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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:
.. raw:: html
<style>.embed-container { position: relative; padding-bottom: 56.25%; height: 0; overflow: hidden; max-width: 100%; } .embed-container iframe, .embed-container object, .embed-container embed { position: absolute; top: 0; left: 0; width: 100%; height: 100%; }</style><div class='embed-container'><iframe src='https://www.youtube.com/embed/tj1dunGbLYo' frameborder='0' allowfullscreen></iframe></div>
The written version of the tutorial follows.
#. Load the **SAXS.cfg** file in the **calibration_data/extra** folder.
#. Plot all of the **lysbuf2_52_001_000x.tiff** files, where x is 0-9, on the main plot.
* *Tip:* :ref:`Section 1 Part 1 <s1p1>` of this tutorial document teaches you how to do this.
#. Average the **lysbuf2** files you just loaded.
#. Repeat steps 2-3 for the **lys2_52_001_000x.tiff** files.
#. Subtract the averaged buffer profile (**lysbuf2**\ ) from the averaged sample profile
(**lys2**\ ).
* *Tip:* :ref:`Section 1 Part 1 <s1p1>` of this tutorial document teaches you how to do this.
#. 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.
|config_mwstd1_png|
#. Perform a Guinier fit on the subtracted profile.
* *Tip:* :ref:`Section 1 Part 2 <s1p2>` of this tutorial document teaches you how to do this.
#. Right click on the subtracted profile and select the “Other Operations->Use as MW Standard” option.
#. 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.
|config_mwstd2_png|
#. Click “OK” to save the molecular weight standard.
#. Save the settings for future use.
.. |config_mwstd1_png| image:: images/config_mwstd1.png
:target: ../_images/config_mwstd1.png
.. |config_mwstd2_png| image:: images/config_mwstd2.png
:width: 450 px
:target: ../_images/config_mwstd2.png
|
