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Sodium citrate buffer
Hello. I’ve created a buffer solution with sodium citrate, citric acid and sodium hydroxide. My buffer pH is 5.4. I want to include it in a clarifying shampoo that should have a final pH of about 5.3-5.4. I found a site that does the calculations for you, so I used:
Aqua— 100ml
Sodium citrate— 4.813g
Citric acid— 1.659g
Sodium hydroxide—Qs to pH, 0.36g
Citric acid —0.16g because my ph was then a bit too high so I added a bit more
Aqua— Qs to total 250ml
But now what I want to know is when do I add the buffer? Do I do it at the end after I’ve adjusted the final pH or some time before? Note, I do hydrate cationic guar at the end (5.0-5.5), as well as do some heating to 70*C. Please lmk what you can suggest. TIA
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5 Replies
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Also, how much should I use in percentage or grams? I see some things that say as low as 0.1% to 5% and that’s a very wide range.
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I seek the same unswer,o more logically,it will be added at the end of formulation, im just guessing,but my question how to konw how much ,in un example i found after i have done my calculation that i sould add almoust 7 % of buffer solution , i found this too much ??
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Why are you adding it to the shampoo? What active is in the product that you’re trying to prevent a pH drift?
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Citric acid can be anhydrous or a monohydrate, and sodium citrate can be anhydrous, monobasic, dibasic, tribasic, all with different molecular weights that will affect your pH calculations. If you’re using anhydrous citric acid and tribasic sodium citrate, then you should be right at pH 5.35. Fyi, I use the Curtipot spreadsheet to get an accurate estimate of pH.
I’ve read that conditioners can have up to 5 w/w% citrate while shampoos are typically around 0.1-0.5 w/w%. So you seem to be pretty high at 2.6% for a shampoo. I don’t make shampoos though, so I’ll defer to someone else on whether or not this is appropriate for your formula. You’re also at a buffer concentration of 100 mM, which seems pretty high (though this depends on what you’re adding). Do you need that much buffering capacity in your shampoo, and does citrate serve any other purpose?
In my serums, I have to worry about hydrolysis (in my case, of esters), which is a pH sensitive reaction that is accelerated at higher temperatures. If your formula is acidic or basic at your 70C step (basic is normally worse), then hydrolysis might be a problem especially when heating for longer times. In that case, adding a buffer before that step might actually be helpful. At the same time, citrate is a chelator, and if you have metals in your formula you might have a higher chance to get color changes if you have it in there at 70C. Generally, I think the buffer is added at the end, but again I’ll defer to someone who makes shampoos since I only make facial serums.
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Thank you all for your replies. However, I’ve since figured out the formula and I have answered my own questions. I made various changes including less of each as well as how/when I add it to my formula. Thanks again
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