6M Guanidinium HCl solution

[pfluffernuugen]

I need to make a series of 6M and 8M guanidinium HCl buffers for a protein purification, but I can't seem to get the GdnHCl into solution. I'm able to make a clear 8M solution, but when I make the 6M solution, theres some sort of cloudy precipitate that eventually settles.

 

I've tried using the 8M solution as a stock and diluting it down to 6M, but I've noticed that it starts to crash out at around 7.3M. Heating it to 35C doesn't make a difference, nor does stirring it for several days.

 

Is there some trick to it or has my GdnHCL probably gone bad?

[CharonY]

This is weird. Normally you have to slightly heat the solution to around 37 C to prepare the 8M solution. The 6M should work fine on RT. The reverse does not make much sense to me. Is the water you are using OK?

[pfluffernuugen]

The water should be fine. It's from a milliQ system with a measured resistance of around 18MOhm

[CharonY]

Then I am out of ideas. Maybe you should check the pH of the solutions. But quite frankly I would not know why a higher concentration should have less impact than a low one.