Bill, You still lose a point for missing
the fourth pKa in ammonium citrate, the
ammonium ion.
Kind regards, Pete
-----Original Message-----
From: CCP4 bulletin board on behalf of William G. Scott
Sent: Sat 8/9/2008 12:09 PM
To: [log in to unmask]
Subject: Re: [ccp4bb] Ammonium citrate tribasic buffer
Well, as long as I was right. That is the important thing. ;)
William G. Scott
Contact info:
http://chemistry.ucsc.edu/~wgscott/
On Aug 9, 2008, at 11:11 AM, Ian Tickle wrote:
>
> I think the problem is that Britannica, or even Wikipedia, is and
> has never been the final arbiter of truth, I would put my faith in a
> specialist publication such as:
>
> http://books.google.co.uk/books?id=bwbCVCFPNI4C&pg=PA175&lpg=PA175&dq=%22karl+hasselbalch%22&source=web&ots=yHzTUiNE1g&sig=7JmNU-OfHIkmXxR5ivGTrpS7_Us&hl=en&sa=X&oi=book_result&resnum=5&ct=result
>
> -- Ian
>
>> -----Original Message-----
>> From: [log in to unmask]
>> [mailto:[log in to unmask]] On Behalf Of William Scott
>> Sent: 07 August 2008 23:27
>> To: Juergen Bosch
>> Cc: [log in to unmask]
>> Subject: Re: [ccp4bb] Ammonium citrate tribasic buffer
>>
>> Wikipedia claims Hasselbach is a misspelling:
>>
>> http://en.wikipedia.org/wiki/Henderson-Hasselbalch_equation
>>
>> Since Wikipedia has now replaced the social consensus as the final
>> arbiter of truth ...
>>
>>
>> On Aug 7, 2008, at 3:22 PM, Juergen Bosch wrote:
>>
>>> Just on a side note, can someone clarify why Hasselbach is not
>>> Hasselbalch or vice versa ? Or is that the same guy just somewhere
>>> sometime misspelled and for ever in the records ?
>>>
>>> See here:
>>>
>> http://www.britannica.com/EBchecked/topic/261188/Henderson-Has
> selbach-equation
>>>
>>> Jürgen
>>>
>>>
>>> On 7 Aug 2008, at 15:12, [log in to unmask] wrote:
>>>
>>>> Good points!
>>>>
>>>> Not only citrate is inappropriate for buffers in the pH 6.5-7.5
>>>> range,
>>>> but also (as pointed out by your colleagues at UCSC, but
>> probabbly
>>>> elsewhere,
>>>> polyprotic acids are hard to handle, as their pKa change in a
>>>> significant
>>>> fashion depending on their concentration.
>>>>
>>>> In this case, the Henderson-Hasselbalch equation must be
>> written in
>>>> terms
>>>> of activities rather than concentrations, otherwise it is totally
>>>> useless.
>>>>
>>>> Nadir Mrabet
>>>>
>>>>
>>>>
>>>> Selon "William G. Scott" <[log in to unmask]>:
>>>>
>>>>> There are 3 pKa's for citric acid:
>>>>>
>>>>> 3.15, 4.77, and 5.19
>>>>>
>>>>> so it is going to be a lousy buffer at pH 6.7 to 7.25.
>> Also, you
>>>>> need
>>>>> to know what concentration your buffer is, and whether that
>>>>> concentration is with respect to the citrate ion or what. It
>>>>> won't be
>>>>> tribasic with respect to ammonium ion near neutral pH.
>>>>>
>>>>> So if for example you need 1M of this buffer, the simplest thing
>>>>> to do
>>>>> is make up a 1M stock solution of tribasic ammonium
>> citrate and a 1M
>>>>> stock solution of of citric acid and then mix the two
>> together. You
>>>>> can calculate the ratio using the Henderson-Hasselbalch
>> equation or
>>>>> just titrate one into the other while stirring in the
>> presence of
>>>>> a pH
>>>>> electrode.
>>>>>
>>>>> (You'll have to use the pH electrode approach if you took
>>>>> introductory
>>>>> chemistry from anyone other than me at UCSC since my colleagues
>>>>> think
>>>>> that polyprotic acids are too stressful for our undergrads.)
>>>>>
>>>>>
>>>>> William G. Scott
>>>>>
>>>>> Contact info:
>>>>> http://chemistry.ucsc.edu/~wgscott/
>>>>>
>>>>>
>>>>> On Aug 7, 2008, at 12:42 PM, E rajakumar wrote:
>>>>>
>>>>>> Dear All
>>>>>> Sorry for non crystallographic query.
>>>>>> Can any body mail me how to prepare Ammonium citrate
>>>>>> tribasic (citric acid triammonium salt) buffer pH 6.7
>>>>>> to 7.25 and also what is the pKa value.
>>>>>> Thanking you in advance
>>>>>> Rajakumara
>>>>>>
>>>>>>
>>>>>>
>>>>>> E. Rajakumara
>>>>>> Postdoctoral Fellow
>>>>>> Strcutural Biology Program
>>>>>> Memorial Sloan-Kettering Cancer Center
>>>>>> New York-10021
>>>>>> NY
>>>>>> 001 212 639 7986 (Lab)
>>>>>> 001 917 674 6266 (Mobile)
>>>>>>
>>>>>>
>>>>>>
>>>>>> Get your new Email address!
>>>>>> Grab the Email name you've always wanted before
>> someone else
>>>>>> does!
>>>>>> http://mail.promotions.yahoo.com/newdomains/aa/
>>>>>
>>>>
>>>>
>>>> Pr. Nadir T. Mrabet
>>>> Cellular & Molecular Biochemistry
>>>> INSERM U-724
>>>> UHP - Nancy 1, School of Medicine
>>>> 54505 Vandoeuvre-les-Nancy Cedex
>>>> France
>>>> Tel : +33 (0)3.83.68.32.73
>>>> Fax : +33 (0)3.83.68.32.79
>>>> E-mail : [log in to unmask]
>>>
>>> -
>>> Jürgen Bosch
>>> University of Washington
>>> Dept. of Biochemistry, K-426
>>> 1705 NE Pacific Street
>>> Seattle, WA 98195
>>> Box 357742
>>> Phone: +1-206-616-4510
>>> FAX: +1-206-685-7002
>>> Web: http://faculty.washington.edu/jbosch
>>
>>
>
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