[RASMB] fringe deviation

[Tom Laue]

Hi folks,
One more comment regarding gradients and shlieren effects in the XLA. 
Steep gradients do not have to produce the "dreaded black bands" (I like 
that description!) to cause inaccuracies in the absorbance readings. 
Helmut Colfen and Steve Harding studied this phenomena using an older 
design of the XLA optics:
H. Colfen and S. E. Harding. A Study on Schlieron patterns derived with 
the Beckman Optima XL-A UV-absorption optics. Progr.Colloid Polym.Sci. 
99:167-186, 1995.
Two things to note: 1) the newer XLA optics (on everyone's machine) are 
far less susceptible to the schlieren effects described in this paper 
and 2) one can test for a problem very quickly and easily by scanning at 
a non-absorbing wavelength (e.g. 320 nm for protein) and observing 
whether there are bumps in the trace at positions where there is a boundary.
Best wishes to all,
Tom

-- 
Department of Biochemistry and Molecular Biology
University of New Hampshire
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