Guinier analysis in Python (or similar):
  • Import and plot the data. Use a log scale for the y-axis. You can use any program for this, but if you use Python, you can use this python plotting script.
  • Generate a Guinier plot, by plotting $\ln(I)$ vs $q^2$ ($\ln$ is the natural logarithm). You may use this script.
  • Determine the Guinier region, where the linear relation is true (e.g. by zooming in on the plot).
  • Determine the maximum value of $q$ at which the data is still linear in the Guinier plot (remember the x-axis is $q^2$).
  • Forward scatteing ($I(0)$) and radius of gyration ($R_g$) are determined from the slope ($a$) and interception ($b$): $I(0) = \exp(b)$ and $R_g=\sqrt{-3a}$.
  • Make a Guinier analysis by (1) fitting a straight line to the curve, (2) determine the slope, (3) determine the interception with the y-axis to estimate $I(0)$ and $R_g$. You may use this Python script (you need to set the $q_\mathrm{max}$ in the script).
  • Lysozyme is globular. Check your value of $qR_g$ (max 1.3) and adjust $q_\mathrm{max}$ accordingly.
  • Congratulations, you have done a Guinier analysis!