Title: Raw Material Test Method

Material            : Zinc Oxide

Generic Name              :           Zinc Oxide

Empirical Formula       :           ZnO                                    

Molecular weight         :           81.39

Reas Also Raw Material Test Method - Zinc Sulfate Monohydrate

Method of Analysis:

1.     Appearance

Soft, white or faintly yellowish-white, amorphous powder, free from gritty particles.

2.     Solubility

Practically insoluble in water and in ethanol (96 per cent). It dissolves in dilute mineral acids.

3.     Identification

A.     It becomes yellow when strongly heated; the yellow colour disappears on cooling.

B.     It gives the reactions of Zinc.

Dissolve 0.1 g in 1.5 ml of dilute hydrochloric acid and dilute to 5 ml with water. Add 0.2 ml of strong sodium hydroxide solution. A white precipitate is formed. Add a further 2 ml of strong sodium hydroxide solution. The precipitate dissolves. Add 10 ml of ammonium chloride solution. The solution remains clear. Add 0.1 ml of sodium sulphide solution. A flocculent white precipitate is formed.

4.     Alkalinity

Shake 1.0 g with 10 ml of boiling water. Add 0.1 ml of phenolphthalein solution 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.

5.     Carbonates and substances insoluble in acids

Clarity test

Dissolve 1.0 g in 15 ml of dilute hydrochloric acid. It dissolves without effervescence and the solution is not more opalescent than reference suspension II and is colourless.

Visual method

Using identical test-tubes of colourless, transparent, neutral glass with a flat base and an internal diameter of 15-25 mm, compare the liquid to be examined with a reference suspension freshly prepared as described below, the depth of the layer being 40 mm. Compare the solutions in diffused daylight 5 min after preparation of the reference suspension, viewing vertically against a black background. The diffusion of light must be such that reference suspension I can readily be distinguished from water, and that reference suspension II can readily be distinguished from reference suspension I.

A liquid is considered clear if its opalescence is not more pronounced than that of reference suspension II.

Hydrazine sulphate solution 

Dissolve 1.0 g of hydrazine sulphate in water and dilute to 100.0 ml with the same solvent. Allow to stand for 4-6 h.

Hexamethylenetetramine solution 

In a 100 ml ground-glass-stoppered flask, dissolve 2.5 g of hexamethylenetetramine in 25.0 ml of water.

Primary opalescent suspension (formazin suspension) 

To the hexamethylenetetramine solution in the flask add 25.0 ml of the hydrazine sulphate solution. Mix and allow to stand for 24 h. This suspension is stable for 2 months, provided it is stored in a glass container free from surface defects. The suspension must not adhere to the glass and must be well mixed before use.

Standard of opalescence 

Dilute 15.0 ml of the primary opalescent suspension to 1000.0 ml with water. This suspension is freshly prepared and may be stored for up to 24 h.

Reference suspensions 

Prepare the reference suspension II according to the following. Mix and shake before use.

Turbidity standard 

The formazin suspension prepared by mixing equal volumes of the hydrazine sulphate solution and the hexamethylenetetramine solution is defined as a 4000 NTU (nephelometric turbidity units) primary reference standard. Reference suspension II has values of 6 NTU.

Test of Colour of solution

      Check color of solution against dilute Hydrochloric acid. The sample solution is not more intensed than blank (Dilute Hydrochloric acid). 

6.     Arsenic

Instrumentation

The apparatus consists of a 100 ml conical flask closed with a ground-glass stopper through which passes a glass tube about 200 mm long and of internal diameter 5 mm. The lower part of the tube is drawn to an internal diameter of 1.0 mm, and 15 mm from its tip is a lateral orifice 2 mm to 3 mm in diameter. When the tube is in position in the stopper, the lateral orifice should be at least 3 mm below the lower surface of the stopper. The upper end of the tube has a perfectly flat, ground surface at right angles to the axis of the tube. A second glass tube of the same internal diameter and 30 mm long, with a similar flat ground surface, is placed in contact with the first, and is held in position by two spiral springs. Into the lower tube insert 50 mg to 60 mg of lead acetate cotton, loosely packed, or a small plug of cotton and a rolled piece of lead acetate paper weighing 50 mg to 60 mg.  Between the flat surfaces of the tubes place a disc or a small square of mercuric bromide paper R large enough to cover the orifice of the tube (15 mm × 15 mm).

