I have found an online protocol on how to make the buffer, but I am not sure about the calculations. Could anyone give me a procedure?
Hi there,
The easiest (ie very few calculations) is to prepare 1M KH2PO4 (acid form) and 1M K2HPO4 (basic form) solutions and take a defined volume of either of the two and adjust pH with the other solution. As the wanted pH is roughly 1 pH unit beyond the second pKa of phosphoric acid then you would need 10 times more of K2HPO4 than KH2PO4. So by mixing 100mL of the former with 10mL of the latter you shouldn't be too far from 7.8...
Hi there,
The easiest (ie very few calculations) is to prepare 1M KH2PO4 (acid form) and 1M K2HPO4 (basic form) solutions and take a defined volume of either of the two and adjust pH with the other solution. As the wanted pH is roughly 1 pH unit beyond the second pKa of phosphoric acid then you would need 10 times more of K2HPO4 than KH2PO4. So by mixing 100mL of the former with 10mL of the latter you shouldn't be too far from 7.8...
Dear Sir. Concerning your issue about how can you prepare a 1M potassium phosphate buffer with a pH of 7,8 .Make up the following solutions :
(1) 0.2M KH2PO4 (g/ l)
(2) 0.2M NaOH
Add the vol. of 0.2M NaOH in table to 50 mls of 0.2M KH2PO4
and dilute to 200 mls.
pH 7.0 ,Vol. of NaOH is 29.63 mls
pH 8.0 Vol. of NaOH is 46.80 mls
I think the following below links and the attached file may help you in your preparation:
http://delloyd.50megs.com/moreinfo/buffers2.html#phosphate
http://www.immunologie-labor.com/cellmarker_files/IET_reagents_02.pdf
Thanks
Dear Dominique,
I found this in Researchgate with the calculations and different examples. Hopefully it is not the one you already saw and maybe it helps you,
https://www.researchgate.net/file.PostFileLoader.html?id=54f9c88fd11b8b402a8b4586&assetKey=AS%3A273725033779218%401442272541972
Regards
Make certain you know how hydrated your monobasic and dibasic phosphate is, and adjust your molar masses accordingly. Otherwise, you will think you are adding moles of the appropriate phosphate when you are really just adding water. This will skew your pH. In general your total moles of phosphate are Concentration x Volume (obviously), but you divide it between the monobasic (acid) and dibasic (base) forms as follows: moles acid = moles phosphate / (1 + 10^(pH-pKa)) moles base = moles phosphate - moles acid To get the exact mass of each, multiply the moles of the acid by the molar mass of the monobasic potassium phosphate hydrate, and multiply the moles of the base by the molar mass of the dibasic potassium phosphate hydrate. This method will work even if you decide you want a pH other than pH 7.8, within the buffering range of phosphate. Good luck with your work!
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