Analysis of mixtures without separation

Many mixtures of surfactants can be analysed only after prior separation into the main classes, or by methods that are intrinsically separative, notably the various chromatographic techniques. Even in those cases where chromatography is not the only possible approach, it is often the most convenient and cost-effective. 

Nevertheless, there are many other mixtures of surfactants that can be analysed by classical methods without prior separation. Mixtures of surfactants of one type, e.g. the anionic, cationic and nonionic fractions recovered from an ion-exchange column, can often be so treated, the most notable exception being mixtures of different kinds of sulphonated hydrocarbons, which require high-tech methods. Mixtures of nonionics and of cationics are, however, not often encountered in practice, but a fair proportion of mixtures of surfactants of different classes can be analysed without recourse to high technology, and this is of considerable practical use. 

Because all the techniques required have already been covered in earlier chapters, only outline approaches are given here. Because of the enormous range of possible surfactant structures and combinations of components, it is inevitable that the generalised guidelines given here will sometimes fail, or succeed for only part of the analysis. 

Quite arbitrarily, solvent extraction of weak acids or bases as a first step in the analysis is considered for the purposes of this chapter to be prior separation. Solvent extraction of hydrolysis products during the analysis is, by definition, not prior separation. 

In the majority of cases the results must first be calculated in mol/100 g or in meq/g, and subsequently converted to a weight percentage by multiplying by the appropriate molecular weight in the first case and by one-tenth of the molecular weight in the second. 

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