Classification and Analysis of Surfactants

Surfactants are classified according to the nature of the polar (hydrophilic) part of the molecule, as illustrated in Table 3.3. Typically the molar masses range from a few hundreds to several thousands of g/mol. In depth discussions of surfactant structure and chemistry can be found in Refs. [32,160-162]. A recent review is given by Schramm et al. [163], A good discussion of the chemistry of commercially available surfactants is given by Myers [31]. Several reviews are available on the toxicity and persistence of surfactants [164—167]. 

Non-ionic Polyoxyethylene alcohol Alkylphenol ethoxylate Polysorbate 80 w+x+y+z= 20, R=(C17H33)COO 

Propylene oxide-modified polymethylsiloxane E O = ethyleneoxy PO = propyleneoxy 

Lauramidopropyl betaine Cocoamido-2-hydroxy-propyl sulfobetaine 

Many methods have been developed for the quantitative determination of each class of surfactants. The analysis of commercial surfactants is much more complicated since they may be comprised of a range of compounds within a given structural class, may contain surface-active impurities, may be formulated to contain several different surfactant classes, and may be dissolved in mixed organic solvents or complex aqueous salt solutions. Each of these components has the potential to interfere with a given analytical method so surfactant assays are sometimes preceded by surfactant separation techniques. Both the separation and assay techniques can be highly specific to a given surfactant/solution system. Table 3.4 shows some typical kinds of analysis methods that are applied to the different surfactant classes. 

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