Ptitsyn-Eisner equation

The Mark-Houwink plot for the pullulans is displayed in Figure 9 and indicates a smooth relationship with little scatter. A slope of 0.64 was obtained from the best fit. Figure 10 displays a double logarithmic plot of the radius of gyration versus the molecular weight for pullulans, and this plot has a slope of 0.37. The theoretical values of Rg were calculated by using the Ptitsyn-Eisner equation (as follows) and are shown in the same figure 11) ... 

Figure 10. Double logarithmic plot of radius of gyration versus molecular weight for pullulans. Theoretical slope obtained from Ptitsyn-Eisner equation (see text).

It appears that for low values of Rg (10-20 nm), the values of Rg that were calculated from the Ptitsyn-Eisner equation were more reliable than those obtained from light scattering in an aqueous medium. Accordingly, for accurate work over a broad range of molecular weights and sizes, a triple detection system is advantageous and recommended. 

This equation indicates that 0 is not strictly constant but decreases with increasing molecular weight and solvent power. A similar conclusion has also been advanced by Ptitsyn and Eisner (277, 218) for essentially the same reason, although their calculation differs in detail. 

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