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buffer ph


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#1 agronl

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Posted 26 December 2010 - 03:04 AM

in the following buffer
100 ml 1 M Tris-HCl pH 7.5
20 ml 500 mM EDTA pH 8.0
880 ml ultra pure water

Why every component is described with deferent ph and not all together the final ph?

#2 phage434

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Posted 26 December 2010 - 06:55 AM

Because you probably have somewhere on the shelf bottles of 1M Tris-HCl pH 7.5, and bottles of EDTA 500 mM pH 8.0. Mixing them together in the proper proportions is easy. If you don't have those bottles on the shelf, I'd recommend either buying or making them. You'll need them for other things.

#3 agronl

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Posted 26 December 2010 - 08:16 AM

Tris HCL has ph 9 and EDTH ph 4
If you mix them you need only to adjust with NaOH (not much)
If you first adjust Ph of Tris you have to add a lot of HCl
And then after you add EDTH a lot of NaOH

#4 mdfenko

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Posted 30 December 2010 - 07:23 AM

Tris HCL has ph 9 and EDTH ph 4
If you mix them you need only to adjust with NaOH (not much)
If you first adjust Ph of Tris you have to add a lot of HCl
And then after you add EDTH a lot of NaOH

tris base has a pH ~10.4 (0.1M solution) when not adjusted (tris-hcl, the acid component, has a pH ~4.7 at 0.1M).

edta, free acid, will not significantly solubilize until the pH is ~8.

the formulation that you give in the original post is using stock solutions of tris and edta that have been titrated to the pH indicated. after mixing the amounts indicated and adjusting to final volume, the pH will be ~7.5 due to the buffering properties of the tris.

if you add powders of both, as indicated by your second post, then you will need to adjust the pH to 7.5 prior to adding water to the final volume. you may have to overshoot towards pH 8 to ensure complete solubilization of the edta and then adjust back down to 7.5.
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#5 agronl

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Posted 30 December 2010 - 08:06 AM


Tris HCL has ph 9 and EDTH ph 4
If you mix them you need only to adjust with NaOH (not much)
If you first adjust Ph of Tris you have to add a lot of HCl
And then after you add EDTH a lot of NaOH

tris base has a pH ~10.4 (0.1M solution) when not adjusted (tris-hcl, the acid component, has a pH ~4.7 at 0.1M).

edta, free acid, will not significantly solubilize until the pH is ~8.

the formulation that you give in the original post is using stock solutions of tris and edta that have been titrated to the pH indicated. after mixing the amounts indicated and adjusting to final volume, the pH will be ~7.5 due to the buffering properties of the tris.

if you add powders of both, as indicated by your second post, then you will need to adjust the pH to 7.5 prior to adding water to the final volume. you may have to overshoot towards pH 8 to ensure complete solubilization of the edta and then adjust back down to 7.5.






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