6 replies·
Got shown a certificate of analysis. It has a chromatogram, a percentage, and a lot of numbers. I have read the post on testing and I follow the argument but I still could not tell you if a given certificate is any good.
What is the actual checklist?
The checklist is shorter than you would expect, because most certificates fail at step one.
1. Two techniques, or one? HPLC and mass spec answer different questions. HPLC says "how much of this sample is one substance" — purity. MS says "and that substance is the one on the label" — identity. A certificate with only HPLC is telling you the vial contains 99% of something.
2. Whose name is on it? In-house means the seller tested themselves. Not worthless, but it is a self-assessment. An independent lab's letterhead is a different document.
3. Does it identify this batch? A batch or lot number that matches the vial in your hand. A certificate with no batch number, or one that does not match, is a certificate for a different substance.
4. Is it a picture of a document? A PDF that is a photograph of a printout has been through a step where anything could have happened.
5. Date. A certificate from two years ago describes a batch from two years ago.
Fail one, treat it as decoration.
The one I would add: what the percentage is a percentage of.
99% purity by HPLC at a given wavelength means 99% of what absorbed at that wavelength. Things that do not absorb there are not in the denominator. Salt, residual solvent, water content — none of that necessarily shows up.
It is not that the number is a lie. It is that it is answering a narrower question than "is this vial 99% peptide", and it gets quoted as though it answered the wide one.
Correct, and the honest version of that is that peptide content by amino acid analysis is the number you would actually want and almost nobody reports it. HPLC area percent is what is cheap.
Worth stating the obvious conclusion of all this, which the post is more polite about than I will be: a certificate is a document, and documents are the easiest thing in the entire supply chain to produce.
Nothing about a PDF is evidence of what is in a vial. It is evidence that somebody was willing to send you a PDF.
Ran the checklist over the one I was sent. HPLC only, in-house, no batch number, and it is a photo of a printout.
So — decoration. That was quicker than I expected.
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