Introduction
Sodium Lauryl Sulphate (SLS) is a widely used pharmaceutical and cosmetic ingredient. It works mainly as a surfactant, which means it helps lower surface tension and allows liquids to mix better. These notes explain its preparation, purity tests, assay, and uses in simple language suitable for Pharm.D students.
Formula
NaC12H25SO4
Preparation
Sodium Lauryl Sulphate is prepared by sulphating long-chain fatty alcohols. These long-chain alcohols are obtained from coconut oil through high-pressure hydrogenation using a copper–chromium oxide catalyst. After sulphation, the product is neutralized with an alkali to produce the sodium salt known as SLS.
Tests for Purity
- Alkalinity: Less than 0.5 ml of 0.1M HCl
- Non-esterified alcohol: Less than 4%
- Sodium chloride & sodium sulphate: Less than 8% w/w
Assay
About 1.15 g of the sample is dissolved in water to make a 1000 ml solution. The solution is warmed if needed, then 15 ml of chloroform, 10 ml of dilute sulphuric acid, and dimethyl oracet blue indicator are added. The mixture is titrated with 0.004M benzethonium chloride until the chloroform layer turns a permanent clear green. Each 1 ml of 0.004M benzethonium chloride corresponds to 0.00115 g of Sodium Lauryl Sulphate.
An alternative method is gravimetric analysis using the same conversion factor.
Uses
- Used as a pharmaceutical aid.
- Acts as a surfactant to help mixing of ingredients.
- Used as an emulsifier in various formulations.
Detailed Notes:
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PATH: PHARMD/PHARMD NOTES/ PHARMD FIRST YEAR NOTES/ ORGANIC CHEMISTRY/ PHARMACEUTICAL ORGANIC CHEMISTRY/ SODIUM LAURYL SULPHATE.