SOMO SAXS/SANS (SAS) UV-Vis Module Options

| # Manual

## SOMO - SAXS/SANS (SAS) UV-Vis Module Options

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Last updated: June 2024

In this module you can first set a basic parameter of the detector used by pressing the Concentration Detector Properties button, opening another window:

Check the checkbox and enter a factor that will convert your detector's units into Absorbance units [AU]. In the example shown, the used detector output is already in AU, so "1" is entered. If your detector output is, for example, in milliAU, you should enter "0.001" here. Pressing Quit will exit without retaining any input, pressing Keep will exit keeping any input entered but not saving it in a file, pressing Save will exit keeping any input entered and saving it in a specific US-SOMO configuration file (default: somo_uv_vis_default_dctr.dat).

Pressing the UV-Vis Processing Parameters button will open another window:

This section will let you save several parameters that are specific of the experimental sample and buffer used. These parameters can be saved in a specific file for each sample/buffer, from which they can be recalled.

- The first field will let you enter a Title that will remind you of the sample/buffer used upon reloading.

- Lambda is where you can enter a specific wavelength [nm]

- Extinction coefficient [mL mg-1 cm-1] is for its associated extinction coefficient. These two entries will enable obtaining directly a concentration [mg/mL] after processing your UV-Vis data.

The second section deals with the wavelength-dependencies of the square roots of the refractive index [n(λ)]0.5 and of the differential increment of the solute refractive index as a function of the concentration in that buffer [[dn/dc](λ)]0.5. These parameters will be used by the UV-Vis module to correct absorption spectra for scattering effects in turbid of very large solutes samples. These two dependencies must be evaluated by the user first determining the n(λ) and [dn/dc](λ) values at several wavelengths for the buffer/sample couple at the experimental temperature, using for instance the freely-available program SEDNTERP3 (downloadable here). The square roots of these values are then fitted with power laws:

[n(λ)]0.5 = A+B*λC

[[dn/dc](λ)]0.5 = A+B*λC

and the A, B, and C coefficients are then entered in the respective fields in this section.

See above for the usage of the Quit, Keep, and Save buttons. The default configuration file in this case is somo_uv_vis_default_uv_vis_param.dat. Load will allow to retrieve a specific file with all the parameters of a previously saved particular sample/buffer combination.

Back to the initial screen of this module, the Save CSV transposed checkbox if selected will save any resulting csv-style files with the columns-lines transposed in respect to what is normally produced. This migh be useful if, e.g., one wants the absorbance as a function of the wavelength or vice-versa. Default: unselected.

www contact: Emre Brookes

This document is part of the UltraScan Software Documentation distribution.
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Last modified on June 24, 2024