Sulfate Content in Sodium Lauryl Ether Sulfate

The application gives the method for determination of Sulfate content in sodium lauryl ether sulfate (SLES). It is determined by precipitation titration using lead nitrate Pb(NO₃)₂ as a titrant to form insoluble PbSO₄ in a non-aqueous solution. The titration is monitored with a lead selective electrode with solid-state membrane.

Background:

Sodium lauryl ether sulfate (SLES), is one of the most important anionic surfactants that has found broad use in detergents and cosmetics. Depending on the chain length of the ethoxy (EO) unit i.e. CH₃-CH₂-O- in its molecular structure, SLES may be a more or less viscous liquid.

On an industrial scale, SLES is mainly produced by ethoxylation of the long alkyl chain alcohol n-dodecanol. This step is first followed by the sulfation of the ethoxylate product, and then by the final neutralization to obtain the corresponding sodium salt.

Reaction:

R(OC₂H₄)_nOH + SO₃ ----> R(OC₂H₄)_nOSO₃H

R(OC₂H₄)_nOSO₃H +NaOH ----> R(OC₂H₄)_nSO₃Na  + H₂O

Thus, sulfate content SO₄^2- is monitored at the end of production for quality control.