But you have to be aware that pH depends on the concentration of the
buffer. This is especially the case for phosphate and citrate buffer.
Daniel
Le 30/01/2014 15:51, Schnicker, Nicholas J a écrit :
It’s a pain but I usually just make each pH of whatever buffer I’m
using (if you make it concentrated then you’ll only have to do it
once). Also, if you haven’t already found it, Hampton has a nice link
to calculate volume of components while designing a tray as long as
you tell it the concentrations.
http://hamptonresearch.com/make_tray.aspx
Nick
From: Roger Rowlett <[email protected] <mailto:[email protected]>>
Reply-To: Roger Rowlett <[email protected]
<mailto:[email protected]>>
Date: Thursday, January 30, 2014 at 7:23 AM
To: "[email protected] <mailto:[email protected]>"
<[email protected] <mailto:[email protected]>>
Subject: Re: [ccp4bb] preparation of citrate buffer pH3-6.5
The easiest way to produce repeatable conditions is to titrate a stock
solution (say 1M) of citric acid with NaOH to the desired pH and use
that to mix your screen. That's what Hampton does anyway.
If fine sampling pH, you can mix various ratios of pH 3 and 6.5
buffers. The pH won't be linear with mixing ratio, but will be easily
repeatable. The actual pH of the final, magic solution can be directly
measured if desired. Calculations will never be exactly right; pKa
values are ionic strength dependent. Better to measure.
Roger Rowlett
On Jan 30, 2014 2:37 AM, "sreetama das" <[email protected]
<mailto:[email protected]>> wrote:
Dear All,
We have obtained many tiny protein crystals in a
condition containing 0.1M citric acid pH 3.5, 2M ammonium sulfate.
The crystals are too small for mounting in loops.
We intend to vary the salt concentration & pH to obtain
larger crystals.
Could anyone direct us to some links, or provide us
with a method (with calculations) to calculate the amounts of
citric acid & trisodium citrate required to obtain buffers in a
range of pH 3 - 6.5?
I have come across online buffer calculators and links
where the amounts of the components required are mentioned in
grams, but none explaining how those values were arrived at.
Thanks & regards,
sreetama
