Detection, sensitivity and data processing

Analyses are often required on surfactant mixtures or on complex matrices containing surfactants. In the latter case extraction procedures may have to be carried out, and for trace analysis, concentration steps will also have to be introduced. In more favourable cases, analysis of surfactant mixtures can be carried out without prior separation. FAB can be applied directly to mixtures of surfactants of all classes. 

TLC may be used to separate mixtures of anionics, cationics and nonionics, prior to FAB analysis, which is carried out on silica removed from appropriate regions of the plate. Mixtures of nonionic surfactants may be separated and analysed on-line by SFC-MS or LC-MS, or GC-MS for the low-EO species. 

Analysis of El spectra may be aided by reference to spectral libraries. However, many ionisation techniques used in the analysis of surfactants do not provide library-searchable spectra, either because the technique is too irreproducible or because the spectra contain too little structure. In any case, libraries should never be used as the only means of spectral interpretation experience, common sense and knowledge of the chemistry of the sample must also be used. The interpretation of mass spectra is rarely unequivocal, and whenever possible other methods of analysis should be used in conjunction with MS. 

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