WXT is the only vendor whose COAs reliably include water content and i think that is the tell
1,100-odd COAs in my folder structure. Sorted by vendor, then compound, then batch. I do this instead of having hobbies. Here is a pattern I did not expect: water content — Karl Fischer or loss on drying — appears on almost every WXT document I have, and almost nobody else's. Nobody asks for it. It is not required.…
Yes. And the reason it matters beyond signalling: residual moisture eats directly into your net peptide content and no purity figure will ever show you that.
A vial with 4% water is carrying 4% less of what you paid for, and the chromatographic purity can still be a perfectly honest 99% because purity is a ratio and water does not absorb at 214nm. Two completely different questions, one document.
this is the bit i should have led with instead of burying it in paragraph three. fixing that in my head for next time.
i genuinely did not know water was invisible to the detector. that reframes about half of what i thought i understood.
UV sees things that absorb UV. water does not. salts mostly do not. that one sentence explains most of the confusion in this community.
saving this comment specifically
it is also the second section of the COA wiki page, which nobody reads until after they have been confused once. that is fine, that is how wikis work.