Electrophoresis electrodes.

I have been trying to determine which materials work for electrophoresis electrodes.  My hope was that I could find something cheaper than platinum (I know it will work but it cost a lot).  Below are some things I have tried and the results.

  • Copper – Dissolves in solution and makes the solution blue-green (based on reports from various websites, only listed material I did not test).
  • Generic wire (22 gauge) – Mix of copper and iron.  Works as an anode but not a cathode.  As an anode copper leaked into solution and the wire became green and red striped, presumably because the braided strands were different materials.
  • Sterling silver (24 gauge) – Mix of silver (~90%), copper (~5%), and other elements.  Does not work for anode and I have not tested it as a cathode.  As an anode it leaked copper into solution, a black precipitate formed (steel was the cathode in this test) on top of both electrodes and the majority of the wire disintegrated.
  • Braided steel cable (around 1mm in diamter) – Intended as a “steel leader” for fishing.  Works as an anode but not as a cathode.  If it is used as a cathode it will disintegrate and break.
The failures I had have finally convinced me to purchased platinum wire.  The platinum will work for sure but I do not know if what I bought was thick enough so I will have to wait until it arrives in the mail.
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9 Responses to “Electrophoresis electrodes.”

  1. Flo Says:

    What about graphite ?

  2. Emma Says:

    I have tried most of this wires as cathodes and they decomposed.once I lay my hands on platinum I will give it a trial. I will also try alminium to see what happens. Thanks

    • CodonAUG21 Says:

      Likely aluminum will fail too. I think platinum is the only practical solution. I have had to rebuild my gel boxes twice because I mistakenly reversed the electrodes when plugging them in which caused the steel and silver to break down.

  3. CaptainCheap Says:

    One thing that you could look at would be gold – it is nit QUITE as expensive as platinum, and it’s almost as non-reactive, I think.

    I think there may be a way to use graphite that doesn’t require odd shapes. Instead of one long graphite rod across the box, you might be able to have many shorter strait pieces, each dipping into the solution along the end of the box (down to the bottom, of course). This has the benefit of that the average current from a given point will be more… well, averaged. So more constant.

    You might think it hard to connect so many graphite bits up, but there’s actually an easy way to do it, which makes use of a cheap conductive polymer I’ve been using for years: silicone mixed with key grindings. The concentration of key grindings needs to be pretty high, but there is a point at which it is very unlikely for any point, any small grinding, to not be connected to the bulk. For more on this, see Percolation Theory, or just take my word on it ^.^

    The silicone acts as a rubbery matrix into which anything can be stuck if it can pierce the silicone (so wires or graphite can work well.)

    Key grindings work well because they are lots of thin, short, yet elongate pieces of metal. They need to be elongate to work well, lest they just be lots of lumps not in contact with each other (I tried using steel grindings from a sharpener that my uncle used to sharpen lawnmower blades, and that was the problem with them. Not enough length-to-mass ratio).

    Mix the key grindings and the silicone, slowly adding set amounts of key grindings and mixing. You don’t want to go too high on the key grindings or it will be too difficult to stick things into the mass after it has hardened, but you do want to have enough that it is easy to mold and work with (rather than just too gooey), and enough that anywhere you stick something in it will be in contact with everywhere else. The way I tell is: I have a multimeter, and I have pieces of wire or graphite (whatever I will be sticking in). As I mix it all together, I have a big glob. I have one wire stuck in on one side, and I have another wire that I stick into several places. If I find that I can stick it in just about anywhere and there is contact, I know it’s just right. If half fail, it’s getting close and just needs a little more.

    Once the concentration of key grindings is good, I mold it into the desired shape on the desired surface (the high key grinding concentration makes it nicely moldable like play-dough), and let it cure. If I really want to make sure there’s a high chance of contact, I will even run 1-2 long copper wires underneath, molding the mix on top of them (this also increases the contact probability). OR if you want to be really sure of contact in most places, just have the whole thing on a copper plate, copper pipe, or anything conductive.

    If you want to have the whole thing down in solution, keep in mind that the key grindings (and plate, if you have a conductive plate) will have the same problem with oxidizing that all those other things you tried had (copper, silver, ect). There is, however, a fix to this as well: after your silicone-keygrinding mix has set up in the shape you want it, coat the whole thing in a layer of strait silicone. This will protect the key grindings from contact with the solution, so no oxidation will occur. Finally, whenever you stick anything into the mix (some pencil graphite, for example, dip the end you will stick in into some silicone. When you stick it into the mass, it will wad up at the top and seal the hole around it, so nothing inside comes in contact with the solution.

    You should be able to stick rigid things into this rubbery mass ad infinitum, though if you do too much poking over time you may have to add a layer of silicone to avoid exposure to the solution.

    And… I could say more, but that’s all I can think of at the moment.

  4. hot gel guy Says:

    Use Graphite; you can get rod from McMaster Carr
    Drill a hole in it, put in a piece of teflon or PFA insulated copper with conductive epoxy, pot it in RTV
    done

  5. runcyclexcski Says:

    If anyone knows a good, legit source of platinum electrophoresis wire, I would love to know. I am starting a lab, and I am thinking to put together basic agarose gel boxes myself — if it’s not too much of my time. $400 for a basic agarose box is too much

  6. reshma Says:

    can we use copper plate

  7. pastry mat Says:

    Thanks for finally writing about >Electrophoresis electrodes.
    | Cheapass Science <Liked it!

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