I used glycine in a hydrogel network structure. From a bunch of hydrogels the ones that contain Glycine turn into pink/reddish color when they are kept in pH 14 solution for a couple of days.
How can I explain it? Is there a side product or a reaction that gives an explanation to that?
Not sure but this might be due to the formation of copper salts of the aminoacids (glycine) in the strong alkaline solution, of course if there is any copper in the medium
There was no Copper medium.
But the stirrers were used during some Cu adsorption tests and then cleaned. I don't know if it might have an effect on that. Maybe I should just duplicate the experiment by doing it again.
My first approach would be to test whether it is reversible, by changing the pH. You said it is after a couple of days, so it is a thermodynamically driven reaction. So the reverse reaction might take a while as well.
Do MS measurements with freshly prepared hydrogel at pH 14 and the reddish one.
Do you have any other metals in there even small quantities can result in color changes? Small amounts can come from acids bases solvents and the glycine itself.
For example, some NaOH contains mercury due to the industrial process used. Mn ions for instance sometimes have a pinkish color. Iron impurities can give you brown iron hydroxy and oxides.
To test for trace metal contaminants, ICP MS would be suitable.
It is not reversible. I washed the hydrogel with Milli-q water several times and placed it into NaOH solution as well. The pink color was not observed again. The complex wwhich causes the pink color might be washed away.
I'll try MS measurement.
I have used brand new vials, stirrers etc. to make sure that no impurities comes within the materials resulting from previous experiments but the color change is observed always. I use smart spatulas (they are disposable) to prevent any impurity involved from the main materials.
I'll look for the possibility of ICP MS usage in the institute.
Thank you for your answer.
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