The second momdent analysis will calculate weight-average sedimentation coefficients for each scan included in the analysis by finding the second moment point in the boundary. The second moment analysis can serve as a valuable diagnostics tool in identifying problems such as time-dependent degradation, aggregation and even concentration dependency. It is important to keep in mind that the second moment analysis is only valid for scans that have cleared the meniscus and still have a stable plateau. All other scans should be excluded from the analysis.
You start the Second Moment data analysis by clicking on "Second Moment" in the Velocity sub-menu of the main menu. The main Second Moment data analysis window will appear.
The first step in the analysis requires that you load an UltraScan dataset that has previously been edited with the UltraScan editing module. UltraScan sedimentation velocity datasets always have the suffix ".us.v". Click on the "Load Dataset" button in the left upper corner of the control panel. Simply select the desired run from the selection of available runs in the dataset loading dialog. Once loaded, the Run Details will be shown. Click on the "Accept" or "Cancel" button, and you will be returned to the analysis window, which will show the first available dataset of the selected run in the edited data window on the lower right panel, and the Second Moment analysis will be shown in the upper right panel of the analysis window.
|Click on these buttons to control the Second Moment analysis:
|Here you can enter the corrections for density, viscosity, and partial
specific volume of your sample. As you change the information in these
fields, the program will automatically update the analysis to correct the
S-value according to the specified buffer conditions. If the data was
retrieved from the database and associated with the correct buffer file
and peptide file, the density, viscosity and partial specific volume (vbar)
will automatically be updated to the appropriate values and don't need to be
adjusted to produce S 20,W corrected values.
Utility of Second Moment Analysis:
The Second Moment Analysis provides useful diagnostics to determine certain properties of a velocity experiment. It will not, however, provide information about the distribution of S-values present in the sample. The van Holde - Weischet methods is better suited for this purpose. The strength of this method is its ability to detect the following features:
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Last modified on January 12, 2003.