Web Analysis Guinier plot


This webtool uses Highcharts 3.10 under a non-comercial licence and the regression.js library under an MIT licence.

Guinier law

This web-tool performs a Guinier analysis of the uploaded small angle scattering data (SAS) data. Determined by Andre Guinier in the 1930's, Guinier's law describes how the radius of gyration (Rg) and forward scattering intensity (I(0)) of a normalised background-subtracted small angle scattering plot can be estimated from the following equation: -

The terms of this equation can be determined by plotting the data as Ln I(q) versus q^2. From the slope of the curve and its intercept at 0 on the x-axis, the radius of gyration (Rg) and forward scattering intensity (I(0)) can be determined as shown in Figure 1.

Figure 1) A Guinier plot and how each term is derived in the valid region


The web application loads 3 column (Q, I(ntensity), E(rror)) Comma separated value (Csv) files or text file, with either comma or space separation, and also ATSAS *.dat files with one line headers, i.e :-

Q,I,E

0.009,2.70E-01,5.27E-02

0.011,2.53E-01,3.63E-02

0.013,2.32E-01,2.38E-02

0.015,2.25E-01,1.69E-02

Example model data files generated using Crysol from the Lysozyme structure (Pdb: 1HEL) are given here: 1HEL.txt , 1HEL.txt , 1HEL.dat . It has a theoretical Rg of 15.38 A.

B) Data display

1) The data in the format given above can be located and graphed in the data viewer as shown in Figure 1.

 

Figure 2) The data can be loaded and displayed in either Log (I) - q (Semi-log) or Log(I)-Log(q) scale

2) The data can either be viewed in Log(I)- q profile, which is useful to examine the data at high-q, or Log(I)-Log(q), which is useful to examine the samples polydispersity.

3) The graph can be printed directly or downloaded in a number of formats (*.png, *.jpeg, *.pdf, *.svg).

C) Guinier Analysis

The loaded data is displayed as a Guinier plot (i.e. ln(I) versus q^2).

1) Specify a region by changing the data points in the plot and perform a Guinier analysis. As shown in Figure 3, a valid Guinier analysis will give an estimate of the radius of gyration (Rg) for the particles in the sample and the forward (zero angle scattering intensity (I(0)). A Guinier analysis is only valid in the low-q region of a SAS plot, the maximum point of this region for small globular proteins is said to be when q.Rg = 1.3.

Figure 3) A Guinier plot of the data given in Figure 1

2) You can zoom into and out of the Guinier plot.

 

Figure 4) A close up of the Guinier plot

3) The displayed graph can be printed or downloaded.