[RASMB] two technical questions

Borries Demeler demeler at biochem.uthscsa.edu
Tue Jul 27 06:23:32 PDT 2010


> Hi RASMB,
> 
> 1) I'm working with an XLI spinning an 8hole rotor fully loaded with 8 =
> cells running the instrument at 40krpm.  It takes the instrument 20 =
> scans to reach top speed.  This was determined by taking omega from =
> omega-squared t, which I took from the second line of the header of each =
> absorbance scan file.  I'm not sure if this is the normal behavior of =
> this instrument and it seems to me a fairly long period of time to wait =
> for the instrument to come to speed. As I see a number of posts which =
> note that software such as UltraScan correct data collected during the =
> early part of a scan for acceleration effects, perhaps this is entirely =
> normal behavior and not worth worrying about?

Hi John,

Virgil is correct on both items, I just would like to add that you should
make sure that acceleration rate is set to 400 rpm/sec, the max the machine
can do. In that case it should only take about 1.7 minutes to get to 40 krpm.
You need to look at the rotor speed entry in the file header, not the w^2t
field, to find out what the actual speed is. Moreover, as far as I know it is
not possible to scan *until* the rotor has reached the selected speed, so I
am not sure why you say you can see 20 scan before speed has been reached.

> 2) If one performs a wavelength scan with the instrument in absorbance =
> mode, using a step size of 1nm increments, should one expect to observe =
> in the data file absorbance data at 1nm increments?  If one observes =
> wavelength steps that vary +/- 4nm, could this be a problem?

That's actually normal. I would run at least 3 repetitions of the wavelength
scan, this will increase your chances of hitting each wavelength. Running in
continuous mode will speed up the scanning a bit.

-Borries



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