From: Michael Morris <michaelm@pharm.usyd.edu.au>
  To  : Gresham Weatherly <gresham@unc.edu>
  Date: Thu, 16 Mar 2000 15:40:36 +1100

Re: baseline shift?

Dear Gresham,

I might make a couple of guesses. Are you using a layering oil in the bottom
of the centrepiece? This can make proteins precipitate and crash to the
bottom rather than sediment in the normal way.

Are the cells leaking between channels? Crossleakage between the sample and
the solvent channels may be causing the effects you are seeing. The
phenolphthalein test is useful for checking this (see Dave Teller's article
in Methods in Enzymology, Vol. XXVIII, pp. 346-441).

Yours, Michael


At 14:15 15/03/2000 -0500, you wrote:
>I've collected some weird data from a sedimentation equilibrium run.  It
>looks like the baseline is moving for my absorbance scans causing the scans
>to have increasingly less absorbance.  
>
>I've attached a file that has the absorbance scans for all three cells
>which all have six chambers.  Each cell has the same sample in all three
>sample chambers.  And the only difference between the cells is that I've
>added 0.25 M sucrose to cell 2, and 0.5 M sucrose to cell 3.  And for every
>chamber except the middle chamber in cell 1 the absorbance systematically
>decreases with time.  And the furthest chamber in cell 3 has the weird
>downward dip in the first scans (black and red).
>
>Has anyone seen this before and know what is causing this behavior in the
>absorbance scans?
>
>
>Gresham Weatherly
>Attachment Converted: d:\eudora\attach\overlays.pdf
>
>
>Department of Chemistry
>University of North Carolina
>Chapel Hill, NC 27599-3290
>Tel: Lab (919)962-1297, Home (919)933-7837
>Fax: (919)966-3675
__________________________________________________________________

Michael Morris
Senior Lecturer
Pharmaceutical Chemistry	  Tel:	+ 61-2-9351-2359
Department of Pharmacy A15	  Fax:	+ 61-2-9351-4391
University of Sydney 2006	Email:	michaelm@pharm.usyd.edu.au 
Australia			
__________________________________________________________________