Setting a molecular weight standard

One method for determining molecular weight from a scattering profile is comparison to a known scattering profile with known molecular weight. This part will teach you how to set that known standard in RAW.

Note: The calibration dataset used for the first parts of this tutorial doesn’t have the requisite data to use for this part. So we will use the data in the calibration_data/extra folder.

A video version of this tutorial is available:

The written version of the tutorial follows.

  1. Load the SAXS.cfg file in the calibration_data/extra folder.

  2. Plot all of the lysbuf2_52_001_000x.tiff files, where x is 0-9, on the main plot.

  3. Average the lysbuf2 files you just loaded.

  4. Repeat steps 2-3 for the lys2_52_001_000x.tiff files.

  5. Subtract the averaged buffer profile (lysbuf2) from the averaged sample profile (lys2).

  6. Select the subtracted profile by clicking on it. In the information panel, set the concentration to 4.14 (this is concentration in mg/ml).

    • Tip: You will have to scroll down to the bottom of the Information panel to find the Concentration.


  7. Perform a Guinier fit on the subtracted profile.

  8. Right click on the subtracted profile and select the “Other Operations->Use as MW Standard” option.

  9. Enter the molecular weight of the standard in kDa in the box that appears. For this lysozyme sample, the molecular weight is 14.3 kDa.


  10. Click “OK” to save the molecular weight standard.

  11. Save the settings for future use.