CMC for SDS?

john markwell markwell at unlinfo.unl.edu
Wed Feb 23 09:12:28 EST 1994


sspencer at rhino.bocklabs.wisc.edu (Stephan Spencer) writes:

>Could someone tell me what the CMC is for SDS? The buffer it is in is 150
>mM NaCl, 10 mM MgCl2. (pH 7.5, 25 C). What is a good reference text for
>this kind of information? 

>Thanks much!

>-- 
>Stephan Spencer
>University of Wisconsin, Biochemistry
>sspencer at rhino.bocklabs.wisc.edu


The cmc for SDS changes with ionic strength and temperature.  It is 
quite sensitive to the presence of divalent cations such as Mg++.  I 
would suggest that a good starting reference is M.J. Rosen (1978) 
Surfactants and Interfacial Phenomena, John Wiley & Sons, New York.  
This reference contains cmc listed at a variety of temperature and 
ionic strength.  It also gives a good, basic explanation of what is 
going on in solution.

We have found that if cmc in your solution really matters, then it may
be worthwhile to actually measure it under your conditions with a Du 
Nouy tensiometer [cf. Bartzatt et al (1983) Biochim. Biophys. Acta 
725: 341-348.  Because protein and membranes can bind up a significant
amount of the SDS (or MgDS), the bulk phase concentration is lower 
than you estimate.  Any physical chemistry teaching lab should be able
to loan you a tensiometer.

I hope this helps.

--
John Markwell			Phone: 402-472-2924
Dept. Biochemistry		FAX:   402-472-7842
University of Nebraska		Internet: markwell at unl.edu
Lincoln, NE  68583-0718



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