PIPES solution (How do you get the PIPES to disolve?)

Louis Hom lhom at OCF.Berkeley.EDU
Sat Mar 13 13:24:02 EST 1999

In article <36EA6910.5959 at hgu.mrc.ac.uk>,
Graham Dellaire, Ph.D. <Graham.Dellaire at hgu.mrc.ac.uk> wrote:
>I am trying to make a 100 mM solution of PIPES and for the life of me I
>can't get it into solution. Do you have to add acid or base.  I want to
>have a final solution at a pH of 6.8.  I tried heating it to 50 degrees
>etc... It just won't go into solution.

SHORT ANSWER:  ADD BASE (i.e., stick the pH probe into the solution as you
try to dissolve and pH the solution as the PIPES goes in)
*  *  *  *  *
	PIPES dissolution is, in my mind, one of _the_ great lessons in
fundamental chemical/physical equilibria (a geeky thing to say, I know,
but I guess I'm just a geek).  Anyway, there is a nice coupling of two
equilibria here:

	H-PIPES(s) + H2O <--> H-PIPES (aq)  (where H-PIPES is the free
acid form)

	H-PIPES(aq) <--> H+(aq) + PIPES-(aq)

If the solubility of H-PIPES is low (which it is, as you've seen) then
eq.1 doesn't get you very far.  So you basically have to pull eq.1 to the
right by pulling eq.2 to the right by adding base.
	It's simple and straightforward, and some folks may just say,
"well, duh!" but I think it's cool.
Lou Hom >K'93			     
lhom at ocf.berkeley.edu		

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