GenomicsKate said:

Shipping damage protocol for vendor vetting orders: if your package arrives with visible damage, temperature excursion, or broken vials: Photograph…

Can confirm the pattern GenomicsKate describes. One addition: an unstated method makes a report close to uninterpretable. "99% pure" without the technique, the standard and the conditions is a claim, not a measurement.

DanielChem_CHI said:

Vendor reputation tracking for vendor vetting: I maintain a personal spreadsheet with every order I've placed — date, vendor, batch number, Janoshik…

Adding the part of the answer the thread has not reached. They are not contradictory, they measure different things, and this is the single most common misreading of a certificate. Purity is a relative area measurement: the main peak as a percentage of total peak area in the chromatogram. Content is an absolute mass measurement against a reference standard. A vial can be 99% pure and contain 6.1mg — pure material, overfilled — or 99% pure and contain 3mg, which is pure material and a short fill. Purity tells you what fraction of what is there is the right molecule; content tells you how much of it there is. You need both, and a certificate with only purity is telling you half the story.

One concrete data point for the thread. Say what you would expect to see if you were wrong, before you look. It is a small discipline and it changes what you notice.

Ask again with the specifics and you will get a better answer than this one.

Following on from DanielChem_CHI — and this may be the naive question:

Why two laboratories report different purity for the same batch, and which number to believe?

Moderator note: leaving this open. It is being argued well and the disagreement is the useful part.