EDTA K2EDTA K3EDTA NAEDTA

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EDTA K2EDTA K3EDTA NAEDTA

Postby gene26 » May 26 2017 5:12 am

When I read literature I come across K2EDTA in phosphate buffers (why not EDTA?) for refolding, lysis...and there buffer are made with KH2PO4, K2HPO4 what is significance of K2EDTA?
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Re: EDTA K2EDTA K3EDTA NAEDTA

Postby mdfenko » May 26 2017 12:34 pm

edta, free acid, is difficult to solubilize. you have to raise the pH to about neutral or a little higher to prepare a solution.

disodium and dipotassium edta are more soluble than the free acid. they may not require neutralization to be solubilized.

the paper was telling you which neutralized form or neutralizing base was used when preparing the stocks and final solution.

as for the kh2 and k2h phosphates, they are the acidic and basic components routinely used to prepare a phosphate buffer.
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Re: EDTA K2EDTA K3EDTA NA2EDTA

Postby gene26 » May 28 2017 12:35 pm

mdfenko wrote:edta, free acid, is difficult to solubilize. you have to raise the pH to about neutral or a little higher to prepare a solution.

disodium and dipotassium edta are more soluble than the free acid. they may not require neutralization to be solubilized.


yes EDTA is hard to solubilize so it just to serve this purpose similar to Ampicillin trihydrate (MW 403.45) if I have to make 50mg/ml or 100mg/ml ampicillin solution I read I have to determine the molarity of it for Eg 50mg/ml has 123 mM and add sufficient 1M NaOH. How can I be sure that there will be 123 mM NaOH since NaOH stock concentration is 1M.

mdfenko wrote:as for the kh2 and k2h phosphates, they are the acidic and basic components routinely used to prepare a phosphate buffer


yes but why potassium normally our lab uses all sodium phosphate salts to make phosphate buffer. I observe in that paper they maintained potassium through out even with EDTA (K2EDTA instead of Na2EDTA). When to choose Na or K.
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Re: EDTA K2EDTA K3EDTA NA2EDTA

Postby mdfenko » May 29 2017 9:57 pm

gene26 wrote:yes EDTA is hard to solubilize so it just to serve this purpose similar to Ampicillin trihydrate (MW 403.45) if I have to make 50mg/ml or 100mg/ml ampicillin solution I read I have to determine the molarity of it for Eg 50mg/ml has 123 mM and add sufficient 1M NaOH. How can I be sure that there will be 123 mM NaOH since NaOH stock concentration is 1M.

you would use 123ml/liter = 123ul/ml
gene26 wrote:yes but why potassium normally our lab uses all sodium phosphate salts to make phosphate buffer. I observe in that paper they maintained potassium through out even with EDTA (K2EDTA instead of Na2EDTA). When to choose Na or K.

k-phosphate won't crystallize at refrigerator temperatures, na-phosphate can.

one reason to use one over the other is you may see ion exchange and subsequent crystallization if you use both in the same solution.

another reason is that you may have a system sensitive to one over the other.
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Re: EDTA K2EDTA K3EDTA NA2EDTA

Postby gene26 » Jun 02 2017 11:33 am

mdfenko wrote:you would use 123ml/liter = 123ul/ml


or we could simply prepare 123mM of 123ml and add it directly?

mdfenko wrote:k-phosphate won't crystallize at refrigerator temperatures, na-phosphate can.


yes I have read that 1M di sodium phosphate forms crystals at below 30C

mdfenko wrote:one reason to use one over the other is you may see ion exchange if you use both in the same solution.


Ion exchange between Na2HPO4 <---------> KH2PO4 anyway the desired pH is attained by balancing OH- and H+ is it significant whether Na+ and K+ gets exchanged?
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Re: EDTA K2EDTA K3EDTA NA2EDTA

Postby mdfenko » Jun 02 2017 11:58 am

gene26 wrote:we could simply prepare 123mM of 123ml and add it directly?


you are confusing concentration with mass. if the compound is 123mM then you'll want to match the concentration for a 1:1 concentration ratio. however, if you have 123umoles then you can add 123umoles for a 1:1 mass ratio. (i'm not sure i'm saying it in an understandable way, let me know if i'm adding to or clearing your confusion)

gene26 wrote:Ion exchange between Na2HPO4 <---------> KH2PO4 anyway the desired pH is attained by balancing OH- and H+ is it significant whether Na+ and K+ gets exchanged?

the ion exchange from k--->na will allow the phosphate to be crystallized and taken out of the solution (i have a couple of buffer references in pdf format that may be useful but can't upload them through this forum and the most useful one doesn't appear to be available anymore).
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Re: EDTA K2EDTA K3EDTA NA2EDTA

Postby gene26 » Jun 03 2017 12:40 pm

mdfenko wrote:
gene26 wrote:we could simply prepare 123mM of 123ml and add it directly?


you are confusing concentration with mass. if the compound is 123mM then you'll want to match the concentration for a 1:1 concentration ratio. however, if you have 123umoles then you can add 123umoles for a 1:1 mass ratio. (i'm not sure i'm saying it in an understandable way, let me know if i'm adding to or clearing your confusion)


I see you already did the math above it is 123ul/ml and if I had one liter of 1M solution and if I take 1ul or 50ml or 600ml the concentration in each of them is 1M right? unless I add more salt I cannot increase the molarity or by adding more water to decrease the molarity. How do I determine mass?


mdfenko wrote:i have a couple of buffer references in pdf format that may be useful but can't upload them through this forum and the most useful one doesn't appear to be available anymore


you can upload them here https://files.fm/
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Re: EDTA K2EDTA K3EDTA NAEDTA

Postby mdfenko » Jun 08 2017 11:28 am

the concentration of the aliquot itself will remain the same as the stock. it will, however, be diluted when added to another solution. mass is simply the concentration times the volume.

our firewall won't permit me onto a file sharing site. i may be able to share from my home system. i'll try later.
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