium by means of a diagram in which log K, log alpha and log chi are plotted vs. pH. The procedure is applied to determination of lead and zinc in the presence of citric acid, the medium used for their paper-electrophoretic separation. The use of citric acid introduces some limitations; it is shown that the method developed is generally applicable.
Kragten
J
J
Natuurkundig Laboratorium, Universiteit van Amsterdam, The Netherlands.