Features peculiar to surfactant analysis

Mixtures of a few, or many, components that are chemically similar but show a spread of carbon or alkylene oxide chain lengths do not crystallise, and extracted solids are therefore often sticky or waxy. This is not of much practical consequence, but a difficulty due to the same root cause is that solvent extraction procedures may preferentially extract shorter or longer chains. An extreme instance is fatty alcohol ethoxylates. Petroleum ether extracts the parent alcohol and monoethoxylates from aqueous ethanol, but the solubility in petroleum ether decreases rapidly as the number of ethylene oxide groups increases, and triethoxylates and higher ethoxylates are extracted to only a small extent or not at all. 

Another consequence of surface activity is the fact that at low concentrations in aqueous solution, adsorption losses on glassware can be very substantial. At concentrations of lO mol/l and lower, particularly 

Yet another special feature is that in contact with ion-exchange resins, in an aqueous medium, there is a hydrophobic interaction between the hydrocarbon chains of surfactants and the organic matrix of the resin, which can cause substantial semipermanent retention on the column at the concentrations used in ion chromatography. This does not occur, however, in the largely non-aqueous media and at the concentrations used in the simple ion-exchange separation procedures described later. 

---