Selective detection of bismuth(III) and iron(II) ions with certain new reagents

Isoperthiocyanic acid (3-amino-5-thione-1,2,4-dithiazole) (I), tetraethylthiuram monosulphide ("Tetmosol") (II), eosin (III), and mercurochrome (IV) are used as new qualitative reagents for bismuth, III and IV are also used for detection of iron(II). A conc. sulphuric acid solution of I, or an acctone solution of II, when treated with bismuth in presence of potassium iodide, gives a deep red or reddish-orange precipitate, characteristic of bismuth. Bismuth in presence of III or IV gives a heavy and characteristically bright deeppink precipitate on addition of ammonia. With I, 1 mug of bismuth may be detected with a dilution limit of 1:50,000. Sb(III) and As(III) do not interfere in any of these tests. Iodides interfere only when I and II are used as reagents. Pb, Cu(II). and Fe(III) interfere with III and IV. I and II are also proposed as reagents for iodide; nitrites would interfere. III and IV, with iron(II) on addition of ammonia, produce a precipitate with highly intense green fluorescence. No other common cation including Fe(III)] or anion interferes. The limit of detection is 3 mug ml .