Re: [DIYbio] Re: Paper electrophoresis... super available molecule separation?

On Wed, Jan 30, 2013 at 6:55 PM, John Griessen <john@industromatic.com> wrote:
> On 01/30/2013 05:49 PM, Nathan McCorkle wrote:
>>
>> But DNA migration depends on the e-field not on the power through it
>
>
> Sure, that's true. And I was talking about the e-field also.
> Ohms per square are the Ohms that resist the e-field. Look it up.

I'm not sure why you're mentioning current or the resistance of the
media, or what you want me to look up.

You only want to keep current low enough such that the media doesn't
become too hot, and that depends on ion (salt and buffer)
concentrations.

>
> The aspect ratio of an electrophoresis path determines how conductive it is
> if all other variables are the same, (salts, buffers, conductive stuff in
> solution,
> gooeyness, amount of duct tape used, viscosity, Coriolis effect, what have
> you)

Sure that's going to reduce the overall current, that's a good thing.
Automated Sanger sequencing systems use 50 micron capillaries to do
electrophoresis.

310 Capillary, 61cm x 50µm (50 cm well-to-read) - for sequencing
applications. Internally uncoated. 2 capillaries/package (100
runs/capillary).
https://products.appliedbiosystems.com/ab/en/US/adirect/ab?cmd=catProductDetail&productID=402840&catID=602042&backButton=true


> In short, neglect the rest, take the ohms per square analysis to get to the
> heart of designing any new shape relative to a usual gel box.
>
> How you reduce it to a 2D problem from a 3D world is to find the
> conductivity of a cube,
> then map that onto your path layout in 2D and consider it a uniform layer
> that can be treated
> as X,Y movement only, neglecting Z axis, and you're to a 2D representation
> that can
> simplify and give you design insights.
>

You'd probably get close just using the analytical concentration of
the buffer, then stick an ohm meter on the electrodes.

But if you have a voltage controlled power supply, then you just worry
about Volts per distance?

Are we on the same page?


--
-Nathan

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