Jump to content

  • Log in with Facebook Log in with Twitter Log in with Windows Live Log In with Google      Sign In   
  • Create Account

Submit your paper to J Biol Methods today!
Photo
- - - - -

Is there a buffer at acidic pH? (pH 1 and 2)

buffers acidic pH pH 1 pH 2

Best Answer mdfenko, 05 September 2013 - 03:49 AM

depending on which way you need to resist change in pH (toward more acidic or more basic, buffering is best at pK+ or -1.0 pH unit):

 

pyrophosphate has pK1=0.9; pK2=2.0 you can use it for both pHs

 

phosphoric acid has pK1=1.0

 

oxalic acid pK1=1.2

 

histidine and maleic (not malic) acid both have pK1=1.8

 

aspartic and glutamic acid both have pK1=2.1

 

lysine has pK1=2.2

 

glycine has pK1=2.4

 

let us know if you require any other suggestions

Go to the full post


  • Please log in to reply
22 replies to this topic

#16 El Crazy Xabi

El Crazy Xabi

    Veteran

  • Active Members
  • PipPipPipPipPipPipPipPipPipPip
  • 194 posts
20
Excellent

Posted 26 September 2013 - 05:50 PM

KCl/HCl is one of the few buffers for pH 2 or below, if not the only one, that are commonly listed. Indeed HCl itself wouldn't make any sense as buffer unless you go to pH -7... in theory... in a depreciable ionic strength system. Good point Borek, I didn't realise initially, I was starting to think about the ionic strength too.
Adding a chloride (KCl), though you may add NaCl, LiCl,... being equally suitable for this, increases even more the ionic strength of the system. Common ion effect applied to buffers.

 

KCl/HCl buffer is probably not used to keep anything alive but as far as I know it is used in enzymology and biochemistry in general.



#17 mdfenko

mdfenko

    an elder

  • Active Members
  • PipPipPipPipPipPipPipPipPipPip
  • 2,710 posts
123
Excellent

Posted 27 September 2013 - 04:30 AM

ionic strength is a combination of the ion and counter-ion. 0.1M hcl would have an ionic strength of 0.2M.

 

a polyprotic acid, such as phosphoric acid (3 ionizable hydrogens), would be able to present 0.1M hydrogen ions with a counter ion concentration of ~0.033M. the ionic strength of this buffering system (ignoring any other components of the medium) would be 0.133M. sulfuric acid (2 ionizable hydrogens) would be able to present 0.1M hydrogen with a total ionic strength of 0.15M.

 

as for literature regarding commonly used biological buffers, i already posted some. on the other hand, it is unusual to work at such a low pH in biological systems (unless you are working with acidophiles).


Edited by mdfenko, 27 September 2013 - 04:33 AM.

talent does what it can
genius does what it must
i do what i get paid to do

#18 Borek

Borek

    member

  • Active Members
  • Pip
  • 13 posts
0
Neutral

Posted 27 September 2013 - 12:54 PM

KCl/HCl is one of the few buffers for pH 2 or below, if not the only one, that are commonly listed

 

I always wonder when I see such recipes if they were not designed blindly by someone not understanding what it is all about. Like - buffer is made by mixing acid and salt, let's mix acid and salt to get a pH 1.0 buffer. KCl presence doesn't change anything - with, or without it, solution has exactly the same buffering capacity. KCl only increases the ionic strength. Could be it has some other properties, but I have no idea what purpose it can serve.



#19 Borek

Borek

    member

  • Active Members
  • Pip
  • 13 posts
0
Neutral

Posted 27 September 2013 - 01:09 PM



ionic strength is a combination of the ion and counter-ion. 0.1M hcl would have an ionic strength of 0.2M.

 

By definition ionic strength is half of the sum of concentrations of all ions multiplied by their charges squared - see http://en.wikipedia..../Ionic_strength or another ionic strength discussion (or any other source). I remember reading that it was defined this way to make ionic strength equal concentration for 1:1 electrolytes.That means for 0.1M HCl ionic strength is 0.5*(0.1*12 + 0.1*12) = 0.1. 

 


 

a polyprotic acid, such as phosphoric acid (3 ionizable hydrogens), would be able to present 0.1M hydrogen ions with a counter ion concentration of ~0.033M. the ionic strength of this buffering system (ignoring any other components of the medium) would be 0.133M. sulfuric acid (2 ionizable hydrogens) would be able to present 0.1M hydrogen with a total ionic strength of 0.15M.

 

You are ignoring squaring of the charges. For triprotic acid ionic strength would be 0.5*(0.1*12 + 0.033*32) = 0.1985, for diprotic acid ionic strength would be 0.5*(0.1*12 + 0.05*22) = 0.15 (which is accidentally the same value you got). Both solutions have ionic strength higher than 0.1.

