Surface-active properties and molecular aggregate formation of glycyrrhizic acid (GA) were examined by the measurement of surface tension, light scattering, light absorption of Rhodamine 6G (R-6G) solution or iodine solution, and fluorescence of R-6G solution. It was found that each physico-chemical property plotted against GA concentration showed a transition at a certain concentration, which indicated the formation of molecular aggegrates. The critical micelle concentration (CMC) values determined by these different methods were in good agreement. The spectral change method using the aqueous dye solution or the aqueous iodine solution seemed to be convenient because of the ease of its experiment. However, the definition of CMC by this method is somewhat arbitrary and the CMC value is sometimes influenced by the concentration of dye or iodine added. It is therefore essential to choose a suitable procedure for determining the exact CMC value from the plots of absorbance vs. concentration and to correct the CMC value for the effect of additives.
