EDTA K2EDTA K3EDTA NAEDTA

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May 26, 2017
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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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mdfenko 6 months ago

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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gene26 6 months ago

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.

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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mdfenko 6 months ago

you would use 123ml/liter = 123ul/ml
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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gene26 6 months ago

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

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

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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mdfenko 6 months ago

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)

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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gene26 6 months ago

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?


you can upload them here https://files.fm/

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mdfenko 6 months ago

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.