Kratky plot
A Kratky plot is obtained by plotting scattering intensity as Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \scriptstyle I(q) \times q^2} vs. Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \scriptstyle q} (instead of simply Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \scriptstyle I(q) } vs. Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \scriptstyle q} ). This representation divides-out the decay of the scattering, making certain other features more evident.
In particular, a Kratky analysis is often performed on polymer solutions. Here, the shape of the curve in the Kratky plot helps identify the conformation of the polymer chain:
- A rise to a plateau indicates an unfolded chain (random coil)
- A distinct peak is indicative of a compact or folded conformation for the chain (in biological studies, this may be a protein in a well-defined/folded state).
- Other conformations can also potentially be distinguished:
- Pseudo-linear rise for rod-like conformation
- High-q upturn from the plateau indicates worm-like chain
- In polymer gels, a peak may indicate the presence of inhomogeneities, such as clustering.
- etc.
Practical
The validity of a Kratky analysis is strongly dependent on data quality. Only with a very careful and representative background subtraction can the analysis be considered reliable.
