I'm having problems with precipitation forming in a Tris
Buffer with LaCl3. The precipitate forms slowly on the gas-liquid
interface and is apparent after a period of 12-24 hours. The
formation of the precipitate is pH dependent. Precipitation does
not occur at pH below approximately 6.7. The amount of precipitation
increases with increasing pH. Furthermore, the precipitation
seems to be dependent upon the presence of atmospheric gasses.
If argon is used to purge atmospheric gasses from the Tris Buffer
and the solution is capped to prohibit gas transfer, precipitation
does not occur. Lanthanum is a common tool to study the transport
of Ca2+. I have read several references that use LaCl3 in Tris
buffers at concentrations 1 to 2 orders of magnitude greater than
the concentrations I am currently using with no mention of
precipitation problems. Does anyone have experience using
LaCl3 in a Tris buffer? Can anyone explain the precipitation
and help me find a solution to this problem?
Buffer Components:
10mM TrisHCl
0.8mM MgCl2
1.0mM CaCl2
5.3mM KCl
140mM NaCl
0.1mM LaCl3
pH adjusted with NaOH to a final pH of 7.4
Thank you for any help.
Steve Kenny
email: jkenny at bae.uga.edu
--
-----------------------------------------------------------------------------
J. Steven Kenny
E-mail: jkenny at ice.bae.uga.edu
WWW: http://www.bae.uga.edu/dept/grads/jkenny