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Author: Subject: ascorbic acid solution discoloration
agent_entropy
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[*] posted on 8-2-2018 at 09:41
ascorbic acid solution discoloration


I notice that when I make a fairly concentrated solution of ascorbic acid (as a handy aqueous reductant) after a few weeks it turns yellow and then dark orange-brown. This is no doubt the result of oxidation by atmospheric oxygen and/or degradation by light. My question is, how might one prevent such discoloration (besides the obvious storage in the dark)? And if possible, how might one prevent such discoloration in a food-safe manner?

Edit: The solution discolors even if kept tightly sealed in HDPE containers.

[Edited on 8-2-2018 by agent_entropy]
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Sulaiman
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[*] posted on 8-2-2018 at 09:58


and the solid powder also turns orange-brown within months of being stored away from direct daylight, but in a not quite airtight PE tub, so air/moisture could/would have got in.



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AJKOER
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[*] posted on 8-2-2018 at 17:00


I am not sure if it is even possible, but you must prepare your solution of dissolved Ascorbic acid carefully avoiding even the tiniest transition metal contamination (like from iron, copper, manganese, super trace amounts of cobalt,...). Also, boil the water to remove any dissolved oxygen. The Ascorbic acid in the presence of O2 and the transition metals can engage in a cyclic redox reactions with light an added catalyst. The product includes the hydroxyl radical which will attack ANY organic matter including the plastic bottle, ....

See my comments at http://www.sciencemadness.org/talk/viewthread.php?tid=77977#... .

Also, note the reference: "Generation of Hydroxyl Radicals from Dissolved Transition Metals in Surrogate Lung Fluid Solutions" by Edgar Vidrio, et al at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2626252/ , where apparently, transition metal content of dust particles (collected in the lung) is the 'contaminant' leading in time possibly to DNA damage, disease,..

[Edited on 9-2-2018 by AJKOER]
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