Dear All,

Has anyone successfully used an Iodixanol gradient in a Beckman XLA??
Or, any other non-ionic density gradient media?

I am having problems with it.  It seems like the problem is due to a
phase separation or de-mixing of the iodixanol and water (not due to the
sedimentation of the Iodixanol molecules). 

I used the following ingredients:

250 mL of 60% (w/v) Iodixanol (Optiprep)
20 mL of 1 M TRIS Buffer (pH 9)
230 mL of DI H2O

XLA was run at 27000 rpm at temperature 25 C
I took the velocity read at wavelength = 514 nm

I was expecting to see a clear absorbance profile but it turned out that
there were large peaks on the top (nearest to the spinning axis) and the
bottom (farthest from the axis) – not to be confused with the meniscuses. 
I believe these peaks in absorbance are not due to absorbance at all but
due to the optically un-uniform solution.  I took the cell out of the
centrifuge and it seemed that phase separation or de-mixing had occurred. 
The gradient did not appear optically uniform, even in the angular direction.

Has anyone had this problem or is there anyway around this problem?

Regards to all,
Jin Suntivich