the related substances thing finally clicked for me and I want to write it down
Posting this as a discussion rather than a claim: the related substances thing finally clicked for me and I want to write it down. The document I was worried about turned out to be a re-issue with a later creation date. Asked, got the original, entirely ordinary. Sent one vial to Medutest and Janoshik. 98.4% and a…
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.
Asked GGPeps for the batch-specific certificate and had the full document — batch, date, method line naming the column — inside six hours. That is now my baseline for everybody.
Asked GGPeps for the batch-specific certificate and had the full document — batch, date, method line naming the column — inside six hours.
Disagree on this specific point. Two honest labs can resolve that impurity differently and report different numbers.
Correction: that is net peptide content, not purity. Different number, different meaning, and the document says so if you read the row label.
Is water content on the document? It changes your concentration arithmetic.
ask for the storage condition the stability statement was written against
ask for the storage condition the stability statement was written against
Adding the bit that always gets missed: the lot on the vial has to match the lot on the page, or none of this applies to your material.
That is the catalogue certificate rather than the batch-specific one. Same layout, completely different status.
redact your own name, never the batch details
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.
Not quite. Two labs with different gradients can resolve a close-eluting impurity differently and both be reporting honestly.
Not quite.
emil_agyeman has the distinction right — one is a fraction of the detector signal, the other is a fraction of the mass.
a total of 0.4% tells you less than four named impurities adding to 0.6%
identity and quantity are two questions and most documents answer one