Difference between revisions of "Guinier plot"
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| − | Guinier analysis attempts to extract the size-scale for a structure by fitting the [[scattering]] to an equation of the form | + | A Guinier analysis attempts to extract the size-scale for a structure by fitting the [[scattering]] to an equation of the form: |
| − | :<math>I(q) = I_0 \exp \left( - \frac{R_g^2}{3} q^{2} \right) </math> | + | :<math>I(q) = I_0 \exp \left( - \frac{R_g^2}{3} q^{2} \right) </math>, |
or equivalently, | or equivalently, | ||
:<math>\ln(I(q)) = \ln(I_0) - (R_g^2/3)q^{2} </math> | :<math>\ln(I(q)) = \ln(I_0) - (R_g^2/3)q^{2} </math> | ||
| − | Thus | + | Thus a plot of ln(''I'') vs. ''[[q]]''<sup>2</sup> can be used to highly the scaling of the scattering. A straight-line in such a plot is indicative of Guinier scaling. Such an analysis is typically only done with the low-''q'' portion of the data. Linear (Guinier) scaling suggests that the system is essentially monodisperse; it can thus be used as a means of quality control before further data analysis (e.g. [[Form factor]]). |
| − | + | ==Rule of thumb== | |
| − | * For spherical particles, <math>\scriptstyle q_{\mathrm{max}} < 1.3 R_g </math> | + | The larger one's particles are, the smaller the minimum ''[[q]]'' must be. One also only expects the Guinier scaling to be maintained up to a certain maximum ''q'': |
| − | * For elongated particles, <math>\scriptstyle q_{\mathrm{max}} < 0.8 R_g </math> | + | * For spherical particles, <math>\scriptstyle q_{\mathrm{max}} < 1.3 / R_g </math> |
| + | * For elongated particles, <math>\scriptstyle q_{\mathrm{max}} < 0.8 / R_g </math> | ||
==See Also== | ==See Also== | ||
Latest revision as of 11:10, 13 August 2020
A Guinier analysis attempts to extract the size-scale for a structure by fitting the scattering to an equation of the form:
- ,
or equivalently,
Thus a plot of ln(I) vs. q2 can be used to highly the scaling of the scattering. A straight-line in such a plot is indicative of Guinier scaling. Such an analysis is typically only done with the low-q portion of the data. Linear (Guinier) scaling suggests that the system is essentially monodisperse; it can thus be used as a means of quality control before further data analysis (e.g. Form factor).
Rule of thumb
The larger one's particles are, the smaller the minimum q must be. One also only expects the Guinier scaling to be maintained up to a certain maximum q:
- For spherical particles,
- For elongated particles,
See Also
- P. Thiyagarajan, T. S. Burkoth, V. Urban, S. Seifert, T. L. S. Benzinger, D. M. Morgan, D. Gordon, S. C. Meredith and D. G. Lynn pH dependent self assembly of beta-amyloid(10-35) and beta-amyloid(10-35)-PEG3000 J. Appl. Cryst. 2000, 33, 535-539. doi: 10.1107/S0021889899014387
- A. V. Smirnov, I. N. Deryabin and B. A. Fedorov Small-angle scattering: the Guinier technique underestimates the size of hard globular particles due to the structure-factor effect J. Appl. Cryst. 2015, 48. doi: 10.1107/S160057671501078X
- C. D. Putnam Guinier peak analysis for visual and automated inspection of small-angle X-ray scattering data J. Appl. Cryst. 2016, 49. doi: 10.1107/S1600576716010906
