Frank O. Fackelmayer Frank.Fackelmayer at
Tue Nov 16 10:09:18 EST 1999

"Bernard Murray, PhD" wrote:

> In article <3830525A.A98B327C at>, james stevenson
> <pcxjs at> wrote:
> > If its gone yellow, then its decomposed.
> This is nonsense.  Clear straw-yellow MOPS solutions are just fine
> (I consider it a helpful indication that it has been autoclaved
> - although MOPS buffer will turn yellow spontaneously on exposure
> to air).

I don´t think it is nonsense to say that the yellow color of MOPS results from
its decomposition. In fact, freshly made not autoclaved MOPS is colorless (or
only very slightly yellow). As MOPS is not very stable (at -20C for several
months, at 4C approx. 4 weeks, and at RT approximately one week; info taken
from "Buffers", a booklet from Boehringer Mannheim) I assume it cannot be
autoclaved. As long as there is no other plausible explanation for the color
change upon autoclaving, I think decomposition is the most likely explanation.
BTW: Does anyone know what might cause the yellow color?

That said, I have to admit that I once used autoclaved MOPS after 2 years on
the shelf at RT (dark yellow!), and had no problems at all. Apparently
decomposition only affects a small proportion of the stuff and there is enough
intact MOPS left....


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