Stephen R. Lasky Ph.D. wrote:
>In article <voeller-0212950659470001 at voeller.his.com>, voeller at his.com>(Jim Voeller) wrote:
>>> If I can add something here. I know that every source says to use fresh
>> APS, but......I make 10% APS and freeze single use aliquots at -20 and it
>> works forever! Well I haven't tested the forever part but it works for at
>> least 6 months. Try it.
>> Jim Voeller
>>voellerj at gunet.georgetown.edu>> Lombardi Cancer Center, Georgetown University
>> Washington DC, USA
>>Jim, you've been lucky. When I was a grad student I tried doing the same
>thing you describe. After a run of failed gels just when I was trying to
>finish off a paper, I traced the problem back to the APS. I make it fresh
>every time now and teach my students and postdocs to do the same. After
>all, how hard is it to make a 10% APS solution? Dump some APS out an a
>weigh paper, see what it weighs, add enough water to make 10% and mix.
>Takes about as long as defrosting a tube of frozen APS.
<the rest deleted>
Yes, I'm also lucky and was lucky many years using APS stored at -20 C. I
use 30 % APS. The aliquot currently in use I keep in the freezing department
of the common +4 C refrigerator.
It's less hard to defrost frozen solution than to make new for me. But I
understand you Stephan too: to teach others to make solution takes much less
pain than to teach to make, to freeze and to defrost the solution.
There is very simple, reliable and sensitive method for determining quality
of APS solutions. The decay of APS necessary results in ammonium
hydrosulfate, therefore APS solutions acidify as a result of persulfate
cleavage and you can test it by pH indicator paper. This test differs from
the other ones proposed in this discussion because it measures the
degradation products, not remaining persulfate (and therefore they detect
only complete disappearing of APS). From practical point of view it is very
sensitive, because hydrosulfate is a strong acid, and even 10 mM lowers pH
till 2. 10 % APS is about 500 mM, so you will detect even very low extent of
the degradation, e.g. during storage at +4 C for several weeks. If you find
it too sensitive, you may consider the way how the color changes when the
solution is applied on pH paper. If only the location where the drop was
applied changes color to 'acid' , and the solution soaking into the paper
does not change the color to 'acid', this means that conc. of acid is low
and the solution is still good for PAGE.
Dept. of Biochem. and Biophys., Vilnius University, Lithuania
Rimantas.Plaipa at GF.VU.LT