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 <rrowl...@colgate.edu<mailto:rrowl...@colgate.edu>> Reply-To: Roger Rowlett <rrowl...@colgate.edu<mailto:rrowl...@colgate.edu>> Date: Thursday, January 30, 2014 at 7:23 AM To: "CCP4BB@JISCMAIL.AC.UK<mailto:CCP4BB@JISCMAIL.AC.UK>" <CCP4BB@JISCMAIL.AC.UK<mailto:CCP4BB@JISCMAIL.AC.UK>> 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" <somon_...@yahoo.co.in<mailto:somon_...@yahoo.co.in>> 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
