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Strength of HCl to order for pH adjustment
I’m looking at ordering some HCl for pH adjustment. I don’t want to order a concentration so high that I’ll need a fume hood to work with it safely. Just safety goggles, chem gloves, long sleeves. Would a 10% HCl solution be strong enough to adjust pH for typical cosmetic formulations? Or should I order a 25% solution? I can dilute down and create lower molarity stock solutions easily enough, but don’t want to order HCl too weak to be generally useful or too strong to be an inconvenience or (respiratory) danger.
A 10% HCl solution is 100mg/mL HCl, or approximately 3.33mg/”drop” HCl (varies…). A log calculation shows that only 3.65 mg HCl is needed to reduce pH of 1 liter of pure water to 4.0.
I’m guessing that an order of magnitude more (~36.5 mg/L?) may compensate for 0.35% sodium benzoate, for example. That’s still feasible with 10% HCl while trivially altering the volume.
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16 Replies
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Why not use Citric acid? More commonly used and less dangerous.Read some representative Cosmetic Formulations and you will almost never see HCl used but almost always Citric Acid. -
Microformulation said:Why not use Citric acid? More commonly used and less dangerous.Read some representative Cosmetic Formulations and you will almost never see HCl used but almost always Citric Acid.- HCl is the most efficient acid for pH adjustment and I would like to have HCl and NaOH readily available for their own sake. I like efficiency.
- I suspect some are sensitive to citrate in the range ≥0.2% and want the option of eliminating it without substituting a more irritating molecule, like lactate.
- I’m working within a tight osmolarity range, and hope that using HCl will give me more room for my humectant while reducing the buffering capacity of my formulation.
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In many, many, many years of personal care in R&D and manufacturing, I can’t recall HCl EVER being used in a Commercial setting for Personal care.The Lab Safety issues, the Hazardous Material issues and Marketing perceptions attached makes the use of HCL naive and ill informed.
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@Mayday I doubt that either citrate or lactate at the concentrations you have mentioned above can cause any sensitivity simply because they are a significant part of multiple bichemical reactions in a human body.
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Microformulation said:In many, many, many years of personal care in R&D and manufacturing, I can’t recall HCl EVER being used in a Commercial setting for Personal care.The Lab Safety issues, the Hazardous Material issues and Marketing perceptions attached makes the use of HCL naive and ill informed.If I were in your position, I am sure I would feel
the same way about another person asking this question—I would have to assume
they would hurt themself or somebody else.I appreciate the warning, and I admit I am naive, but I am not wholly ignorant of those aspects. The consumer perception by itself is likely enough to make it a nonstarter. However, I am not seeing a technical reason to avoid HCl. (Some previous discussion linking to industry usage.) At the moment, I’m formulating for strictly personal use and am prepared to give HCl proper respect as a chemical, diluting as needed and double checking pH.There are plenty of substances that can cause chemical burns and respiratory problems if mishandled. I think avoiding all of them is not practical. Lactic acid 90% has to be handled carefully, and plenty of powdered ingredients are respiratory irritants. Sodium hydroxide is caustic. It is because I am concerned about safety that I am asking about 10% and 25% HCl, rather than running out and buying the strongest concentration I can find in a misguided attempt to “save money”.vitalys said:@Mayday I doubt that either citrate or lactate at the concentrations you have mentioned above can cause any sensitivity simply because they are a significant part of multiple bichemical reactions in a human body.Metabolic citrate or lactate is one thing, citrate or lactate applied to skin or mucosa is another thing. That’s a little like saying HCl must be safe because it’s in gastric acid (~0.5% HCl). I wouldn’t want that on my skin. The concentrations and context matter.
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Have you ever worked in a Manufacturing Setting? They would give you push back. Listen to people in the know, know what you don’t know and use Citric acid as it is more of an Industry standard. Using HCl is mind boggling and dangerously naive/Wisdom is knowing what you don’t know.
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Lactic acid and citric acid is in the body of every person. No one is sensitive to these. If you are concerned about exfoliation ans sun sensitivity then be sure that <1% lactic acid will not exfoliate anything.
If you want to use HCl knowing the risks use 1% solution.
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@Microformulation I really appreciate your advice, but I wish you would elaborate more on why it’s a bad idea. Let me try to make your case, because I think I understand where you’re coming from.
- HCl in a manufacturing setting would be sourcing the highest concentration practical to work with (perhaps 37%) for cost reasons. A mistake in formulation could easily create a solution that is corrosive and extremely dangerous. If you don’t have rigorous SOP and quality control, you could hurt somebody: destroying your brand and opening yourself up to litigation and/or criminal prosecution.
- Because of the severity of a negative outcome, you would invite more regulatory scrutiny.
- Consumer perception of HCl as an ingredient would invite civil litigation and poison your brand in the case of adverse reactions, even if entirely unrelated to your product. More so if your product has very few ingredients and the HCl is not buried at the end of a long list.
- For all the above reasons, contract manufacturers will not want to manufacture your product, because they would share in the liability.
None of these are technical reasons to avoid HCl, but they are practical reasons to avoid HCl.I’d appreciate it if anyone else can chime in on this topic, in case I’m missing something important. -
@Abdullah Thanks for the link to prior discussion. Looks like buying 10% and diluting to 1% stock would be acceptable.
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@Mayday According to your conclusions regarding using HCL, you may also give it a try to HNO3 or let’s say H2SO4… Could you explain why HCL?
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@Mayday What do you mean by saying this: “I’m working within a tight osmolarity range, and hope that using HCl will give me more room for my humectant while reducing the buffering capacity of my formulation…”
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vitalys said:@Mayday According to your conclusions regarding using HCL, you may also give it a try to HNO3 or let’s say H2SO4… Could you explain why HCL?See this comment by Perry.pH is related to the concentration of H+ (aqueous) ions in solution. They are actually H30+ ions (hydronium ions) because the hydrogen from the solute is too unstable alone. Free Cl- (aq) ions will be equivalent to the Cl- (aq) ions from NaCl dissolved in water if you have any salt in your formula. So HCl will have no “side effects” besides the extra electrolyte. The “purity” of HCl is why it is used extensively for pH adjustment in labs.I haven’t studied the chemistry of nitric or sulfuric acid. SO4 (sulfate) is apparently used as an osmotic laxative, but I imagine it would smell/taste awful and rotten. NO3 (nitrate) is a component of sodium nitrate, which is used for meat preservation. With enough dilution, neither HNO3 or H2SO4 should oxidize human tissue (chemical burn), but I think they would be unsuitable for reasons. For one, because some idiot will use recycled battery acid rather than FCC or better grade H2SO4 and give somebody lead poisoning or something.
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vitalys said:@Mayday What do you mean by saying this: “I’m working within a tight osmolarity range, and hope that using HCl will give me more room for my humectant while reducing the buffering capacity of my formulation…”Most solutions do not need to be iso-osmolar with human blood (~300 mOsm/L). Some should be, such as water-based personal lubricant. Other products could benefit from being iso-osmolar, such as a gentle face wash.My guess is that a face wash formulated to be iso-osmolar, with ingredients at concentrations known to not cause ocular irritation, the absolute minimum buffering capacity (by formulating to minimize pH adjustment), would be non-stinging to eyes even with direct application. Obviously, formulating eye drops is outside the realm of cosmetics, but there are principles that can be applied to cosmetic formulations.
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in case I’m missing something important.
I am sorry, @Mayday indeed, you are missing something important…
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