Catechol violet indicator

Dilute a suitable aliquot of a solution in nitric acid, containing about 120 mg of bismuth, to 50 ml with water ensuring that only sufficient acid is present to prevent precipitation of the metal. Add 0 1 g of sulphamic acid and allow to stand for two minutes. Add 2 drops of catechol violet indicator and, if the solution is violet in colour, add dilute ammonia... 

To 100 ml of a neutral solution containing about 20 mg of manganese add a small amount of hydroxylamine hydrochloride to prevent oxidation of the manganese. Then add 10 ml of ammonia buffer solution followed by 3 to 5 drops of catechol violet indicator and titrate immediately with 0 01 M EDTA until the colour changes from greenish-blue to reddish-purple. 1 ml O OIM EDTA = 0 0005493 g manganese. 

Procedure. To one drop of the test solution is added one drop of cone, hydrochloric acid, one drop of a saturated solution of EDTA (free acid) and one drop of a 0.1 % aqueous solution of catechol violet. A blue-violet color indicates the presence of tantalum. 

Procedure. The paper chromatogram or filter paper on which the test solution has been spotted is sprayed with a solution of catechol violet. Mono- or dialkyl or aryl tin compounds are indicated by blue stains. 

Procedure. To one drop of the sample on a spotting plate is added one drop of ammonium acetate bujffer (pH 8.7), one drop of 0.1% catechol violet solution, 1 drop of 3% boric acid solution, and 1 drop of 3% hydrogen peroxide to mask cerium. A blue color indicates the presence of yttrium. 

By using ion exchange resins, 0.01 y Zr can be detected. A few granules of Amberlite IRA-411 (sulfate form) are mixed on a porcelain tile with 1 drop of 1 iV sulfuric acid-1 M K2SO4 (3 1), 1 drop of 0.5 % aqueous catechol violet solution and 1 drop of an acid (0.1 N) solution of the sample. A deepening of the orange-yellow color of the resin or the appearance of a blue color indicates the presence of Zr. Interference is caused by Bi, Hg, Al, Cu and Fe. ... 

There are now many metallochromic indicators which may be used in complexometric titrations. For successful end-point indication the pK value of the metal-dye complex should be at least 4 units less than that of the metal-EDTA complex which is formed during the titration if the difference is less than 4 units the titrant is unable to compete satisfactorily with the indicator dye and a sluggish end-point results. The indicators which are most widely used in the methods described in this book are solochrome black (for titrations carried out in ammoniacal solution), xylenol orange (for titrations carried out between pH 4 and 7) and catechol violet (for titration in mineral acid solution at pH 1 to 2). Table 63 lists the various indicators called for in methods in the monographs. Discussion of the merits of different indicators for specific purposes will be found in various parts of the book. 

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