Oxidation rate/testing of 15% ascorbic acid at pH of 2.85

I make a simple 15% L-ascorbic acid water for myself. I use 1% sodium lactate to increase the pH to 2.85. I've been tinkering with the formula, so I've been making a new one every few days and keeping the old ones in a drawer for occasional observation. No changes in the color have happened yet. The first few experiments I used 0.5% of Liquid Germall Plus (Propylene Glycol (and) Diazolidinyl Urea (and) Iodopropynyl Butylcarbamate) as a preservative, but then I realized that the formula has a pH of 2.85 and LGP has a minimum pH requirement of 3.0. Originally, I was going to ask for a water soluble preservative recommendation for such an acidic formula (everything I've found thus far has a minimum require of 3.0), however, it's just occurred to me that I don't know if the formula is even stable enough to merit a preservative. I've searched for information on the oxidation rate of ascorbic acid, and I haven't found anything that gives me a ballpark in terms of time. Perhaps I'm not using the correct search terms.

Can someone point me in the right direction for a reliable source on the topic of ascorbic acid stability? Though a quick answer about the shelf life is helpful for the moment, I'd like to learn more about what actually happens. I've read something about H+ ions breaking free faster in highly acidic solutions, but not having a formal background in chemistry makes it difficult for me to immediately grasp exactly what's happening, so I figured I would keep reading until I understand the oxidation process. 

Also, if the formula would be stable for more than a few days, a preservative recommendation would be appreciated, as I would like to avoid growing things in my experiments.

Side note, yes I'm aware of using ferulic acid and vitamin e to stabilize ascorbic acid; however, I'd like to first learn what happens in a simple formula before expanding into more complex variations.

Last question, is there a way for me to test the oxidation of the ascorbic acid solution at home, i.e. something akin to a pH meter?

Thank you.


  • MarkBroussardMarkBroussard Member, Professional Chemist
    Sounds like you need an Ascorbic Acid Oxidometer.
    Chemist/Microbiologist formulating in the Organic & Naturals arena under ECOCert/Natural Products Assn/Whole Foods/National Organic Program guidelines focused skincare & haircare products. 

    See website for details www.desertinbloomcosmeticslab.com
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