Pharma
Forum Replies Created
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Salicylic acid carries one carboxylic acid group, citric acid has three. Under physiological conditions, citric acid is ‘twice as acidic’ than salicylic acid or, in other words, 1 M citric acid is 2 N whilst 1 M salicylic acid is 1 N.
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Salicylic is stronger by pKa but poorly soluble and has a lower ‘charge density’ (1 M salicylic acid gives less acid that 1 M citric acid).
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@mbach What exactly are you making? A dry shampoo for ‘dry washing’ or a dry base to be diluted with water and used as wet shampoo?
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The Journal of Cosmetic Science isn’t a good journal and only publishes incomplete, poorly designed & executed, and unreviewed stuff you can’t publish in a ‘real’ scientific journal. Publications therein are usually what I call crap.Finalise the buffer by adding citric acid in the end until you hit pH 6 and don’t just add what the calculation says
. Else, if it’s stable and feels nice… nothing to add (a chelate might not be necessary with the large amount of citric acid). -
@PhilGeis Fun? Claim? Too much free time? Finally a use for the pH meter? :smiley:
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No. lactic acid is weaker than citric… Best go with a strong mineral acid such as HCl
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Looked it up in the PhEur: There is no lactate buffer, let alone for pH 6.Also, using lactate buffers at that pH is against logic and not compliant with PhEur. PhEur lists a few phosphate buffers and a MES buffer for said pH.Anyway, urea is most stable at pH 6.2 (IIRC) and that is independent of how you get to that pH cause all that counts is the pH. Given that degradation of urea raises pH, a buffer or other means which keep pH from raising (such as triethyl citrate or triacetin) is the way to go.
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At pH 3 and in conjunction with citric acid, most is in salt form and most citric acid is in acid form. Nothing gained here.
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10% methanol should be fine. However, not every alcoholic solution can easily be measured
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It will fall out of solution cause salicylic acid isn’t really soluble in water
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Theoretically, you’re correct (I didn’t do the maths but I sounds about right).The ‘problem’ with larger quantities is:Add ‘active acid’ -> increase pH with strong base = part ‘active acid’ & part ‘active salt’Add ‘active salt’ -> lower pH with strong acid = part ‘active acid’ & part ‘active salt’ & part saltAdd ‘active salt’ -> lower pH with weak acid = part ‘active acid’ & part ‘active salt’ & part acid & part saltThis may not be an issue when the ‘active’ is a preservative at 0.2% but in case of 5% sodium lactate and citric acid the electrolyte load gets huge (sodium lactate plus sodium dihydrogen citrate) and you’ll also have ‘active’ citric acid, not just ‘active’ lactic acid.
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Lactate buffer at that pH doesn’t properly work, it’s 99% sodium lactate. It does prevent a drop in pH but that’s not going to help with urea.Never use the PhEur for buffer preparations…
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Yes, 1 unit below pKb means 90% protonation, 2 units 99%, 3 units 99.9% and so on.
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Preservatives are used in their salt form because of solubility. Were the acids water soluble, then using them as salts would be stupid. So many people take the salts, mix them in, and lower the pH with whatever to turn the preservatives into active acids. The amount used is also way smaller than 5%
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Pharmacopoeia for bentonite .Olivem should have melting point, saponification and other specs you could test.Olive extract: TLC or HPLC.The wax… meh…
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I recently tried something out and thought I’d incorporate 4 new ingredients. I had to ‘balance them out’ (using HLD estimations) with some more ingredients, added oils and butters to give a nice viscosity/spreading cascade, topped that with a mimicry of NMF (polyols, amino acids, HA, etc.), rounded it off with some actives I like, and had to preserve all with the ‘hurdle approach’ (bunch of stuff)… ended up with a LOI with 40+ positions. Well, easy, quickly measured whatcha worry, right? Yea, it looked fine for an hour and then phase inversed and now looks like slimy piss and has a funny fishy odour. Good job, I’m so proud of myself! I now can pretty much draw straws which of the different things caused the issue (I have a suspicion but to test that, I’d have to weigh anoter 40 times). :smiley:By weighing/wasting less ingredients I could have made 4 different products which would not just have been more stable but would also have given me a real impression on how those 4 new ingredients actually feel like…KISS is the way to go (I hate it and it somehow hurts… and hence I ignore it repeatedly just to proof to myself time and time again that life would be easy if you made it easy).
