Edition: BP 2025 (Ph. Eur. 11.6 update)
Action and use
Mild astringent.
Preparations
Zinc Cream
Coal Tar and Zinc Ointment
Zinc Ointment
Zinc and Castor Oil Ointment Compound
Zinc Paste
Zinc and Salicylic Acid Paste
Zinc and Coal Tar Paste
DEFINITION
Content
99.0 per cent to 100.5 per cent (ignited substance).
CHARACTERS
Appearance
Soft, white or faintly yellowish-white, amorphous powder, free from gritty particles.
Solubility
Practically insoluble in water and in ethanol (96 per cent). It dissolves in dilute mineral acids.
IDENTIFICATION
A. It becomes yellow when strongly heated; the yellow colour disappears on cooling.
B. Dissolve 0.1 g in 1.5 mL of dilute hydrochloric acid R and dilute to 5 mL with water R. The solution gives the reaction of zinc (2.3.1).
TESTS
Alkalinity
Shake 1.0 g with 10 mL of boiling water R. Add 0.1 mL of phenolphthalein solution R and filter. If the filtrate is red, not more than 0.3 mL of 0.1 M hydrochloric acid is required to change the colour of the indicator.
Carbonates and substances insoluble in acids
Dissolve 1.0 g in 15 mL of dilute hydrochloric acid R. It dissolves without effervescence and the solution is not more opalescent than reference suspension II (2.2.1) and is colourless (2.2.2, Method II).
Elemental impurities
Any method that fulfils the requirements of general chapter 2.4.20. Determination of elemental impurities may be used.
| Element | Maximum content (ppm) |
| Cadmium
Lead Thallium |
5
10 5 |
Iron (2.4.9)
Maximum 200 ppm.
Dissolve 50 mg in 1 mL of dilute hydrochloric acid R and dilute to 10 mL with water R. Use 0.5 mL of thioglycollic acid R in this test.
Loss on ignition
Maximum 1.0 per cent, determined on 1.00 g by ignition to constant mass at 500 ± 50 °C.
ASSAY
Dissolve 0.150 g in 10 mL of dilute acetic acid R. Carry out the complexometric titration of zinc (2.5.11). 1 mL of 0.1 M sodium edetate is equivalent to 8.14 mg of ZnO.
