SDS precipitates when I add my sample to PAGE sample buffer

Han nobody at nospam.not
Sun Jun 11 12:00:31 EST 2006

Dr Engelbert Buxbaum <engelbert_buxbaum at> wrote in news:e6hfc1
$q3p$00$1 at

> 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.
Also, SDS precipitates easily in the cold, doesn't it?
Best regards
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