Identification and determination of ionic surface active agents.

A general colorimetric method has been developed to analyze either anionic or cationic surfactants in fresh water. An appropriate dye will react with ionic surfactant to form a chloroform-soluble, colored complex in the presence of chloroform. The color intensity of the vigorously rocked and subsequently settled chloroform layer is proportional to the concentration of the "dye-ionic surfactant complex", and can then be measured by making spectrophotometric readings of the chloroform solution at the optimum wavelength of the instrument used. When cationic surfactants are to be analyzed, methyl orange shall be used as a dye; when anionic surfactants are to be analyzed, azure A or methylene blue shall be used as a dye; Other chemical reagents, apparatus and spectrophotometers, however, can be nearly identical for either cationic surfactant or anionic surfactant measurement. The new analytical method is stoichiometric, and can be easily performed by a laboratory technician within a very short period of time.