van Holde - Weischet Tutorial
Careful experimental design is an important factor determining the amount
and resolution of the information obtained from an experiment.
The following considerations influence the quality of the results:
- Range of scans: Always collect data for sedimentation spanning the
entire cell. It is easy to discard unusable data later on, but impossible
to generate missing data later on. Always start collecting immediately as
soon as rotor speed is reached. Scans that didn't clear the meniscus can
be discarded for the van Holde - Weischet analysis, but may be useful for
fitting in the finite element analysis.
- Number of scans: Get as many scans as possible. The more scans are
available, the higher the confidence in the linear extrapolation, and
the more easily problems are identified. Always minimize the time between
scans to maximize the number of scans collected for each cell.
- Rotor speed: run as fast as possible since the faster the speed, the
higher the resolution of the data (this is a tradeoff with the number
of scans the machine can physically measure in the shorter time period
resulting from the higher speed).
- Keep in mind that later scans generally show an improved resolution
of multi-component systems. Analyze the system with different cropping of
scans (the later scans) to see if resolution improves.
- For unknown samples, always measure 3 different concentrations
spanning at least a 10-fold concentration range, better more. This can
often be accomplished by changing the wavelength, or by changing to
interference optics, if available.
- It is important that the temperature stays constant throuhout the run.
Precooling the rotor and equilibrating the rotor at run temperature
for at least 30-45 minuted before the run starts is recommended.
www contact: Borries Demeler
This document is part of the UltraScan Software
Copyright 1998, 1999, The University of
Texas Health Science Center at San Antonio.
The latest version of this document can always be found at:
Last modified on June 12, 1999.