[RASMB] Bad scans from XLA

[James]

Dear RASMB members,

 

I have recently been struggling with a recurring problem when I centrifuge
10 and 20nm gold particles that causes my XLA to generate poorly formed OD
data scans that cannot be fit by Sedfit. I had initially been getting well
formed scans that were easily fit by Sedfit using the continuous c(s) model
however after half of the sample side in one cell (in a 4 cell rotor) leaked
out during a run I was no longer able to get the nice sigmoidal scans that I
originally had even though I tightened and refilled the leaking cell. I
asked the Beckman service rep to investigate and he cleaned the optics and
told me to have the XLA perform a radial calibration and the scans were back
to a sigmoidal shape using the same sample of gold nanoparticles and Sedfit
could fit the data well again. However after another cell leaked in the
centrifuge, the scans could not be fit with Sedfit even though the cell was
tightened and refilled and no longer leaked. I have been performing a radial
calibration before each run and have not turned off the delay calibration
hoping the instrument will recalibrate and improve the scans however, this
has not happened. I have attached screen shots showing the quality of the
data before and after the cell leak. It looks like it could be the optics
but I am not convinced this is the whole story since it seems extreme that
one cell leak can alter the XLA performance this much until the optics are
cleaned.

 

 

James B. Falabella

Process Sensing Group

National Institute of Standards and Technology Gaithersburg, MD

Tel: 301-975-5041

Fax: 301-975-2643

 

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