[Lab] FGP BPC — PeptideMeter came back 99.6% against a claimed 99.0%
Short version of the title, which is already short: FGP BPC — PeptideMeter came back 99.6% against a claimed 99.0%. Longer version underneath.
Since the title puts numbers in the shop window: 99.6% and 99.0%.
Ask what the stability statement was written against — temperature, light, and whether it was the lyophilised powder or the reconstituted solution. Those are three different claims.
LC-MS gives you identity; UV purity gives you a relative quantity. A document with the first and not the second, or the reverse, is answering half the question.
Not medical advice, obviously, and nothing here is approved for human use. One person with a spreadsheet.
- FGFGP source pageFlourishglobal Peptide Biotech (Chengdu) Co., Ltd. · Chengdu · 89% here, rank 20 · shop at flourishglobalpeptide.net →
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UV at 214nm sees the peptide bond and picks up almost everything; at 280nm you are looking at aromatics only. Which wavelength the number came from is part of the number.
Small fix — 214nm, not 280nm. It matters here because the impurity you are asking about barely absorbs at the longer wavelength.
Yes — and the reason to ask for the whole page is that the interesting parts are the ones people crop out to fit a screenshot.
Pushing back a little: a missing field is usually presentation, not concealment. Ask for the full document before drawing conclusions.
Why the same vial can honestly produce three different numbers.
Purity by area percent is relative to what the detector saw on one gradient at one wavelength. Net peptide content subtracts counterion, water and residual solvent. Mass of peptide per vial is net content times fill weight, and fill weight has its own tolerance.
So a document reading 99% purity, 6% acetate and 4% water is describing a vial that is about 90% peptide by mass, and every one of those numbers is honest. The mistake is treating the headline figure as the answer to "how much peptide did I get".
Related substances itemised individually is a much stronger document than a single total, because it tells you the shape of the impurity profile rather than its size.