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Why don’t you just add lactic acid instead?See, if you use an acid to turn a salt into one, you end with a salt… Either combine lactic acid with sodium lactate or use ~5% lactic acid and set the pH to 3.5 using sodium hydroxide.
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I don’t know the pKb of the two… should be in the range of 5-6. Assuming it were 5, only 90% would be protonated at a pH of 4 whilst 99% would be protonated a pKb of 6. Number 3-5 are always at 100%.90% is good enough to feel and behave like a cationic emulsifier but it makes things a bit susceptible to pH shifts and ‘molecular’ interactions.
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Ghee is heated and dehydrated butter. The result is minor amounts of dissolved water in lots of fat. On one hand, that water is soaked up by fat through a process called swelling, the water molecules aren’t really free. And on the other hand, butter contains short to medium chain fatty acids which show some antimicrobial activity. Alsongside all the fat comes a bunch of water soluble stuff which reduces water activity within ghee even more. Likely, most microbes within the fat are cooked dead too. That’s why ghee stays fairly safe (until some fat eating microbe comes along). Cosmetic ghee would/should probably be preserved but more likely goes rancid faster than the bugs can grow.Imagine, water is one of the main contaminants in raw materials… sometimes it’s just a nuisance, sometimes your stash will putrefy.
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Depends .
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1 and 2 are weak because these are ternary amines. You have to add an acid to protonate them and turn them into positively charged molecules. The pH of most cosmetic products is not low enough to protonate 100% but only enough so they can act as ionic emulsifiers.The three others are strong because these are quaternary amines. They have a permanent and pH independent positive charge.
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If you took a strong acid such as hydrochloric or sulfuric acid: Yes, absolutely.Citric acid on the other hand is only slightly more acidic. You will be able to achieve a pH of 3.5 but that’s within the buffering ranges of lactic acid and two out of three carboxylic acid groups of citric acid. Such a blend will not perfom the same as a buffer of lactic acid plus sodium lactate. I don’t know if it’s stronger (a lot more total acids) or weaker (better buffering).
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Abdullah said:@Pharma Just to check that i have understood correctly, of i use ionic+fatty alcohol+ non-ionic surfactants at 5% total, should i use 5-10% of this 5% which is 0.25-0.5% ionic, 0.25-0.5% non-ionic and 4-4.5% fatty alcohol?
Correct. With weak ionic ones such as lactylates, better go with 0.5% whilst strong ionic ones such as SLS or SLES work well with the lower amount. It always depends a bit on what you have in your system, so this is just a rule of thumbs.
You could also use cellulose and starch derivatives or chitosan. Sadly, most aren’t as performing as the anionic polymers, they require higher inclusion rates and tend to feel slimy/tacky. Different cationic and non-ionic synthetic polymers (polyesters, polyamides, quaternized polymethacrylates, PLGA…) are used for example in pharma… I don’t know if any of these are available for cosmetics and/or perform good enough as cosmetic gelling agents. -
Typical hydrophobically modified polymers are found amongst the carbomers and polyacrylates such as Carbopol Ultrez 21. Another one would be ethyl cellulose (often not considered as ‘modified’ due to a too high degree of lipophilic linkers)… it’s not a typical one, behaves differently, and has different uses and perks.I admit that I love chitosan. However, I haven’t come across hydrophobically modified one… and now I have to Google that :smiley: .
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About 0.4% (a typical partner for your combo would be sodium stearyl lactylate). Sodium stearyl lactylate as well as stearamidopropyl dimethylamine may, due to their pH sentitive ionicity, be added at even higher % depending on pH. The former gets less anionic at low pH, the latter less cationic at higher pH. I never work with stearamidopropyl dimethylamine but I would really give it a try. I like cationics and think they feel really nice (I played with Emulsense and Varisoft EQ 65 combined with polyglyceryl esters and they play reall real nice together)! One drawback is that you can’t use anionic polymers for thickening…Regarding you second Q: No, I mean high HLB. Traditionally Tween 20 but for ingredients from renewable resources, polyglyceryl-10 laurate would make a suitable substitute (start in the range of 5% with regard to total emulsifiers and go from there).