Amphoteric surfactants can function either as anionic or cationic surfactants, dependingon the pH of the system. They contain both anionic and cationic functions in the samemolecule. More costly to produce than ionic surfactants, amphoteric surfactants representonly about 3% of surfactant volume in Europe and less than 1% in the United States. Theyare less irritating than other materials and are largely used in personal care products. Adistinction can be made between amphoteric and zwitterionic surfactants. This distinctiondoes not affect their analysis. For the analyst, a more important distinction is between amphoterics with a secondary or tertiary amine group and those containing a quaternaryamine function. The former only have cationic properties when protonated at low pH,while the quaternary amines have cationic properties even under alkaline conditions.A very thorough discussion of these compounds comprises a volume of the Surfactant Science Series (1). We adopt the organization and terminology of Lomax (1) and thenames used by the CTFA (2).
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