As cationic surfactants are readily precipitated into reineckates, identification of 27 cationic surfactants of various types and different chain lengths were attempted with the methods of infrared spectroscopy and paper chromatography.
Surfactant reineckates were prepared as follows ; 1% aqueous ammonium reineckate solution was added into 2% aqueous (or ethanol) solution of surfactants.
Infrared spectra were obtained by potassium bromide disc technique, and the solvent system in paper chromatography was methanol : water : 35% hydrochloric acid (12 : 12 : 1).
Surfactants used for the present experiment were separated into the following three groups ; group A : amines and quaternary ammonium salts, group B : surfactants of pyridine ring, and group C : amphoteric surfactants, which have characteristic infrared absorption bands.
Each group could be differentiated and surfactants in three groups could be identified by infrared technique.
Both the absorption bands of surfactants (7001, 800 cm-1) and those of reinecke ion (3, 0003, 500 cm-1) in infrared spectra of surfactant reineckates could be used in the identification of surfactants.
Alkyl chain lengths could be differentiated with paper chromatography, but in this case, surfactant reineckates were treated with silver nitrate. Rf values of C12, C14, C16 and C18 except for primary amines were 0.680.78, 0.390.50, 0.170.21and 0.000.06 respectively.