An interesting puzzle - Pierce's "Gentle Ag/Ab elution buffer"? <-- SOLVED

[noone]

> 
> Thanks very much to everyone who replied, to the group and by email. 
> Many people suggested it could be magnesium. Harlow & Lane "Antibodies" 
> book lists 3.5 M MgCl2 pH 7.2 as one of the alternatives to acid 
> elution. 
> 
> We ordered that stuff. It does not foam at all - so isn't detergent. It 
> does form precipitate with phopshate, which is dissolved with EDTA but 
> not EGTA, so it is Mg2+. By conductivity versus MgCl2 standards, it is 
> 3.6 M solution. NaJO4 does not oxidize anything in this solution, so I 
> don't think there is ethylene glycol present. Sooo, if anyone wants to 
> make Pierce's magic solution, the recipie is:
> 
> ~ 20 mM MES or PIPES, 
> 3.6 M MgCl2,
> titrate pH to ~ 6.5 with NaOH
> 
> Funny thing is that Pierce recommends to store this solution at 4C.
> Hehehe, like anything would grow in 3.5 M MgCl2! 
> Or is it MgCl2 unstable? :-) 
> 
> 500 ml for $65 ... from Pierce 
>         or [when buying expensive MgCl2 from Sigma] 
> 3.5 l for $104. Hmmm...


OK, but what's the brown precipitate I get from this buffer when I add
loading buffer (or any other DTT- or b-merc.-containing solution)?

Peter