Polyoxyethylene alkyl ether nonionic surfactants: physicochemical properties and use for cholesterol determination in food

Polyoxyethylene alkyl ethers, CnEm, are nonionic surfactants made of an alkyl chain with n methylene groups and a hydrophilic part with m oxyethylene units. CnEm nonionic surfactants are very useful in chemical analysis. The commercially available products are often a mixture of several CnEm molecules with different m values. Pure CnEm surfactants are now available. The physicochemical parameters: critical micelle concentration (c.m.c.), molar volume, density, cloud-point temperature and hydrophile–lipophile balance value for pure CnEm surfactants were collected from the literature. Regression analyses were carried out on the data. They showed that strong correlations existed between the structure of the molecule (n and m values) and its physicochemical properties. General equations linking the c.m.c., molar volume, density and cloud-point temperature of the CnEm surfactants and their structure (n and m values) are proposed and discussed. The use of these surfactants in chemical analysis is illustrated by the determination of cholesterol in egg yolk. Cholesterol was separated from the bulk yolk by cloud-point extraction using the C12E10 surfactant. It was quantitated using micellar liquid chromatography. The C12E23 surfactant was used to prepare the micellar mobile phase that allowed the separation of cholesterol and the use of an enzymatic detector.