Application of Sedimentation Coefficient

3 Application of Sedimentation Coefficient Molecular Weight Determination See Eq. (10.21). 

Characterization of Molecular Species The sedimentation coefficient can be used to evaluate the purity of a material. A sharp boundary is usually (though not always) an indication of the homogeneity of the particles. A broad boundary (asymmetrical) or more than one boundary grouped together is a clear indication that there is a heterogeneity of particles. The number of fast-moving molecules (e.g., dimers) can be estimated. Caution must be exercised, however, since the most serious consequence of the dependence of the sedimentation coefficient on concentration is a possible distortion of the boundary. Thus, before we draw any conclusions, the degree of dependence of S upon c must be assessed from a series of experiments performed at various concentrations. 

In biochemistry different species of the same kind of molecules are often labeled in terms of sedimentation coefficients. As an example, Escherichia coli ribosome has been separated into four different species, 30S, 505, 705, and 1005 (see 18.6). The larger the number of 5, the larger the size of the molecule. 

---