[RASMB] sedimentation

[John Coropisnita]

Dear Colleagues,

I would like to ask you the following questions
(I am performing sedimentation velocity measurements
on small silica particles).

1. Since the Beckman's software does not give 
reproducible results of sedimentation coefficient
when using the second moment method, I would
appreciate
any suggestion about a good software for determining
this coefficient as well as the diffusion coefficient.

2. In some cells I noticed that the reference (pure
grade ethanol, taken from the same vial) has an
absorbance of -0.2 to -0.5 OD, while in other cells it
is zero. I noticed this when I measured very diluted
dispersions (and not when more concentrated were
measured); The meniscus of the reference
in the above case has also a strange shape. The
phenomena was reproducible after the cell was
refilled.
The window glass was carefully cleaned.

Have you seen something similar?

Thank you very much,

Jan.

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