Yellow MOPS - why?

Susanne Rohrer srohrer at
Wed Mar 22 06:36:23 EST 2000

"Hiranya S. Roychowdhury" wrote:

> At 04:49 PM 3/21/00 -0000, Wolfgang Schechinger wrote:
> >Hi all,
> >
> >I'd appreciate any explanation why our MOPS buffer  (pH 7, compsition
> >below) got yellow after autoclaving. Is this commonly observed?
> Yes, indeed!

and it does depend on how long you autoclave it.  If you take smaller bottles
it gets less yellow. it also depends on pH, because when I run a RNA gel I
don't submerge it, and the cathode and anode buffer reservoirs are separate.
the anode reservoir buffer turns clear, while the cathode side remains yellow.

> >(It's not the first time we make this buffer, but the first time it
> >got yellow. Maybe it was heated up a bit too long?)
> Everytime I autoclaved 10xMOPS buffer, it turns a straw color.
> I am not sure why this happened to you for the FIRST time!
> The degree of coloration is also directly proportional to the conc. of the
> MOPS buffer. The coloration in a 1x buffer is barely detectable, while a 20x
> stock turns yellow.
>  May we still
> >using it for northerns? The bottles used had aluminium screw caps.
> >Does this fact eventually matter? (Although I'd not assume that Al
> >is affected at this pH)

I think the MOPS is slightly oxidized. once I measured out the MOPS and the
Formaldehyde in the same cylinder and what was left turned brown after about an
hour. I think that was the Formaldehyde oxidizing the MOPS.

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