Midi-preps

[Michael Coyne]

In article <1993Sep21.151134.160 at ntet.nctr.fda.gov>,
wmelchior at ntet.nctr.fda.gov (Bill Melchior) wrote:

> In article <1993Sep20.212825.17557 at ohsu.edu>, nishir at ohsu.edu writes in 
> part:
> 
> > Solution II (good for about 2 weeks)              
>               ^^^^^^^^^^^^^^^^^^^^^^^^ 
> > To make 100 mls: 
> >    0.8 g NaOH (0.2 M) 
> >    10 mls 10% SDS (1%) 
> 
> Plasmid protocols frequently call for making this fresh (eg, Maniatis et
> al).  I, on the other hand, haven't seen any problems with a solution well
> over a year old (stored in a polythylene bottle as suggested by Kieser in
> Plasmid 12:19-36, 1984, who does NOT suggest making it fresh).  Birnboim,
> Meth. Enz. 100:243-255, 1983, says, "The shelf life at room temperature is
> about a week or longer, depending upon the source of SDS; ...."  I'd like
> to know if nishir or anyone else has actually had bad experiences with old
> alkaline SDS, or is it just folklore?  What happens when the solution goes 
> bad?
> 
> Comments welcomed; Bill


There is, however, the question of how companies (like Promega) can supply
min-prep kits (like Wizard) if the shelf-life of one of the reagents
(NaOH/SDS) is only two weeks.  Their product's cell lysis solution is 0.2M
NaOH and 1% SDS, no additives listed, and they guarantee the product for
"at least six months from the date of purchase....".  Note that that's date
of *purchase*, not date of manufacture or some date stamped on the box. 
Who knows how long ago the kit was actually manufactured (though I suspect
not too long of a time elapses between manufacture and sale - probably a
couple of weeks to a month).  But, we're talking about a reagent with a
supposed shelf life of only two weeks....

Hmmm...  Lab Myth?

Mike