Thin-layer chromatography nonionics

Nonionic surfactants, including EO-PO block copolymers, may be readily separated from anionic surfactants by a simple batch ion exchange method [21] analytical separation of EO-PO copolymers from other nonionic surfactants is possible by thin-layer chromatography (TLC) [22,23] and paper chromatography [24], and EO-PO copolymers may themselves be separated into narrow molecular weight fractions on a preparative scale by gel permeation chromatography (GPC) [25]. 

Separation is carried out using various techniques, depending on the nature of the compounds. For nonionic species the solubilities of the compounds are generally low and similar, and it has been necessary to use either fractionation by continuous extraction with low boiling solvents (36) or thin-layer chromatography (58, 60). The first method has been used with air-sensitive compounds, whereas the second has been applied only to air-stable substances. In both cases, it is possible to separate only limited amounts of compounds, whose characterization is, therefore, carried out using particular techniques such as mass spectroscopy (58-60). 

Thin layer chromatography is a rapid and inexpensive method that is often used to separate surfactants into classes, i.e. to separate ionic surfactants from nonionic ones. Typical stationary phases used in TLC are usually unmodified or modified (e.g. hydrophobized) silica or alumina. Quantitative analysis using TLC is based on one s ability to isolate the spot on the TLC plate and determine the concentration of active material in it. For example, the surfactant can be extracted into an appropriate solvent, and then analyzed by a suitable technique. Alternatively, one can develop the chromatogram with the suitable reagent to produce colored compound and then analyze the colored spot with optical densitometer. 

IR spectroscopy is used for the qualitative identihcation of surfactants and for differentiating between them and nonsurfactant compounds. Prior to IR spectroscopy, however, separation of the organic compound complex into different fractions, performed by, e.g., the use of thin-layer chromatography, is required to obtain meaningful spectra. °" ° By comparing the IR spectra of the isolated fractions with IR spectra of standard compounds with regard to characteristic bands, the qualitative determination of surfactants in environmental samples is possible. The method is equally applicable to anionic, ° nonionic, °" and cationic surfactants.The prerequisite for a clear identification of surfactants, however, is the availability of suitable standards. Moreover, considerable experience and knowledge are needed to interpret IR spectra of environmental samples. 

The Michelsen method [68] proceeds in a similar manner, but the nonionic surfactants are determined by means of thin-layer chromatography. 

Essquena, J., Solans, C. Influence of the HLB parameter of nonionic surfactants on normal and reversed-phase thin layer chromatography. Colloids Surf. A 2001, 789(1-3), 85-92. 

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