Comment on "Determination of the critical micelle concentration of dodecylguanidine monoacetate (dodine)".

In a work published in this journal by J.P.S. Cabral and A.R.W. Smith [J. Colloid Interface Sci. 149 (1992) 27], it is reported that the 1-dodecylguanidinium acetate (dodine) exhibits first CMC at 20-30 microM and second CMC at 110-120 microM in aqueous solution at 22.5 degrees C. Such low CMCs are unusual for ionic surfactants with dodecyl chain, and is quite interesting if this is the case. Thus, we investigated the micelle formation of dodine by electrical conductivity measurements. The specific conductivity, kappa, vs concentration plot showed no evidence for micelle formation up to a few hundreds microM at 25 degrees C. The Krafft temperature of dodine was found to be approx. 52 degrees C. When conductivity measurements were made at 54 degrees C, a clear break point was observed in the kappa vs concentration plot at 9.5 mM, which must correspond to the CMC of dodine. This CMC value is quite normal for cationic surfactant with dodecyl chain.