I the ANALYST'S \ column * L.T.Hallett, Editor
X HE possible application of complexometiy to several areas where it is not now being used was included in a very interesting review entitled "Recent De velopments in Chelatometry." The au thor is Rudolf Pribil of the Czechoslovak Academy of Sciences, who gave the paper late last year before the Society for Analytical Chemistry in London. Use of the reagent E D T A (cthylenedinitrilo)tetraacetate, a.lso called Complexone. although less than a decade old, has become established as a new branch of volumetric analysis—complexometry. Practically the whole periodic system comes within the scope of this technique, except for the rare gases, a few elements of the first, fifth, and sixth groups, and beryllium, boron, and silicon. Its uni versality, however, hampers the applica tion m metal determinations in complex solutions. The principal objective of complexometry at present is to find ways and means of carrying out complexomctric titrations with the maximum selectivity. The major factors to be determined are those which affect, or prevent, complex forma tion by individual metals in solutions. The next important factors, Pribil says, are p H and the presence of strongly com plex-forming agents in the solution. If these were the only factors, com plexomctric problems might be solved by mathematical considerations. There are other complicating factors, however, in cluding ionic strength of the solution, effect of less polar solvents, and influence of competing equilibria involving the component ions of the complex. When a p H value has been determined which eliminates interferences by as many unwanted cations as possible, there arises the practical requirement of an in dicator which will give a good end point at this pH. In recent years more than 100 widely differing compounds have been proposed as metal indicators in various situations. The largest group are dyes forming solu ble complexes differing in color from the free dye. These are called met.allochromic indicators. A study of these compounds had led to conclusions as to the structural prereq uisites of metallochrome action, which in turn has made possible synthesis of several new and effective compounds. Metallochromic indicators generally
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VOL. 30, NO. 3, MARCH 1958
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