Abstract
The microdetermination of anionic surface-active agents was carried out based on the fact that anionic surfactants generally inhibit the enzyme reaction, and moreover trace amounts of cationic, nonionic and amphoteric surfactants were determined by using the phenomena that these surfactants apparently suppress the inhibition of enzyme activity by anionic surfactants.
Substrate, 1-naphthyl acetate, was allowed to react with enzyme cholinesterase and the change in absorbance due to formation of 1-naphthol was automatically recorded at 324nm. Surfactants inhibit the enzymatic hydrolysis and cause decreases in the slopes of the absorbance-time curves. Using the degree of the inhibition abilities, the surfactant concentrations were determined. Using this method 20 to 200ppm of sodium linear dodecylbenzenesulfonate could be determined. When enzyme was previously incubated with sodium linear dodecylbenzenesulfonate and then the substrate solution was added to the mixed solution, 10 to 45ppm of the surfactant could be determined.
When 50ppm of sodium linear pentadecylbenzenesulfonate was previously added to substrate solution as an inhibitor, cationic, nonionic, and amphoteric surfactants diminish the inhibition and the absorbance increases. By this method the determination of 2 to 20ppm of dodecyl trimethyl ammonium chloride, 6 to 100ppm of polyoxyethylene dodecyl ether, 10 to 300ppm of polyoxyethylene octyl phenyl ether and 30 to 100ppm of dodecyl betaine has become feasible.
