Difference between fresh 1M KCl and 1M KCl made 3 monthes ago? - (Mar/09/2008 )
Hi,
I'm working on peptide chemistry
I'm trying to fold my linear peptide ( has 6 cysteine residues) into corretly oxidativly folded form.
Optimizing best foldtion solution, I found 0.5 KCl is needed in folding solution.
The problem is ,
When I use 1M KCl solution made 3 months ago(Stored in room temperature), it folds into correctly folded form,
but when I use 1M KCl solution made freshly, it does not fold. When I check with HPLC, the peak is gone.
You may think I'm just being silly, I tried to found any other difference expect KCl . But I could not.
So I would like to ask, if there is difference between fresh 1M KCl solution, and made 3 months ago,
what could be the possible reason?
it could be contaminated.
more likely, especially since it has been stored at room temperature, there has probably been significant evaporation and it is more concentrated than fresh.
Some simple mistakes made? or like mdfenko mentioned, evaporation, esp if the volume of the solution made is small?
increase of solved CO2; compare pH of old and fresh KCl-solution
If both are supposed to be the same, and only the old one works...could it be that you made a mistake while prepearing the new one? 
Autoclaved any solutions?
No I didn't autoclaved both of them.
I'm working on peptide chemistry
I'm trying to fold my linear peptide ( has 6 cysteine residues) into corretly oxidativly folded form.
Optimizing best foldtion solution, I found 0.5 KCl is needed in folding solution.
The problem is ,
When I use 1M KCl solution made 3 months ago(Stored in room temperature), it folds into correctly folded form,
but when I use 1M KCl solution made freshly, it does not fold. When I check with HPLC, the peak is gone.
You may think I'm just being silly, I tried to found any other difference expect KCl . But I could not.
So I would like to ask, if there is difference between fresh 1M KCl solution, and made 3 months ago,
what could be the possible reason?
Thank you for your comments, Maybe I could have made mistakes making KCl solution, but it seems there's other reason.
I'm suspecting carbon dioxide, and I'm trying some test. If I get the answer why there's difference, I will tell you. Thanks,
It always good to include some buffer components to maintain the pH.
I guess the 1M KCl is diluted in a buffered solution... Then, I can't imagine that the slight difference in the pH of the old vs the new could inducte a pH change in the final solution ?!
Hope you will find the answer.
ggod luck