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Ethanolamine-HCl solution storage

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Anyone knows the recommended conditions for storage of ethanolamine-hcl solution. I need to use it in an SPR experiment to inactivate the remaining NHS-esters after EDC/NHS coupling step.
However, I have observed that ethanolamine-hcl may not be working properly. It does not cause any (net) RU shift. I suspect I am not handling the solution properly. Plus my analytes are binding to control channels. Dissociation is virtually impossible for both test and control channels indicating proteins (analytes) are binding to the unreacted activated COOH groups on the sensor surface
How do I store the solution? Refrigerated? Frozen? or need to wrap parafilm around falcon/bottle cap? protection from light? what am I doing wrong?
So far what I know is that in solid form its hygroscopic, the solution shouldn't be. I saw one paper recommended make solution and then store in aliquots on -20. Light sensitivity not reported.
I make solution in a 50mL falcon, adjust ph with NaOH (8.5) and store at 4, no wrapping no light protection

It should be stable if it is a tight stopper on the flask, just glass is fine.

Can you explain the term "RU shift?"

Since this is for an SPR experiment, RU stands for resonance unit. 1RU shift is equal to a critical angle shift of 10-4 deg

As long as the pH is adjusted correctly, I cannot see a problem.  BTW, there is some literature on following NHS coupling reactions: DOI: 10.1039/c5ay00042d.  My situation was a little different; I tried to use spectrophotometry, based on the absorbance of the side-product (which as a pKa of 6) with mixed success.


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