(Ph. Eur. monograph 0783)
Action and use
Antiseptic; antimicrobial preservative.
DEFINITION
Mixture of phenylmercuric nitrate (C6H5HgNO3; Mr 339.7) and phenylmercuric hydroxide (C6H5HgOH; Mr 294.7).
Content
62.5 per cent to 64.0 per cent of Hg (Ar 200.6) (dried substance).
CHARACTERS
Appearance
White or pale yellow powder.
Solubility
Very slightly soluble in water and in ethanol (96 per cent), slightly soluble in hot water. It dissolves in glycerol and in fatty oils.
IDENTIFICATION
A. To 5 mL of solution S (see Tests) add 8 mL of water R and 0.1 mL of sodium sulfide solution R. A white precipitate is formed that darkens slowly on heating.
B. To 1 mL of a saturated solution of the substance to be examined add 1 mL of dilute hydrochloric acid R. A white, flocculent precipitate is formed.
C. To 5 mL of solution S add 1 mL of dilute hydrochloric acid R, 2 mL of methylene chloride R and 0.2 mL of dithizone solution R. Shake. The lower layer is orange-yellow.
D. About 10 mg gives the reaction of nitrates (2.3.1).
TESTS
Solution S
To 0.1 g add 45 mL of water R and heat to boiling with shaking. Cool, filter and dilute to 50 mL with water R.
Appearance of solution
Solution S is colourless (2.2.2, Method II).
Inorganic mercuric compounds
Maximum 0.1 per cent.
To 10 mL of solution S add 2 mL of potassium iodide solution R and 3 mL of dilute hydrochloric acid R. Filter. The filtrate is colourless. Wash the precipitate with 2 mL of water R. Combine the filtrate and washings, add 2 mL of dilute sodium hydroxide solution R and dilute to 20 mL with water R. 12 mL of the solution complies with test A for heavy metals (2.4.8).
Prepare the reference solution using lead standard solution (1 ppm Pb) R.
Loss on drying (2.2.32)
Maximum 1.0 per cent, determined on 1.000 g by drying in vacuo for 24 h.
ASSAY
Dissolve 0.150 g in a mixture of 10 mL of dilute nitric acid R and 90 mL of water R, heating to boiling. Cool to 15-20 °C.
Titrate with 0.1 M ammonium thiocyanate using 2 mL of ferric ammonium sulfate solution R2 as indicator, until a persistent reddish-yellow colour is obtained. Carry out a blank titration.
1 mL of 0.1 M ammonium thiocyanate is equivalent to 20.06 mg of Hg.
STORAGE
Protected from light.
