Sodium Lauryl Sulfate

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

Sodium Lauryl Sulfate is a mixture of sodium alkyl sulfates consisting chiefly of sodium lauryl sulfate (C₁₂H₂₅NaO₄S). It contains NLT 85.0% of sodium alkyl sulfates calculated as sodium lauryl sulfate (C₁₂H₂₅NaO₄S).

2 IDENTIFICATION

Change to read:

A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197A or 197K (NF 1-May-2021)

B. Sodium

Potassium pyroantimonate solution: To 2 g of potassium pyroantimonate add 100 mL of water. Boil the solution for about 5 min, cool quickly, and add 10 mL of a solution of potassium hydroxide (3 in 20). Allow to stand for 24 h, and filter.

Sample: 2.5 g

Analysis: Place the Sample in a silica or platinum crucible, and add 2 mL of 10 N sulfuric acid. Heat on a water bath, then cautiously raise the temperature progressively over an open flame. Ignite, preferably in a mufle furnace, at 600 ± 25°. Continue heating until all black particles have disappeared. Cool, add a few drops of 2 N sulfuric acid, and heat and ignite as above. Add a few drops of ammonium carbonate TS, evaporate to dryness, and ignite as above. Cool, dissolve the residue in 50 mL of water, and mix. To a 2-mL portion of this solution, add 4 mL of Potassium pyroantimonate solution. If necessary, rub the inside of the test tube with a glass rod.

Acceptance criteria: A white, crystalline precipitate is formed.

C. Sulfate

Sample: Solution (1 in 10)

Analysis: After acidification with hydrochloric acid and boiling for 20 min, no precipitate is formed. Add barium chloride TS; a white precipitate is produced.

Acceptance criteria: Meets the requirements

Delete the following:

D.

Sample: 0.1 g

Analysis: Dissolve the Sample in 10 mL of water and shake.

Acceptance criteria: A copious foam is formed. (NF 1-May-2021)

Delete the following:

E.

Sample: Solution prepared for Identification D

Analysis: To 0.1 mL of the Sample, add 0.1 mL of a 1-g/L solution of methylene blue and 2 mL of diluted sulfuric acid. Add 2 mL of methylene chloride and shake.

Acceptance criteria: An intense blue color develops in the methylene chloride layer.(NF 1-May-2021)

3 ASSAY

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Content of Sodium Alkyl Sulfates

Dimidium bromide–sulfan blue mixed solution: Dissolve separately 0.5 g of dimidium bromide and 0.25 g of sulfan blue in 30 mL of a hot solution of 10% Ethanol in water, combine these solutions, and dilute with 10% ethanol to 250 mL. Mix 20 mL of this solution with 20 mL of a 14.0% (v/v) solution of sulfuric acid previously diluted with about 250 mL of water, and dilute with water to 500 mL. (NF 1-May-2021)

Sample: 1.15 g (NF 1-May-2021) of Sodium Lauryl Sulfate

Titrimetric system

(See Titrimetry 〈541〉.)

Mode: Direct titration

Titrant: 0.004 M benzethonium chloride VS

Endpoint detection: Visual

Analysis: Dissolve the Sample in water, warming if necessary, and dilute with water to exactly 1000.0 mL. Mix 20.0 mL of the solution with 15 mL of methylene chloride and 10 mL of Dimidium bromide–sulfan blue mixed solution. (NF 1-May-2021) Titrate with Titrant, shaking vigorously and allowing the layers to separate before each addition, until the pink color of the methylene chloride layer is completely discharged and a greyish-blue color is obtained. (NF 1-May-2021) One milliliter of Titrant is equivalent to 1.154 mg of sodium alkyl sulfates, calculated as sodium lauryl sulfate (C₁₂H₂₅NaO₄S).

Acceptance criteria: NLT 85.0%, calculated as sodium lauryl sulfate (C H NaO S)

4 IMPURITIES

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Sodium Chloride

Fluorescein Sodium solution: Dissolve 0.2 g of fluorescein sodium in water to 100 mL.

