Home Cosmetic Science Talk Formulating Citrate buffer preparation

• # Citrate buffer preparation

Posted by on December 10, 2022 at 9:56 pm

HI!
I am struggling to find a formula on how to prepare Citrate buffer pH 5.5 out of kitchen Citric acid (monohydrate) and Trisodium citrate dihydrate (I get it reacting citric acid with baking soda).

I am confused since one formula is provided by Ethyl ascorbic acid manufacturer. There is a suggestion to use 84% water, 1% citric acid and 15% sodium citrate to get a buffer pH 5.5.

Then there is a web-site to calculate the buffer: https://www.aatbio.com/resources/buffer-preparations-and-recipes/citrate-buffer-ph-3-to-6-2
Although there is a dehydrated citrcic acid used, I recalculated it to monohydrate using their g/mol values and got 6,235g citric acid and 20.684g sodium citrate, which is not 1% and 15% like above.

Then I also found this table https://www.sigmaaldrich.com/UA/en/technical-documents/protocol/protein-biology/protein-concentration-and-buffer-exchange/buffer-reference-center#citric2

They don’t have pH 5.5 buffer in the table, but for pH 5.4 it is 5,358g Citric acid and 21,910g sodium citrate. The relation is different again! I am confused

So my question is what is the formula for Citrate buffer with above ingredients to get pH 5.5. Also, is there any standard, or common, or widely used percentage of buffer which used by formulators?

replied 1 year, 2 months ago 2 Members · 2 Replies
• 2 Replies
• ### gordof

Member
December 19, 2022 at 1:48 pm

all of the mentioned are correct just the buffer amount of each of them is different.

There is not one percentage that forms a buffer system the combination of Citric acid and Trisodium citrate forms the buffer and depending on the Variation of the concentration the buffer system can Buffer for more or less on the given ph Value.  so if you have ingredients that constantly strangle your ph like Urea for example you need more buffer if you don’t have any and just want to ensure a Slim line for the Specification or an Activ will only work at 5.4-5.6 you use only a smaller amount of both.

• ### fareloz

Member
December 19, 2022 at 11:12 pm

But I would expect the same ratio of ingredients, e.g. 1 to 4 or something like that, but the ration is different…