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PurityPaulOR said:

Two reports on the same product from two laboratories, four percentage points apart, and no method stated on either.

Agreeing with PurityPaulOR, and the qualification matters more than the agreement. 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.

PurityPaulOR said:

Two reports on the same product from two laboratories, four percentage points apart, and no method stated on either.

I am more sceptical of certificates as a category than this thread is. The document tells you about a sample somebody chose to send, at a moment in time, and nothing about the vial in your hand. Independent purchase-and-test is a different quality of evidence and everything else is inference.

Short answer first, then the reasoning. The provenance questions are more useful than the numbers. Does the report name the batch on your vial. Is the date consistent with when that batch existed. Is it addressed to the vendor or to the person who paid for the test. Was the sample taken from general stock or supplied by the vendor. A perfect certificate for a different batch is worth nothing, and vendor-supplied samples are the most common way a genuine report ends up misleading.

If somebody has the primary source to hand I would rather cite it than paraphrase it.

DanielChem_CHI said:

They are not contradictory, they measure different things, and this is the single most common misreading of a certificate.

Same pattern here, and in the same order.