 

 


as for literature regarding commonly used biological buffers, i already posted some

 

None of the two documents you posted addresses the problem. One of them lists HCl/KCl buffer for pH 1.0 (see my post above), but doesn't say anything about whether using just HCl is wrong (and if - why).


Edited by Borek, 27 September 2013 - 01:12 PM.


#20 mdfenko

mdfenko

    an elder

  • Active Members
  • PipPipPipPipPipPipPipPipPipPip
  • 2,710 posts
123
Excellent

Posted 07 October 2013 - 05:45 AM

(i learned a little bit more about calculating ionic strength, thanks)

 

i would guess, then, that the primary reason to use a polyprotic buffer salt is that you can maintain pH with a lower molarity than with a monoprotic "buffer" (buffering capacity).

 

on the other hand, using straight hcl with proteins (if that's the purpose of the medium) may endanger the peptide bonds and certain amino acids (hcl is used to hydrolyze peptide bonds for amino acid analysis, albeit at higher concentrations).


Edited by mdfenko, 07 October 2013 - 05:46 AM.

talent does what it can
genius does what it must
i do what i get paid to do

#21 El Crazy Xabi

El Crazy Xabi

    Veteran

  • Active Members
  • PipPipPipPipPipPipPipPipPipPip
  • 194 posts
20
Excellent

Posted 07 October 2013 - 07:38 PM

as for literature regarding commonly used biological buffers, i already posted some. on the other hand, it is unusual to work at such a low pH in biological systems (unless you are working with acidophiles).

Actually, acidophiles wouldn't be very happy with that buffer. In general they are pretty sensitive to anions other than sulfate (or selenate due similarity), being chloride quite toxic.

 

 

on the other hand, using straight hcl with proteins (if that's the purpose of the medium) may endanger the peptide bonds and certain amino acids (hcl is used to hydrolyze peptide bonds for amino acid analysis, albeit at higher concentrations).

For aa analysis you use really high HCl concentration and under high temperature, nearly as done for mineral analysis.
The buffer is common use to determine stability and activity of enzymes at the buffer pH range (1.0-2.2)



#22 Borek

Borek

    member

  • Active Members
  • Pip
  • 13 posts
0
Neutral

Posted 08 October 2013 - 02:42 AM



(i learned a little bit more about calculating ionic strength, thanks)

 

You are welcome :)

 

 


 

i would guess, then, that the primary reason to use a polyprotic buffer salt is that you can maintain pH with a lower molarity than with a monoprotic "buffer" (buffering capacity).

 

 

Now that I think about it - lower osmolality for sure. Still, if that's what you want, you don't need a salt, you can use just a strong polyprotic acid. Comparing pH 1.00 solutions of hydrochloric acid and sulfuric acid:

 

                                       HCl              H2SO4

molarity                           0.155           0.135

ionic strength                  0.155           0.197

buffering capacity           0.402           0.461

osmolality                        0.200           0.171

 

(these are calculated using Davies equation, I can give more details if someone wants to reproduce these results).

 

 


 

on the other hand, using straight hcl with proteins (if that's the purpose of the medium) may endanger the peptide bonds and certain amino acids (hcl is used to hydrolyze peptide bonds for amino acid analysis, albeit at higher concentrations).

 



 


as for literature regarding commonly used biological buffers, i already posted some. on the other hand, it is unusual to work at such a low pH in biological systems (unless you are working with acidophiles).

Actually, acidophiles wouldn't be very happy with that buffer. In general they are pretty sensitive to anions other than sulfate (or selenate due similarity), being chloride quite toxic.

 

As I already wrote earlier - while HCl has its obvious advantages, I used it only as an example in calculations, I never suggested it is the best possible acid to use. Just sulfuric acid would work as well - it would even have slightly higher buffering capacity due to the presence of HSO4-/SO42- system (at pH 1.0 ratio of concentrations HSO4-/SO42- is about 3:1). 

 

I guess that when it comes to peptide bonds hydrolysis HCl is just a perfect source of H+ that do the job, counterion is most likely not that important. I doubt peptide bonds would be much safer in any other solution with comparable pH.



#23 mdfenko

mdfenko

    an elder

  • Active Members
  • PipPipPipPipPipPipPipPipPipPip
  • 2,710 posts
123
Excellent

Posted 08 October 2013 - 11:16 AM

at a pH of 1 the buffer "salt" would be mostly (if not completely) acid. there may be some counterion to fine tune the pH, if necessary.

 

chlorine ion will attack certain amino acids, so choice of counterion (or, in this case, buffering ion) is important.


talent does what it can
genius does what it must
i do what i get paid to do





Home - About - Terms of Service - Privacy - Contact Us

©1999-2013 Protocol Online, All rights reserved.