Effect Guinier plot

Step 3 Guinier Plot Separation of Size and Distortion Effects. The inner part of the correlation functions y0bs(h) (T) s readily expanded into a power series. For this purpose we resort to Eq. (8.14). Assuming that instrumental broadening is already eliminated we have... 

In most of the physical studies made to date there is little evidence of sufficient care being taken to assure sample quality. Especially pronounced is the effect this has on scattering results curvature of the Guinier plots (which provide the radius of gyration) due to polydispersity allows only an approximation of the radius of gyration at best. 

A Guinier plot of deuterated calmodulin-peptide complex (Heidorn et al,1989) showed a sharp change of behaviour at the match point for the peptide. The Guinier plot was effectively due to the calmodulin part of the complex, with little contribution from the peptide. 

Sample concentrations in the range 1-10 mg/ml are usually sufficiently dilute that no correlations due to interparticle interference effects will occur. These would be evident from reduced I Q) values at low Q in Guinier plots or a negative trough near in D(r) plots. Qualitatively, the distance between particles, which is given by M,/c should be larger than In/Q. When Q > - 5 (depending on... 

The salt effect on the structure of the solution was also studied [60, 69]. The scattering spectra are dramatically affected - the interference peak disappears and the intensity scattered at low Q increases - when a simple salt is added to a concentrated solution. At low polymer concentration, the Guinier plot remains unchanged except for an increase of the scattered intensity at very low Q values (Fig. 19.10). These effects were attributed to a decrease of the order associated to the beginning of aggregation without any change in the shape and the size of the particles. The quantity of salt necessary to affect the interference peak in concentrated solutions is related to the dielectric constant of the solvent. The same effect occurs respectively with 10 , 10" and 10 mol/1 of added salt in ethanol, water and N-methylformamide solutions [69]. 

Figure 5.—Continued. Typical Guinier and Debye plots observed for PBLG-138,000/toulene prepared by quenching to various temperatures d) T = 28.3, NOT RENEWED. Comparing a) and d) shows the effect of not renewing the sample by a long, high temperature melt between runs the intensity of the unrenewed sample is much less, resulting in some imprecision at the lowest angles. Fully darkened points were not used in obtaining slopes.

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