Zinc Oxide Neutral
ZnO 81.39
ZnO 81.39
DEFINITION
Zinc Oxide Neutral, freshly ignited, contains NLT 95.0% and NMT 98.0% of ZnO.
IDENTIFICATION
• A.
When strongly heated, it assumes a yellow color that disappears on cooling.
• B. Identification Tests—General, Zinc 
191
191
Sample solution:
Dissolve in a slight excess of 3 N hydrochloric acid.
Acceptance criteria:
Meets the requirements
ASSAY
• Procedure
Sample:
1.5 g, freshly ignited
Analysis:
Dissolve the Sample and 2.5 g of ammonium chloride in 50.0 mL of 1 N sulfuric acid VS, with the aid of gentle heat if necessary. When dissolution is complete, add methyl orange TS, and titrate the excess sulfuric acid with 1 N sodium hydroxide VS. Each mL of 1 N sulfuric acid is equivalent to 40.69 mg of ZnO.
Acceptance criteria:
95.0%–98.0%
IMPURITIES
• Chloride and Sulfate, Sulfate 221:
A 0.1-g portion shows no more sulfate than corresponds to 2.3 mL of 0.020 N sulfuric acid (2.2%).
221:
A 0.1-g portion shows no more sulfate than corresponds to 2.3 mL of 0.020 N sulfuric acid (2.2%).
• Arsenic, Method I 211:
NMT 2 ppm
211:
NMT 2 ppm
• Lead
Sample solution:
Add 2 g to 20 mL of water, and stir well. Add 5 mL of glacial acetic acid, and warm on a steam bath until the solution is dissolved.
Analysis:
Add 5 drops of potassium chromate TS.
Acceptance criteria:
No turbidity or precipitate is produced.
• Mercury
Nitric acid solution 1:
Carefully add 50 mL of nitric acid to 450 mL of water, and mix.
Nitric acid solution 2:
Carefully add 10 mL of nitric acid to 490 mL of water, and mix.
Hydrochloric acid–nitric acid solution:
[Note—Prepare immediately before use. ] Concentrated hydrochloric acid and concentrated nitric acid (3:1)
Stannous sulfate solution:
[Note—The mixture is a suspension and should be stirred continuously during use. ] Add 25 g of stannous sulfate to 250 mL of 0.5 N sulfuric acid.
Sodium chloride–hydroxylamine sulfate solution:
120 mg/mL each of sodium chloride and hydroxylamine sulfate in water
Potassium permanganate solution:
50 mg/mL of potassium permanganate in water
Standard stock mercury solution:
[Note—Use of a commercially prepared mercury standard is recommended. ] 1.0 mg/mL of mercury from mercuric chloride in Nitric acid solution 1
Standard working mercury solution:
0.5 µg/mL of mercury in Nitric acid solution 2, from Standard stock mercury solution
Standard solutions:
Transfer 1-, 2-, 3-, and 4-mL aliquots of Standard working mercury solution to four separate 300-mL biological oxygen-demand (BOD) bottles. To each bottle add 5 mL of water and 5 mL of Hydrochloric acid–nitric acid solution. Heat the bottle for 2 min in a water bath at 95
. Cool, and add 50 mL of water and 15 mL of Potassium permanganate solution. Mix thoroughly, and place in a water bath for 30 min at 95. Cool, add 5 mL of Sodium chloride–hydroxylamine sulfate solution, and dilute with water to 200 mL. These solutions contain the equivalent of 2.5, 5, 7.5 and 10 ng/mL of mercury, respectively.
. Cool, and add 50 mL of water and 15 mL of Potassium permanganate solution. Mix thoroughly, and place in a water bath for 30 min at 95. Cool, add 5 mL of Sodium chloride–hydroxylamine sulfate solution, and dilute with water to 200 mL. These solutions contain the equivalent of 2.5, 5, 7.5 and 10 ng/mL of mercury, respectively.
Blank solution:
To a 300-mL BOD bottle add 5 mL of water and 5 mL of Hydrochloric acid–nitric acid solution. Heat the solution for 2 min in a water bath at 95. Cool, and add 50 mL of water and 15 mL of Potassium permanganate solution. Mix thoroughly, and place in a water bath for 30 min at 95. Cool, add 5 mL of Sodium chloride–hydroxylamine sulfate solution, and dilute with water to 200 mL.
. Cool, and add 50 mL of water and 15 mL of Potassium permanganate solution. Mix thoroughly, and place in a water bath for 30 min at 95. Cool, add 5 mL of Sodium chloride–hydroxylamine sulfate solution, and dilute with water to 200 mL.
