Correction measuring molecular weight of LAS

The shortage of natural oils and fats during the Second World War has triggered the development of synthetic surfactants, mainly due to the better performance of the latter in hard water. However, the progressive replacement of soap by petrochemical-based surfactants began in the1950s.Linear alkyl benzenesulfonate (LAS) is considered the ideal “all-purpose” surfactant suitable for the widest range of detergent applications due to its optimized performances in terms of solubility, foaming, wetting, detergency, and compatibility with other detergent components.LAS results from the linear alkyl benzene (LAB) sulfonating reaction and its specific chemical composition, as well as application performance, depend on two main factors—the purity of the LAB raw material and sulfonating technique used. Molecular weight and C-chain distribution of LAS effect on quality characteristics in solubility, viscosity, purity, better performance and biodegradability [1].There are two methods for determination of Molecular weight: 1) INSO 14448 1st. edition [2], and 2) SANS 1170 edition 1.4 [3, 4]. In both of them extracted phase contain of desulfonated LAS and non-detergent organic matter, by this way measuring molecular weight and C-chain distribution isn’t accurate. In this study the accuracy of measuring molecular weight, purity and C-chain distribution of LAS was approved by removing of non-detergent organic matter.Two-step solvent extraction was used for measuring. In first step the sample of LAS was solved in ethanol-petroleum ether solvent mixture and non-detergent organic matter was removed of LAS. Then aqueous phase was used in desulfonation reaction and organic phase that collecting in this step was applied for investigating by Gas Chromatography (GC) instrument. Comparison of molecular weight, purity and C-chain distribution between LAB, aqueous phase desulfonation and direct LAS desulfonation proved our claim with Standard Deviation lower than 0.4. Finally the precision of the methods was calculated by F-Test (Fexp F crit).