Water soluble trivalent cation

[WANDERS at INDYVAX.IUPUI.EDU]

I would like to make Percoll buoyant density gradients containing a
trivalent cation.  I have made Percoll gradients with NaCl and MgCl2.  
However, both AlCl3 and FeCl cause Percoll to turn cloudy and gel due to 
the low pH of Al3+ and Fe3+ solutions. pH 4 t0 7 solutions are insoluble.  
I need a trivalent,cationic, water soluble substance that doesn't react 
with Percoll solutions.
Reply to wanders at indyvax.iupui.edu
W. Marshall Anderson
I.U. Sch. Med.
NWCME
3400 Broadway
Gary, IN 46408 USA