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Stabilizing urea with gluconolactone
Hi guys!
I read about stabilizing urea with gluconolactone. It was recommended to use it at a rate of 15% of urea. If I use 3% urea and try 0.45% gluconolactone it is much too acidic. If I reduce the amount of gluconolactone to bring it to around pH 5, the pH climbs at 45C stability test.
I haven’t yet tried to use 0.45% gluconolactone and then neutralizing it to an acceptable pH with NaOH yet. Would that make any sense?
Thanks!
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5 Replies
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You might try monitoring it for a couple of weeks or so. Gluconolactone tends to cause an acidic pH drift over time.
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Gluconolactone hydrolyzes/breaks down spontaneously in solution to gluconic acid. Consider https://pubmed.ncbi.nlm.nih.gov/25043489/
Are you determining urea levels in stability testing?
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What Phil & Mark said…plus there are simpler ways to stabilize urea. Most common is to employ a lactate/lactic acid buffer at pH5.5 or so. An uncommon one is to add rice starch to the formula. Some amyloid starches adsorb urea in solution retarding degradation into biuret and ammonia. Cool, huh!
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That’s very interesting. I tried to locate a study or other info to help me with using lactate and rice starch to stabilize urea, but no success so far. Do you know of any related studies or references?
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The original tale about lactate buffer started (I assume) with this paper: https://pubmed.ncbi.nlm.nih.gov/25043489/
But the problem is that Urea is most stable at pH 6.0 and decomposes to ammonia, which is basic. So you need an acidic counterpart to neutralize it. Lactic acid has pKa of 3.8. At pH 5.5-6.0 there is almost none Lactic acid in the buffer to neutralize ammonia in case of pH drift.
The paper is also criticized and its issue is described in this discussion on this forum: https://chemistscorner.com/cosmeticsciencetalk/discussion/urea/
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