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Alternatively you could make a stock solution of citric acid (say 1 M for example) and stock solution of sodium citrate (also 1 M). Mix them in the appropriate ratio to ballpark the right pH and just adjust up or down with the stock solution. The concentration of citrate will be the same no matter the final volume. You can then dilute that down to whatever your final concentration of citrate needs to be. If you are looking for the actual method to do the calculations I would suggest finding a chemistry textbook and looking at the chapter on buffering and the Henderson-Hasselbalch equation. Cheers, Katherine On Thu, Jan 30, 2014 at 9:31 AM, Daniel Picot <[log in to unmask]> wrote: > 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 <[log in to unmask]> > Reply-To: Roger Rowlett <[log in to unmask]> > Date: Thursday, January 30, 2014 at 7:23 AM > To: "[log in to unmask]" <[log in to unmask]> > 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" <[log in to unmask]> 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 >> > > -- "Nil illegitimo carborundum"* - *Didactylos