The 'critical micelle concentration' (CMC) of a detergent varies with temperature, pH, ionic strength, detergent concentration, purity and presence of organic agents in the detergent. Using a large excess of detergent may pose problems during purification procedures or other downstream applications.
A simple hydrophobic dye solubilisation method for the determination of CMC has been described and involves the solubilisation of a dye in a detergent solution only in the presence of micelles. The amount of dye solubilised is directly proportional to the micelle concentration. The CMC is determined by plotting optical density of the solubilised dye against detergent concentration. The points of inflection on the plot of observed data vs. detergent concentration correspond to the CMC of a typical detergent.
This method is simple and comparable to CMC determined by expensive light scattering or surface tension methods. Furthermore, this method is applicable to all detergents, including steroid based detergents such as CHAPS and deoxycholate, as well as non steroid detergents like β-octylglucoside.