Chemical Forums
Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: Optimist on June 25, 2017, 09:30:44 PM
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How can I prepare the 01M triethylammonium phosphate buffer of pH 2.8~~~~.
I know this can be prepared by using triethylamine (TEA) and phosphoric acid and in my Lab I have Triethylamine and 85% phosphoric acid. I actually search a lot and I able to find the preparation of TEAA ( triethylammonium acetate buffer of pH ~~~7.4) but couldn't able to find any reference of TEAP buffer.
what I understand from that, first I have to prepare the 01M triethylamine and I have to adjust the pH of solution to ~2.8 using phosphoric acid?
But I have question when I will add the phosphoric acid the concentration of solution will change and it will not be anymore 1M TEA.
Kindly help me with procedure how to prepare that TEAP buffer?
Thanks in advance. ::)
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0.1 M in TEA or 0.1 M in phosphates?
How precisely 0.1 M? 0.10 M, or will 0.11 M or 0.90 M do?
In general - no magic here, sounds like a rather standard buffer preparation, requiring you to calculate initial amounts of acid and base required with Henderson-Hasselbalch equation (assuming TEA to be fully protonated). It won't be easy, as the IS of the solution is quite large here. I would start with the Buffer Maker (http://www.chembuddy.com/?left=Buffer-Maker&right=buffer-calculator) - but even then depending on how precise you have to be you may need some experimenting to find a prefect recipe.
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Actually, I want to prepared 0.05M Triehtylammonium phosphate (TEAP) buffer of pH 2.8 which i want to use reverse phase HPLC analysis of sample. I actually need this in liters. therefore, first I am preparing stock solution of 1M TEAP and when ever i need for HPLC analysis I can make the dilution and subsequently will use for HPLC.
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OK. Triethylamine has a pKa of 10.78 at 25 deg C.
Your pH of 2.8 is very far away.
You are not preparing a buffer. You are not preparing a buffer. A buffer is not what you're preparing, and this thing, that you're preparing, is not a buffer.
Sorry, I felt I had to be crystal clear. Feel free to call it a buffer if you feel like it, I always do. I'm just defending you from someone pedantic.
You need pH 2.8? No problem -- weigh or measure more TEA than you will need, stir it in water (it won't dissolve), then add 85% phosphoric acid until it dissolves and is the correct pH, then add water until the volume gives you 1 M TEAP. You will have stock solution, that you can dilute further for 0.05 M.
You will not have a buffer. (Did I mention that? Humph, sounds like I heard it somewhere before.) You will have a solution of dilute phosphoric acid at 0.1 M TEAP. If this is what your protocol calls for, this is what they mean. Edit: I'm just reiterating what Borek: said here.
Please be certain you're not mis-reading your protocol. This low pH will quickly strip the bonded phase off of a silica column. Your concentration is quite low -- are you doing mass spec detection? Because even faint traces of stripped off bonded phase will wreak havoc with the mass spec. Unless you're not using a bonded to silica column.
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I have seen few reference they called it TEAP buffer which may be misleading.
I want to use preparative reverse phase HPLC (gradient elution) to check the purity of sample. I found one protocol ( Methanol and 0.05M TEAP buffer) and as you mentioned about working at low pH would likely strip the bonded phase of silica column. Keeping this thing in mind I checked my column, it's Water XTerra Hybride particle technology, containing inorganic ( silica) and organic (organosiloxane).
As they mentioned that XTerra columns have a widened usable pH range (2-12 for RP columns) over silica based columns,
But i am not sure about my column, is it silica based column?
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Most definitely, the Xterra column is silica based. However, the advanced technology is better than traditional columns at surviving this extreme pH. I would include a rinse at the end of the day of water and solvent to maximize column lifetime. Waters won't tell you that, they want you to keep buying columns. ;D
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Thank you for such a nice comment Arkcon,
Stay blessed.!!!!!!!!
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1 M triethylamine is not miscible in water, but it can be brought into solution when it is protonated, based upon my experiences making triethylammonium bicarbonate buffer. Therefore, I would add distilled TEA drop-wise to phosphoric acid until I obtained the correct pH. The first pKa of phosphoric acid is roughly 2; therefore, you will have a little bit of buffer capacity from the first dissociation of phosphoric acid. Just a WAG but perhaps the TEAH+ is needed as a counter-ion?
I cannot speak to the question of how the silica will take to this particular reagent. However, I was taught to rinse out TFA-based mobile phases after using reversed-phase columns. TFA is trifluoroacetic acid.
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OK. Triethylamine has a pKa of 10.78 at 25 deg C.
Your pH of 2.8 is very far away.
You are not preparing a buffer. You are not preparing a buffer. A buffer is not what you're preparing, and this thing, that you're preparing, is not a buffer.
Perhaps I am missing something, but if you use TEA to neutralize part of the phosphoric acid you end at pH 2.8 with a solution containing protonated TEA (which is just a counterion) and a buffer composed of H3PO4 and H2PO4- (pKa of 2.2). So IMHO it is definitely a buffer, just not TEA based, but a phosphoric one (the name is misleading).
