Welcome to the first Dispatch. The idea here is simple: one short letter, every Saturday, on the things that actually move the needle when you're comparing research peptides — and nothing that doesn't. Let's start with the document everyone waves around and few people read closely: the certificate of analysis.
What a COA is, and isn't
A COA is a lab's statement about a specific batch. It is not a guarantee about the vial in your hand unless the batch numbers match. The single most useful habit you can build is checking that the batch on the COA matches the batch on the vial. Most people never do.
"Purity ≥99%" — read the method
Purity claims mean very little without the method behind them. HPLC purity and mass-spec identity answer different questions. A vendor quoting "≥99%" without saying what was measured is telling you a number, not a fact.
The number on a COA is only as good as the sentence describing how it was measured.
How vendors talk past each other
Read three vendor COAs for the same compound and you'll often find three different things being reported as if they were the same thing — purity, identity, and content used interchangeably. They aren't. When you compare vendors, compare the same measurement, or you're comparing nothing.
That's the whole letter. Next week: why the biggest vial is often the worst per-mg deal. See you Saturday.