Purified Cotton

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION 

Purified Cotton is the hair of the seed of cultivated varieties of Gossypium hirsutum L. or other species of Gossypium (Family Malvaceae), freed from adhering impurities, deprived of fatty matter, bleached, and sterilized in its nal container. 

2 IDENTIFICATION 

Add the following: 

Auxiliary Packaging Components 〈670〉, Pharmaceutical Coil, Cotton Pharmaceutical Coil: Meets the requirements Add the following: 

Fluorescence: No intense blue with UV

3 IMPURITIES 

Residue on Ignition 〈281〉 

Sample: 5 g of Purified Cotton 

Analysis: Place the Sample in a porcelain or platinum dish, and moisten with 2 N sulfuric acid. Gently heat the cotton until it is charred, then ignite more strongly until the carbon is completely consumed. 

Acceptance criteria: NMT 0.20% of residue remains. 

Organic Impurities: Fatty Matter 

Sample: 10 ± 0.01 g of Purified Cotton 

Analysis: Pack the Sample in a Soxhlet extractor provided with a tared receiver, and extract with ether for 5 h at a rate such that the ether siphons over NLT 4 times/h. The ether solution in the flask shows no trace of blue, green, or brownish color. Evaporate the extract to dryness, and dry at 105° for 1 h. 

Acceptance criteria: The weight of the residue is NMT 70 mg (0.7%). 

4 SPECIFIC TESTS 

Acidity or Alkalinity 

Sample: 10 g of Purified Cotton 

Analysis: Thoroughly saturate the Sample with 100 mL of recently boiled and cooled water, then with the aid of a glass rod, press out two 25- mL portions of the water into white porcelain dishes. To one portion add 3 drops of phenolphthalein TS, and to the other portion add 1 drop of methyl orange TS. 

Acceptance criteria: No pink color develops in either portion. 

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Loss on Drying 

Auxiliary Packaging Components 〈670〉, Pharmaceutical Coil, Cotton Pharmaceutical Coil: Meets the requirements  Sterility Tests 〈71〉: Meets the requirements 

Water-Soluble Substances 

Sample: 10 g of Purified Cotton 

Analysis: Place the Sample in a beaker containing 1000 mL of water and boil gently for 30 min, adding water as required to maintain the volume. Pour the water through a funnel into another vessel, and press out the excess water from the cotton with a glass rod. Wash the cotton in the funnel with two 250-mL portions of boiling water, pressing the cotton after each washing. Filter the combined extract and washings, and wash the filter thoroughly with hot water. Evaporate the combined extract and washings to a small volume, transfer to a tared porcelain or platinum dish, evaporate to dryness, and dry the residue at 105° to constant weight. 

Acceptance criteria: The residue weighs NMT 35 mg (0.35%). 

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Fiber Length 

Sample: Remove Purified Cotton from its wrappings, and condition it for NLT 4 h in a standard atmosphere of 65 ± 2% relative humidity at 21 ± 1° before determining the fiber length. 

Analysis: Determine the fiber length using a suitable method. 

Acceptance criteria: NMT 10% of the fibers by weight are 6.25 mm or less in length.  

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Absorbency 

Sample: Remove Purified Cotton from its wrappings, and condition it for NLT 4 h in a standard atmosphere of 65 ± 2% relative humidity at 21 ± 1° before determining the absorbency. 

Analysis: Prepare a test basket, weighing NMT 3 g, from copper wire approximately 0.4 mm in diameter (No. 26, B. & S. gauge) in the form of a cylinder approximately 5 cm in diameter and 8 cm deep, with spaces of about 2 cm between the wires. Take portions of cotton weighing 1 ± 0.05 g from ve different parts of the package by pulling, not cutting, the specimens. Combine the portions in the basket and weigh. Hold the basket on its side approximately 12 mm above the surface of water at 25 ± 1° and drop it into the water. Determine, preferably by use of a stopwatch, the time in seconds required for complete submersion. Remove the basket from the water, allow it to drain for 10 s in the same horizontal position, then place it immediately in a tared, covered vessel, and weigh, deducting the weight of the test basket and of the cotton to determine the weight of water absorbed. 

Acceptance criteria: Submersion is complete in 10 s at a temperature of 25°, and the cotton retains NLT 24 times its weight of water. (USP 1- Dec-2020) 

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Cotton 〈691〉, Fiber Length and Absorbency Test: Remove it from its wrappings, and condition it for NLT 4 h in a standard atmosphere of 65 ± 2% relative humidity at 21 ± 1.1° (70 ± 2°F), before determining the Fiber length and Absorbency. 

Fiber length 

Analysis: Determine the fiber length of Purified Cotton as directed under Cotton 〈691〉, Fiber Length. 

Acceptance criteria: NLT 60% of the bers by weight are 12.5 mm or greater in length, and NMT 10% of the bers by weight are 6.25 mm or less in length. 

Absorbency 

Analysis: Proceed as directed under Cotton 〈691〉, Absorbency Test. 

Acceptance criteria: Submersion is complete in 10 s at a temperature of 25°, and the cotton retains NLT 24 times its weight of water.  

Dyes 

Sample: 10 g of Purified Cotton 

Analysis: Pack the Sample in a narrow percolator, and extract slowly with alcohol until the percolate measures 50 mL. Acceptance criteria: When observed downward through a column 20 cm in depth, the percolate may show a yellowish color but neither a blue nor a green tint. 

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Other Foreign Matter: The samples  of Purified Cotton taken for the determination of fiber length in the test for Fiber Length contain no oil stains or metallic particles on visual inspection.  

5 ADDITIONAL REQUIREMENTS 

Packaging and Storage: Package Purified Cotton in rolls of NMT 500 g of a continuous lap, with a lightweight paper running under the entire lap, the paper being of such width that it may be folded over the edges of the lap to a distance of at least 25 mm, the two together being tightly and evenly rolled, enclosed, and sealed in a well-closed container. It also may be packaged in other types of containers if these are so constructed that the sterility of the product is maintained. 

Labeling: Its label bears a statement to the effect that the sterility cannot be guaranteed if the package bears evidence of damage or if the package has been opened previously.