Much is made of trying to find the optimal storage conditions for nicotine concentrates to be diluted into working eliquids. Similarly, much is also made of finding concentrates with good pure nicotine.
These are good things, but ultimately, I wonder how much they really matter.
Consider this image from Exogenesis. This is from his vapor trapping experiments where he set up an apparatus to auto-vape e-liquid and electrostatically condense the vapor for nicotine determination:
On the left, you see eliquid made from pharma grade nicotine. On the right you see the same liquid after it's been atomized and condensed.
No matter how well we source and store the stuff, the stuff on right is what we're vaping, not the stuff on the left. After all, the last thing we do before we inhale our precious liquid is heat it up aggressively in a stream of air containing about 20% oxygen.
I'm not out to make a big deal about this inescapable fact of vaping, but it's at least something to consider when we might be tempted to worry excessively about our concentrates getting a slight yellow/brown tinge.