New applications of certain common organic dyes (acriflavine, eosin, and mercurochrome) in inorganic qualitative analysis. Detection of bromide, bromate, thallium(I), lead(II), cadmium(II), copper(II), and iron(III).

Abstract

The common antiseptic dye acriflavine (I) is used as a reagent for the detection of bromate. Similarly, the dyes eosin (C. I. Acid Red 87) (II) and mercurochrome (merbromin) (III) are used in various ways for the detection of Br−, Tl(I), Pb(II), Cd(II), Cu(II), and Fe(III) ions. A solution of bromate mixed with I gives an orange precipitate on acidification; Br− does not interfere. Pb(II) gives a characteristic deep bright red colour or precipitate with II or III at pH 5–7. At lower pH, Pb(II) is detected by adding II or III followed by ammonia or a liquid aliphatic primary amine (ethylamine, n-butylamine, or allylamine), a bright deep red precipitate being formed. Cd(II) is detected by adding II or III, and then pyridine, when a deep bright pink precipitate results. If pyridine is replaced by sodium diethyldithiocarbamate solution, Tl(I) also gives a similar precipitate. A solution of Tl(I) mixed with II or III gives a very bright pink or reddish-pink precipitate with bromide. This test is also useful for the identification of Tl(I). Cu(II) gives a purple-violet solution with intense green fluorescence with II or III when the solution is made alkaline with ammonia. A similar colour and fluorescence are obtained with Fe(III) treated with II or III followed by potassium ferrocyanide. Fe(II) does not give this test. The nature of the products formed in the various tests is discussed.