Sample solution:
Transfer 2.0 g of Zinc Oxide Neutral into a 300-mL BOD bottle. To the bottle add 5 mL of water and 5 mL of Hydrochloric acid–nitric acid solution. Heat the sample in a water bath for 2 min at 95. Cool, and add 50 mL of water and 15 mL of Potassium permanganate solution. Mix thoroughly, and place in a water bath for 30 min at 95. Cool, add 5 mL of Sodium chloride–hydroxylamine sulfate solution, and dilute with water to 200 mL.
. Cool, and add 50 mL of water and 15 mL of Potassium permanganate solution. Mix thoroughly, and place in a water bath for 30 min at 95. Cool, add 5 mL of Sodium chloride–hydroxylamine sulfate solution, and dilute with water to 200 mL.
Mercury detection instrument and Aeration apparatus:
Proceed as directed for Mercury 261, Method IIa and Method IIb.
261, Method IIa and Method IIb.
Analysis:
Add 5 mL of Stannous sulfate solution to a Standard solution, and immediately insert the bottle into the Aeration apparatus. Measure the absorbance of the Standard solution. Repeat with the remaining Standard solutions and Sample solution. Perform a blank determination using Blank solution, and make any necessary corrections. Plot the absorbances of the Standard solutions versus concentrations, in µg/mL, and draw the straight line best fitting the plotted points. From the graph so obtained, determine the concentration, in ppm of mercury, in the Sample solution.
Acceptance criteria:
NMT 1 ppm
• Iron and Other Heavy Metals
Sample solution:
Use the solution from Carbonate and Color of Solution.
Analysis:
Cool 2 separate 5-mL aliquots of the Sample solution. Add potassium ferrocyanide TS to the first aliquot, and add sodium sulfide TS to the second aliquot.
Acceptance criteria:
White precipitates are formed in both aliquots.
• Magnesium Oxide
Nitric acid solution:
Carefully add 10 mL of concentrated nitric acid to 490 mL of water, and mix.
Standard solution:
[Note—Use of a commercially prepared magnesium–inductively coupled plasma standard solution is recommended. ] 25 µg/mL of magnesium in Nitric acid solution
Sample solution:
4 mg/mL of Zinc Oxide Neutral in Nitric acid solution
Blank:
Nitric acid solution
Instrumental conditions
Mode:
Inductively coupled plasma–atomic emission spectrometry
Analytical wavelength:
279.1 nm
RF power:
1.2 KW
Flow rate
Argon torch:
17 L/min
Argon nebulizer:
1.0 L/min
Argon auxiliary:
1.4 L/min
Analysis
Samples:
Standard solution, Sample solution, and Blank
Calculate the percentage of magnesium oxide in the portion of ZnO taken:
Result = (CU/CS) × (Mr1/Mr2) × 100
| CU | = | = concentration of magnesium in the Sample solution, determined from the instrument (µg/mL) |
| CS | = | = concentration of zinc oxide neutral in the Sample solution (µg/mL) |
| Mr1 | = | = molecular weight of magnesium oxide, 40.30 |
| Mr2 | = | = molecular weight of magnesium, 24.31 |
Acceptance criteria:
NMT 0.7%
• Loss on Ignition 733:
Weigh 1 g and ignite at 750 for 15 min: it loses NMT 5.0% of its weight.
733:
Weigh 1 g and ignite at 750 for 15 min: it loses NMT 5.0% of its weight.
SPECIFIC TESTS
• Alkalinity
Analysis:
Mix 1.0 g with 10 mL of hot water, and add two drops of phenolphthalein TS.
Acceptance criteria:
No color change occurs.
• Carbonate and Color of Solution
Analysis:
Mix 2.0 g with 10 mL of water, add 30 mL of 2 N sulfuric acid, and heat on a steam bath, with constant stirring.
Acceptance criteria:
No effervescence occurs and the resulting solution is clear and colorless. [Note—Use this solution in the test for Iron and Other Heavy Metals. ]
ADDITIONAL REQUIREMENTS
• Packaging and Storage:
Preserve in well-closed containers, and store at room temperature.
• Labeling:
Label it to indicate that it is for use in sunscreen preparations only.
Auxiliary Information—
Please check for your question in the FAQs before contacting USP.
| Topic/Question | Contact | Expert Committee |
|---|---|---|
| Monograph | Feiwen Mao, M.S.
Senior Scientific Liaison 1-301-816-8320 |
(SM32010) Monographs - Small Molecules 3 |
USP35–NF30 Page 5073
Pharmacopeial Forum: Volume No. 31(1) Page 80