Yellow MOPS - why?

Frank O. Fackelmayer Frank.Fackelmayer at
Wed Mar 22 04:41:26 EST 2000

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?
> (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?) 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)
> composition of our MOPS buffer:
> 400 mM MOPS (morpholino ethane sulfonic acid)
> 100 mM NaOAc (sodium acetate)
> 10 mM EDTA (ethylen diamine tetra acetic acid)
> Wolfgang

Hi Wolfgang,
The question about yellow MOPS pops up every now and then on this
newsgroup, so you will find quite some info in the archives. The
take-home messages are
1. MOPS is heat labile
2. turns yellow upon autoclaving because of the chemical breakdown of
MOPS to uncharacterized substances
3. turns even more yellow (to brownish) upon storage at RT
4. the yellow color does not normally affect RNA gels, but brownish
(old) MOPS should not be used


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