making electrophoresis boxes

HARDIES at THORIN.UTHSCSA.EDU HARDIES at THORIN.UTHSCSA.EDU
Sat Dec 3 11:12:05 EST 1994


Daniel Kim writes:

>  ...[when making gel boxes] I am aware that most of the wires used for 
> electrophresis electrodes are made of platinum.  Is there a reason for this?
> Why can't stainless steel be used?

The electric field hydrolyzes the water causing hydrogen ion to migrate to
the negative electrode and bubble off as hydrogen gas.  OH- migrates to the
positive electrode where it gives up its electron.  You want it to end up 
as H2O + oxygen gas, but if the extra oxygen can easily oxidize the metal
instead, it will.  So you need a positive electrode that is highly resistant
to oxidation or else it will corrode in no time.  Platinum is the usual 
choice; stainless steel or copper are a disaster; I don't know if there
are other metals that work.

Note that all of the metal in contact with the solution has to be
corrosion resistant. If you design the box so that people can overfill
the chamber and get buffer in contact with the terminal to which your
platinum connects, then that terminal will corrode almost immediately. 
So it pays to make the box so that you can't get the buffer in contact
with any metal but the platinum.  Whatever you do, make it so that the
terminal is easily replaced.

Platinum can easily become the major cost of the gel box.  It's common
to use a very narrow guage of platinum wire to cut the costs.  Then
the electrode becomes prone to mechanical breakage.  So when you
figure out how to attach it to the box: 1) try to secure it so that
people can't wiggle it around and break it, and 2) make sure that it
will be easy to take in and out, because you will end up replacing it
if the box is heavily used.  Ideally, you'd like to be able to
take the broken pieces out, intertwine them, and just put them back.

Hope this helps.

Steve Hardies, Dept. of Biochem., Univ. of Texas HSC at San Antonio
Hardies at thorin.uthscsa.edu




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