For example, are you distinguishing a test that confirms “this is compound X” from one that measures how much of X is present? I’d like you to expand on what you think identity testing can establish—and, just as importantly, what it can’t.
a sample can be nearly chemically pure and still fail an identity test—the contaminants may be absent, but the molecule itself could be the wrong sequence or a closely related analog. purity answers “what else is present?”; identity asks “what is this?”
Purity only tells you what was detected in the sample; it doesn’t establish whether the material matches the claimed identity. Identity testing needs a method that can distinguish the target compound from closely related impurities.
Exactly—“99% pure” and “this is actually the compound claimed” are apparently two different questions, because lab labels enjoy making simple things complicated.
A 99% purity number can still describe 99% of the wrong compound. Identity needs an orthogonal method—ideally sequence-level confirmation, not just a matching mass peak. Mass spectrometry alone can’t reliably distinguish some isomers or related analogues. Purity is a percentage; identity is a claim about what the material actually is.
Those are two completely different claims, and people keep treating a chromatogram like a name tag. Purity can tell you how much of the sample looks like the target; identity testing asks whether the target is actually what they claim it is.
Purity assays measure the proportion of detected material, while identity testing asks whether the material is actually the intended compound—two different analytical questions that shouldn’t be conflated.
…and a COA can look impressively precise while still not answering the basic “is this actually the labeled compound?” question. People treating one number like it settles the whole assay is kind of adorable.
The distinction between purity and identity testing stands out—something can be “pure” and still be the wrong compound, which is a spectacularly avoidable lab plot twist.
A sample can pass an identity test and still contain significant impurities, since identity usually confirms what’s present rather than measuring everything else in the sample.
Assuming a high purity percentage tells you what the substance actually is is doing a lot of heavy lifting. Purity and identity answer different questions.
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