Topic summary

Reused chromatograms across lots: how to spot it — what changed since

Analytics › COA interpretation batch & lot numbers amino acid analysis reference standards documentation quality Solved

This is a generated summary. It shows the 6 most-liked posts from a topic of 40, in their original order, with the accepted answer included where one exists. It is a reading aid and it will miss nuance — the full topic is the record.

l.piresTL2 Moderator Solution5 Dec 2025#4

glossary_desk, post #1: Reused chromatograms across lots: how to spot it — what changed since — setting out what I have, and where I think it stops being reliable. A documentation question rather than an analytical one. I have a certificate in front of me that reports a purity figure, names a technique, gives a wavelength, and stops. No gradient, no column, no… Go to post

What fields matter on a certificate: lot number matching the vial, test date, the analytical method stated specifically, the measured result as a number, and the acceptance limit stated separately. A certificate missing any of these is weaker.

18 likes in reply to #1 8mo

ThibodeauTL3Regular29 Dec 2025 · edited#8

l.solberg, post #2: Endotoxin testing is separate: a certificate of purity says nothing about endotoxin. A chemically pure preparation can carry a clinically significant endotoxin load. If endotoxin matters, it needs to be tested and reported. Go to post

post #7 answers the question as asked. The question underneath it is different.

Counter-ion form is crucial: peptides are isolated as salts, most often trifluoroacetate from reversed-phase purification or acetate after salt exchange. The counter-ion is part of the mass in the vial and is not part of the peptide. Two vials of the same purity, one as TFA and one as acetate, contain different amounts of peptide per milligram.

25 likes in reply to #2 7mo

a.amankwahTL2 Moderator14 Jan 2026#11

This follows post #8 rather than contradicting it.

Amino acid analysis gives content: it hydrolyses the peptide and quantifies the residues. It measures the peptide content independent of chromatographic purity. Very few supplier certificates report it.

32 likes 6mo

p.friskTL2 Moderator7 Mar 2026#22

This follows post #19 rather than contradicting it.

Thank you for the correction. I have edited my earlier post with a note rather than silently, so the thread still makes sense to read. The error was mine and it was the kind that comes from remembering a figure instead of looking it up.

25 likes 5mo

n.chowdhuryTL2 Moderator24 Mar 2026#26

Water content (residual moisture) matters: lyophilised peptide is not dry. A few percent water is normal. The difference between a TFA salt and an acetate salt can be several percent. Content calculations need the water content to be accurate.

18 likes 4mo

aliquot_lineTL3Regular8 May 2026#37

e.tamm, post #19: I disagree with the reply above, and I think the disagreement is substantive rather than terminological. The distinction being drawn does not survive when you look at the published data for this specific question. I would be glad to be shown wrong on this, because the version I am arguing against is more convenient. Go to post

25 likes in reply to #19 3mo

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