Dilute nitric acid: Dilute 105 mL of nitric acid with water to 1000 mL.

Sample solution: 100 mg/mL of Sodium Lauryl Sulfate in water

Analysis: Neutralize 50 mL of Sample solution with Dilute nitric acid, using litmus paper as the indicator, if necessary. Add exactly 5.0 mL of 0.1 N sodium chloride and titrate, under vigorous stirring (to disperse silver chloride), (NF 1-May-2021) with 0.1 N silver nitrate VS (indicator: 2 drops of Fluorescein sodium solution) to the first appearance of turbidity with solution color change from yellow-green to orange through yellow. Perform a blank determination, and make any necessary correction. Each milliliter of 0.1 N silver nitrate is equivalent to 5.844 mg of sodium chloride.

Acceptance criteria: The combined content of sodium chloride and sodium sulfate is NMT 8.0%.

Change to read:

Sodium Sulfate

Sample solution: 100 mg/mL of Sodium Lauryl Sulfate in water

Analysis: To 10 mL of Sample solution, add 100 mL of alcohol and heat at a temperature just below the boiling point for 2 h. Pass through a glass or porcelain (NF 1-May-2021) filter (pore size equivalent to 4–10 μm) (NF 1-May-2021) while hot, and wash with 100 mL of boiling alcohol. Dissolve the precipitate by washing with 150 mL of water, collecting the washings in a beaker. Add 10 mL of diluted hydrochloric acid, heat to boiling, add 25 mL of barium chloride TS, and allow to stand overnight. Collect the precipitate by ltration through a filter (maximum pore size of 16 μm) (NF 1-May-2021) and wash with water until the last washing shows no opalescence with 0.1 N silver nitrate VS (NF 1-May-2021) . Dry the precipitate, ignite to constant mass between 500° and 600° by raising the temperature gradually, and weigh as barium sulfate (BaSO₄; 233.39).

Amount (mg) of sodium sulfate (Na₂SO₄) = amount (mg) of barium sulfate (BaSO₄) × 0.6086

Acceptance criteria: The combined content of sodium chloride and sodium sulfate is NMT 8.0%.

5 SPECIFIC TESTS

Alkalinity

Sample solution: Dissolve 1.0 g in 100 mL of water, add 0.1 mL of phenol red TS, and titrate with 0.10 N hydrochloric acid.

Acceptance criteria: NMT 0.5 mL for neutralization

Total Alcohols: Transfer 5 g to an 800-mL Kjeldahl flask, and add 150 mL of water, 50 mL of hydrochloric acid, and a few boiling chips. Attach a reflux condenser to the Kjeldahl flask, heat carefully to avoid excessive frothing, and boil for 4 h. Cool the flask, rinse the condenser with ether, collecting the ether in the flask, and transfer the contents to a 500-mL separator, rinsing the flask twice with ether and adding the washings to the separator. Extract the solution with two 75-mL portions of ether, evaporate the combined ether extracts in a tared beaker on a steam bath, dry the residue at 105° for 30 min, cool, and weigh.

Acceptance criteria: The residue represents the total alcohols and is NLT 59.0% of the weight of Sodium Lauryl Sulfate taken.

Unsulfated Alcohols

Sample solution: Dissolve 10 g in 100 mL of water, and add 100 mL of alcohol.

Analysis: Transfer the solution to a separator, and extract with three 50-mL portions of petroleum ether. If an emulsion forms, sodium chloride may be added to promote separation of the two layers. Wash the combined petroleum ether extracts with three 50-mL portions of water, and dry with anhydrous sodium sulfate. Filter the petroleum ether extract into a tared beaker. Evaporate on a water bath until the odor of petroleum ether no longer is perceptible, dry the residue at 105° for 30 min, cool, and weigh.

Acceptance criteria: The weight of the residue is NMT 4.0% of the weight of Sodium Lauryl Sulfate taken.

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers.

USP Reference Standards 〈11〉

USP Sodium Lauryl Sulfate RS