Field of Science

Why does white gunk develop on the anode?


The gunk is soft, almost-gel-like.  In the photo it's sitting in lumps in the buffer in the bottom tank, but only because I gently scraped it off the anode wire with a spatula after I took the gel plates out of the apparatus.  The anode was clean before I ran the gel.

The gel buffer was TBE with 10 mM MgCl2 added; might this be Mg(OH)2?

Later:  The white gunk is alkaline and dissolves in acid but not alkali.  It's not from the gel.  It also appeared when I ran a test minigel using TAE buffer with 10 mM MgCl2 added.


  1. No SDS; this is a simple DNA gel.

  2. What is the anode material? It could also be a variety of chloride species, as the positive electrode can get oxidized, and then combine with Cl-. Thus, depending on anode material, I would guess you either have Mg(OH)2 or M(Cl)x, where M is the anode metal, and would only be likely if it is silver...

  3. Are you sure it's not just pieces of the gel itself?

  4. I've seen this before. It's definitely related to the Mg. I used to run lots of gels in TBM (Tris, borate, MgCl2) and they'd always have that build-up on the anode wire. But only when Mg was included; never otherwise.

    Don't worry about it. We ran literally hundreds of such gels in mini-gel rigs and never had any problem with the stuff. Didn't see any sign that it ate up the anode, e.g.


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