SDS precipitates when I add my sample to PAGE sample buffer

Dr Engelbert Buxbaum engelbert_buxbaum at
Sun Jun 11 11:11:43 EST 2006

scott.coutts at wrote:

> The sample is prepared in PBS+5mM MgCl2 at
> pH 7.2, but after the prep the pH is about pH 10 (as is shown by
> indicator strips). The solution is clear, with no precipitated
> material. As soon as i put this in my 2xSDS-PAGE sample buffer
> (standard stuff, 2% SDS, B-ME, bromo blue) it causes the SDS to come
> out of solution. I tested that it was the SDS by adding some of my
> sample directly to a 2% SDS solution and the same thing happens.
> There's no guanidine, and no K+ salts in my sample, by the way!

Phosphate buffered saline (PBS) contains potssium. In addition, check
the solubility of SDS in the presence of bivalent metal ions like Mg,
there might be a problem too.

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