Pyrocatechol Violet as a Detection Reagent for Cations

Abstract

FOR the purposes of rapid identification of unknown substances on paper chromatograms, both general reagents reacting with a great number of substances irrespective of their nature, and selective reagents allowing a closer characterization of the particular substance play an important part. The most common detection reagents used in paper chromatography and electrophoresis of inorganic cations, which include hydrogen sulphide, 8-hydroxyquinoline and alizarin, react with a large number of cations. Other commonly used reagents belong to the group of selective agents which react only with a definite and rather small number of substances. Most of these reagents react with elements of various valencies and give no indication on the charge of the cation. In the search for a suitable reagent for the detection of thorium on paper electropherograms¹ use has been made of the detection with pyrocatechol violet, which has recently proved successful as an indicator for complexometric titrations since it forms coloured complexes with some cations, especially Bi^{3 +} and Th^{4 + 2}. Pyrocatechol violet is a catechol sulphophthalein with formula: