@Snake-Pepskin
Fair point, and appreciated โ I hadn't considered acetic acid for kisspeptin. Good to know for next time.
Here's why I still lean toward the vial rather than the recon, though: roughly 1/8 of the cake was fused to the glass wall. The other 7/8 dissolved without any trouble. If this were the compound being difficult at my concentration, I'd expect the whole cake to fight me, not for most of it to go in clean and one welded piece to hold out. The floating flakes look like residue from where it was bonded to the glass โ translucent, and the two bigger ones drift around like ghosts when you shake it up. Which is admittedly kind of cool.
Diluent was Hospira BAC, day 5 from cracking the seal. Used the same bottle successfully before and after this vial, so I don't think that's the variable either.
My read is that it happened at lyophilization โ a cake that partly collapsed or fused to the wall during freeze drying. Storage on the vendor's end is possible too; I'm taking it on trust that it was held properly.
Either way, they refused a replacement, so I won't be ordering from them again.