Complexometric Analysis of Multicomponent Systems

Methods of complexometric analysis are reviewed with particular reference to their improved potential due to recent developments in theory and instrumentation. It is shown how accuracy has been improved and how reactions leading to the formation of compounds with rather low stability constants can be utilized successfully. For the analysis of multicomponent systems there are essentially two possibilities: (a) The components are completely separated and determined separately; (b) No separation is performed, and all determinations are made on the same sample solution. In the latter case the determinations may or may not demand appropriate masking procedures. When several components with very similar properties are present or when the various components require further investigation, complete separation may be necessary. But if only the composition of the sample interests the analyst, methods demanding no separation procedures are simpler and speedier. Therefore, in a symposium on Separation Methods' we should not completely forget one essential question: How can separations be avoided? Or, in the terms recently suggested by Dr Chalmers1 : How can literal' separations be replaced by figurative' separations? I think that every analyst is aware of the fact that the introduction of new complexing agents during the recent past has immensely enhanced the possibilities of analysing multicomponent systems—with or without prior separation. May I start with a discussion of analyses without any previous separation. The theoretical treatment of equilibria is the same for acids and for metal ions. The metal ions can be considered Lewis acids', or—if you prefer—— acids can be considered hydrogen complexes. In our system the species M1, M11 etc. may represent metal aquo ions or some other Brönsted acids, or some kind of Lewis acids. Generally speaking, a titrimetric determination of M1 in the presence of M11 is possible if the difference between the stability constants of the two complexes formed is sufficiently large and if the equivalence point can be detected with sufficient precision. If the difference is too small, M11 has to be masked by means of an appropriate masking agent. However, the masking 779