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Borek,
That is what I was trying to say, but I did not say it as clearly as you did. I think that some HPLC systems use the triethylammonium ion as a ion-pair reagent, but I don't have any references handy.
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Borek & Babcock_Hall
I am using this TEAP as ion paring reagent because my compound is basically complex of metal ion with positive charge on it.
I prepared 1M TEAP (buffer) ion paring reagent by first adding TEA (14ml) in to the water( which is obvious not miscible with water) and then phosphoric acid was added dropwise under in ice bath until pH reaches 2.8, and finally makeup volume to 100ml.
Is this a right procedure or first I have to add phosphoric acid in water first and then adjust pH 2.8 using TEA.?
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If the final solution has a correct pH and a correct concentration of TEA*, procedure doesn't matter much. Some approaches are easier, some are more difficult, some are safer, but in the end it is the result that counts.
*(note: you have still not addressed the question I asked at the very beginning - 1 M in what should the solution be, it can't be 1 M in "buffer")
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Optimist,
Does the overall complex have a negative charge?
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Borke,
I just want to prepare 0.05M TEAP buffer from 1M TEAP stock solution.
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Babcock_Hall
No, The complex have overall positive charge and it is lipophilic in my opinion.
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I just want to prepare 0.05M TEAP buffer from 1M TEAP stock solution.
You are still missing the point and I am starting to doubt you understand what the buffer is and how it works.
Buffer you need is made by neutralizing phosphoric acid and contains HTEA+ (protonated amine) and H3PO4 and H2PO4- in a ratio given by the Henderson-Hasselbalch equation, approximately
[tex]\frac {[H_3PO_4]}{[H_2PO_4^-]} = 0.2[/tex]
For obvious reasons concentrations of HTEA+ and H2PO4- are identical.
In this context saying "1 M solution" doesn't mean anything without saying which substance is 1 M. In the case of buffers we often say "1 M buffer" meaning "sum of concentrations of the acid and conjugate base equals 1 M" - so in this case your stock solution would be 1 M in phosphates and about 0.17 M in TEA. Do you see why "1 M TEAP buffer" means nothing and is ambiguous?
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Hello, Borek
Buffer is the a mixture of weak acid and its salt ( conjugate base or conjugate acid , respectively) that premits solution to resist change in pH.
In Henderson-Hasselbalch equation if the concentration of weak acid is equal to that of conjugate base, the ratio of two component is one. So, pH=pKa because the log(1)=0. In this case solution is know as best buffer.
To be honest in this case I didn't get your point, it's little confusing when I am preparing TEAP buffer.
Kindly would you help me in that case. Actually I need 0.05M TEAP buffer or solution for my HPLC analysis
Regards,
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Let's start with something simple, examples are best approach to such problems.
Acetic acid has pKa = 4.75, so the buffer prepared from equimolar amounts of acetic acid and sodium acetate has pH is 4.75.
Please try to calculate what are concentrations of: acetic acid, acetate anion, Na+ in 1 M acetate buffer of pH=4.75.
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Answer:
Acetic acid concentration = 0.5 mole
Acetate anion concentration= 0.5 mole
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Then it is 0.5 M in Na+, isn't it?
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yes, you are right 0.5 Na+
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So why is it 1 M buffer?
Or, to ask the same question I asked long ago - it is a buffer 1 M in what?
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0.1 M in TEA or 0.1 M in phosphates?
Protocol haven't mentioned about 0.1 M in TEA or 0.1 M in phosphate. it's just 0.1 M TEAP buffer.
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So why is it 1 M buffer?
Or, to ask the same question I asked long ago - it is a buffer 1 M in what?
It is 1 M buffer in 0.5 M Phosphate I think ? isn't ?
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So why is it 1 M buffer?
Or, to ask the same question I asked long ago - it is a buffer 1 M in what?
It is 1 M buffer in 0.5 M Phosphate I think ? isn't ?
So you are starting to see why it is problematic to state "1 M TEAP buffer"?
As I told you from the very beginning - such a statement is ambiguous.
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Borek
Now I catch up what you want to say!! but anyway my HPLC protocol called it 0.05 M TBAP buffer, for time being so Let's supposed it as buffer
Still I have problem related with HPLC column, I am not getting any peak while performing HPLC analysis of my sample. I am using Water XTerra Hybride particle technology, containing inorganic ( silica) and organic (organosiloxane) column. The actual protocol ( I have seen different reference of the sample I am analyzing) used Beckman C18 RP ultrasphere Octyladecyl silane column.
What is the difference between two column? Both are RP C18.
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Now I catch up what you want to say!! but anyway my HPLC protocol called it 0.05 M TBAP buffer, for time being so Let's supposed it as buffer
It is a buffer, there is just not enough information to prepare it.
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What about second part my question. ? the column are they same or different?