Analysis of cationic and amphoteric surfactants II: Determination of their homolog distributions by reaction gas chromatography on the basis of the Hofmann degradation

Abstract and Summary

Pyrolysis and reaction gas chromatography (GC) methods have been investigated for the homolog distribution analysis of cationic and amphoteric surfactants containing a quaternary ammonium group. Pyrolysis GC was found to be inapplicable to the analysis of amphoteric surfactants because of the formation of the nonvolatile compounds as the main products. However, when cationic and amphoteric surfactants dissolved in a 3% potassium hydroxide methanolic solution were injected into a gas chromatograph, Hofmann degradation occurred at the injection port of a gas chromatograph (reaction GC), and we obtained about the same products as were formed by the older DMF-Methylate method. Under optimum conditions, various cationic and amphoteric surfactants were degraded almost quantitatively, and the reproducibility of this method was satisfactory. Furthermore, the homolog distribution of surfactants found by the reaction GC method closely agreed with that of the starting alkyldimethylamines used. Thus, reaction GC analysis was applicable to the homolog distribution analysis of these surfactants. The reaction GC method surpassed the DMF-Methylate method with regard to the simplicity and reproducibility of the determination.