Sodium Lauryl Sulfate

Sodium Dodecyl Sulfate; Sodium Lauryl Sulphate

(Sodium Laurilsulfate, Ph Eur monograph 0098)

Anionic emulsifying agent.

Ph Eur

Mixture of sodium alkyl sulfates consisting chiefly of sodium dodecyl sulfate (C₁₂H₂₅NaO₄S; M_r 288.4).

• — sodium alkyl sulfates: minimum 85.0 per cent, expressed as C₁₂H₂₅NaO₄S.

White or pale yellow, powder or crystals.

Freely soluble in water giving an opalescent solution, partly soluble in ethanol (96 per cent).

A. Dissolve 0.1 g in 10 mL of water R and shake. A copious foam is formed.

B. To 0.1 mL of the solution prepared for identification test A, add 0.1 mL of a 1 g/L solution of methylene blue R and 2 mL of dilute sulfuric acid R. Add 2 mL of methylene chloride R and shake. An intense blue colour develops in the methylene chloride layer.

C. Mix about 10 mg with 10 mL of anhydrous ethanol R. Heat to boiling on a water-bath, shaking frequently. Filter immediately and evaporate the ethanol. Dissolve the residue in 8 mL of water R, add 3 mL of dilute hydrochloric acid R, evaporate the solution to half its volume and allow to cool. Separate the congealed fatty alcohols by filtration. To the filtrate add 1 mL of barium chloride solution R1. A white, crystalline precipitate is formed.

D. Ignite 0.5 g. The residue gives reaction (a) of sodium (2.3.1).

Dissolve 1.0 g in 100 mL of carbon dioxide-free water R and add 0.1 mL of phenol red solution R. Not more than 0.5 mL of 0.1 M hydrochloric acid is required to change the colour of the indicator.

Maximum 4 per cent.

Dissolve 10 g in 100 mL of water R, add 100 mL of ethanol (96 per cent) R and shake the solution with 3 quantities, each of 50 mL, of pentane R, adding sodium chloride R, if necessary, to promote separation of the 2 layers. Wash the combined organic layers with 3 quantities, each of 50 mL, of water R, dry over anhydrous sodium sulfate R, filter and evaporate on a water-bath until the solvent has evaporated. Heat the residue at 105 °C for 15 min and cool. The residue weighs a maximum of 0.4 g.

Maximum 8.0 per cent for the total percentage content.

Dissolve 5.00 g in 50 mL of water R, add dilute nitric acid R dropwise until the solution is neutral to blue litmus paper R, add 2 mL of potassium chromate solution R and titrate with 0.1 M silver nitrate.

1 mL of 0.1 M silver nitrate is equivalent to 5.844 mg of NaCl.

Dissolve 0.500 g in 20 mL of water R, warming gently if necessary, then add 1 mL of a 0.5 g/L solution of dithizone R1 in acetone R. If the solution is red, add 1 M nitric acid, dropwise, until the solution becomes bluish-green. Add 2.0 mL of dichloroacetic acid solution R and 80 mL of acetone R. Titrate with 0.01 M lead nitrate until a persistent violet-red or orange-red colour is obtained. Carry out a blank titration.

1 mL of 0.01 M lead nitrate is equivalent to 1.420 mg of Na₂SO₄.

Dissolve 1.15 g in water R, warming if necessary, and dilute to 1000.0 mL with the same solvent. To 20.0 mL of the solution add 15 mL of chloroform R and 10 mL of dimidium bromide-sulfan blue mixed solution R. Titrate with 0.004 M benzethonium chloride, shaking vigorously and allowing the layers to separate before each addition, until the pink colour of the chloroform layer is completely discharged and a greyish-blue colour is obtained.

1 mL of 0.004 M benzethonium chloride is equivalent to 1.154 mg of sodium alkyl sulfates, expressed as C₁₂H₂₅NaO₄S.

Ph Eur