Procedure

In the conical flask dissolve 0.2 g sample in 25 ml of water. Add 15 ml of hydrochloric acid, 0.1 ml of stannous chloride solution and 5 ml of potassium iodide solution, allow standing for 15 min and introducing 5 g of activated zinc. Assemble the two parts of the apparatus immediately and  immerse the flask in a bath of water at a temperature such that a uniform evolution of  gas is maintained. Prepare a standard in the same manner, using 1 ml of arsenic standard solution (1 ppm As), diluted to 25 ml with water.

After not less than 2 h the stain produced on the mercuric bromide paper in the test  is not more intense than that in the standard.

Limit: NMT 5.00 ppm

7.     Cadmium

Atomic absorption spectrometry

Test solution 

Dissolve 2.0 g in 14 ml of a mixture of equal volumes of water and  cadmium- and lead-free nitric acid R, boil for 1 min, cool and dilute to 100.0 ml with  water.

Reference solutions

Prepare the reference solutions using cadmium standard  solution (0.1 per cent Cd) and diluting with a 3.5 per cent V/V solution of cadmium-  and lead-free nitric acid.

Source  Cadmium hollow-cathode lamp.

Wavelength 228.8 nm.

Atomisation device Air-acetylene or air-propane flame.  

Limit: NMT 10.0 ppm.

8.     Iron

Dissolve 50 mg of sample in diluted hydrochloric acid and dilute to 10 ml with the same solvent. Add 2 ml of a 200-g/l solution of citric acid and 0.1 ml of thioglycollic acid. Mix, make alkaline with ammonia and dilute to 20 ml with water. Prepare a standard in the same manner, using 10 ml of iron standard solution (1 ppm Fe). After 5 min, any pink colour in the test solution is not more intense than that in the standard.

Limit: NMT 200.0 ppm.

9.     Lead

Atomic absorption spectrometry

Test solution

Dissolve 5.0 g in 24 ml of a mixture of equal volumes of water R and  cadmium- and lead-free nitric acid R, boil for 1 min, cool and dilute to 100.0 ml with  water R.

Reference solutions

Prepare the reference solutions using lead standard solution (0.1 per cent Pb) R and diluting with a 3.5 per cent V/V solution of cadmium- and lead-free nitric acid R.

Source  Lead hollow-cathode lamp.

Wavelength 283.3 nm; 217.0 nm may be used depending on the apparatus.

Atomisation device Air-acetylene flame.

Limit: NMT 50.0 ppm.

10.  Loss on ignition

Loss on ignition is determined on 1.00 g by ignition to constant mass at 500 ± 50 °C.

Calculation:   

 Where,

         W1 = weight of empty crucible

      W2 = weight of crucible along with sample

      W3 = weight of crucible along with residue

Limit: NMT 1.0 %

11.  Assay

Dissolve 0.150 g in 10 ml of dilute acetic acid. Then introduce it into a 500 ml conical flask and dilute to 200 ml with water. Add about 50 mg of xylenol orange triturate and hexamethylenetetramine until the solution becomes violet-pink. Add 2 g of hexamethylenetetramine in excess. Titrate with 0.1 M sodium edetate until the violet-pink colour changes to yellow.

1 ml of 0.1 M sodium edetate is equivalent to 8.14 mg of ZnO.

Calculation

      Limit: (99.0 – 100.50) %

Alternative Method (Reference USP)

Dissolve about 1.5 g of freshly ignited Zinc Oxide, accurately weighed and 2.5 g of ammonium chloride in 50 ml of 1 N sulfuric acid VS with the aid of gently heat, if necessary when the solution is complete, add methyl orange TS and titrate the excess sulfuric acid with 1 N sodium hydroxide.

Each ml of 1 N sulfuric acid is equivalent to 40.69 mg of ZnO.

Calculation

      Limit: (99.0 – 100.50) %

Alternative Method (Ion Chromatographic)

ASSAY

PROCEDURE

Proceed as directed in Zinc Determination (591), Ion Chromatographic Method.

Diluent: 0.2% (w/v) hydrochloric acid

Standard solution: 20 μg/mL of USP Zinc Oxide RS in Diluent, prepared as directed in the chapter

Sample solution: 20 μg/mL of Zinc Oxide from the freshly ignited Zinc Oxide in Diluent, prepared as directed in the Standard solution

Analysis

Samples: Standard solution and Sample solution Calculate the percentage of zinc oxide (ZnO) in the portion of Zinc Oxide taken:

Result = (ru/rs) × (Cs/Cu) × 100

ru = peak response of zinc from the Sample solution

rs = peak response of zinc from the Standard solution

Cs = concentration of USP Zinc Oxide RS in the Standard solution (μg/mL)

Cu = concentration of Zinc Oxide in the Sample solution (μg/mL)