Micellar properties of the zwitterionic bile derivative CHAPS.

The critical micellar concentration (cmc) of the zwitterionic bile derivative CHAPS has been measured by fluorescence, light scattering and vapour pressure osmometry methods. The latter technique has been found most convenient and reliable. At 25 degrees C, in pure water, a cmc near 9 mM is found. Temperature decreases only slightly the cmc, from 9 to 7 mM upon heating from 25 to 50 degrees C. pH, in the range between 4 and 11, does not affect the cmc of CHAPS. Ionic strength appears to induce a marked decrease in cmc: measurements in 40 mM KCl give values about one-half those found for CHAPS in pure water.