I have the salt for making the MES buffer ( 2-(N-morpholino)ethanesulfonic acid ) and 0.1M solution of it give me a PH of almost 7 which I have found out it's due to the DI water( I used to make the buffer) that has a pH 8.45.
Considering this fact that it's not possible for me to change the water, could I use the Hydrochloric acid to regulate the pH to 6?
Dear Arezoo:
Considering that (at least according to the SIGMA Technical Data Sheet) MES buffer solution - depending on its concentration - yields pH-values between 2.5 and 5.0 and can be titrated with NaOH (see also example below) to the desired pH (but NOT more than pH 7.3! MES is NOT recommended for buffering at pH 7.4) I wouldn't recommend "re-titrating" by the use of HCl.
from only one Web-source: e. g. 1000 ml 0.5 M MES stock solution:
- • Dissolve 97.6 g MES (free acid) in 800 mL of ddH2O
- proper pH-Measurement (use proper electrode settings!) , THEN
• Adjust the pH to the desired value with 10 N NaOH
• Bring up the volume to 1 L with ddH2O
[CAVE: OVERTITRATION by careless/ 'speeding' admixture of too much volume of highly concentrated 10NaOH, as mentioned in this recipe! / re-TITRATION would be necessary but then you'll end up with a - basically spoken - olla podidra/mishmash of 'ions'.
First of all I would search for the cause of your distilled water's HIGH pH, which - at least in my experience - is quite uncommon! (either you have a contaminant in your distilling device [which I can't believe in if it (even) is a regular distillator/water still or even if you use poor quality plastic containers for shorter periods of storage]
OR you have a contaminating component in your MES-powder
OR use A. demin. from an ion exchanging device the ion exchange resin is defect or out of function....
There exist a lot of tables and figs. about adjusting all kinds of buffer solution.
In your case, titrating an alkaline buffer solution (you created/fabricated from a buffer usually resulting in pH2.5 to pH5.0 only by the addition to your "A.dest") I doubt you might be successful in "re-titrating" with (dilute or concentrated HCl) because you change the concentration of the participating ions and/or the volume of your buffer solution significantly.
Since you utilized only approx. 20 g MES for your wrong solution I'd propose to discard, to find the cause for your high-pH-a.dest.source and then to start again, making a 0.5 M. solution (see above) which you can dilute as appropriate.
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