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Home Cosmetic Science Talk General Science Lactate Buffer at pH 6.0 for urea stability (referenced in study)

  • Lactate Buffer at pH 6.0 for urea stability (referenced in study)

    Posted by localhost on November 9, 2021 at 6:14 am

    I am trying to figure out how this study is creating their Lactate buffer at pH 6.0.:

    They reference making it on page 188:

    Lactate buffers pH 4.5 and 6.0, phosphate buffer pH 6.0, and citrate pH 6.0 were prepared according to European Pharmacopoeia (14)”

    I checked the European Pharmacopoeia edition they sourced and found no lactate buffers at all.

    Here is the full article:

    The pKa for lactic acid is 3.86.  How is it possible to make a buffer with it at pH 6.0?

    Can anyone clue me in here?


    localhost replied 1 year, 4 months ago 2 Members · 7 Replies
  • 7 Replies
  • localhost

    November 9, 2021 at 6:17 am

    If that link doesn’t work try this one, sorry:

  • Pharma

    November 9, 2021 at 8:53 am
    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…
  • localhost

    November 10, 2021 at 1:53 am

    Can you explain how they get this result:

    According to the optimum result in retarding urea decomposition in aqueous solution, preparations adjusting with lactate buffer pH 6.0 were subjected to study in this experiment. Pharmaceutical preparations composed of urea at varying concentrations of 2.5%, 5%, 10%, 15%, and 20% (w/w) with pH 4.50 (no further pH adjusting) and pH 6.00 (adjusting with lactate buffer) were examined. Table V demonstrates the values of the rate constant, 4, in h” calculated from the experimental data of the residual urea concentra- tion as a function of temperature. Within the experimental range of temperature and initial urea concentration values, the lowest urea degradation was found with lactate buffer pH 6.0.

    Is it just the sodium lactate in the pH 6.0 lactate buffer giving the least degradation?

  • Pharma

    November 10, 2021 at 12:40 pm
    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.
  • localhost

    November 10, 2021 at 1:37 pm

    I’m curious how a study published in the Journal of Cosmetic Science got something like that wrong.  If it makes no sense to someone like me, how did they not realize it?

    Would you mind taking a look at my formula telling me what you think?

    Purified Water to 100%
    Propylene Glycol 10.00%
    Glycerin 2.00%
    Xanthan 0.30%
    Xylitol 3.00%
    Petrolatum 10.00%
    Mineral Oil 8.00%
    Caprylic/Capric Triglycerides 3.00%
    Cetearyl Alcohol (and) Polysorbate 60 3.00%

    Urea 5.00%
    Sodium Lactate 2.50%
    Germaben II 0.50%

    Buffer (50mM at pH 6.0): 

    Citric Acid (anhydrous) 0.12%
    Sodium Citrate 1.28%
  • Pharma

    November 10, 2021 at 9:03 pm
    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).
  • localhost

    November 10, 2021 at 11:38 pm

    Good to know that about the journal.  

    I will take your advice.  Much appreciated.