coming back after 9 months, has the pinned reading guide changed
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#coa-reading 2026-05-15
Friday26 messages8 participantstimes are UTC
Highlights from this day
- HPLC_Hank — the honest summary is that a certificate tells you what the supplier says about a lot they chose to test 22:19
- LC_MS_Lena — purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions 23:11
- LC_MS_Lena — is there a standard layout or does every lab do their own 23:14
- LC_MS_Lena — quick one the related substances table is the interesting part. a row of "not detected" means they did not look hard 23:26
the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
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the retention time on this one is different from the last lot, problem
not evidence on its own
a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists
does purity by hplc at one wavelength miss things
single wavelength detection can miss a co-eluting impurity that does not absorb there
chromatogram-overlay.png
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test it yourself
tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance
mixed fonts and inconsistent kerning in one document is worth a second look
Digest for the week of 2025-10-22 has been published.
an identical chromatogram on two different lots is the single biggest tell there is
follow up a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully
purity is not assay
not detected means nothing
the font on this one changes halfway down, am i being paranoid
sterility and endotoxin are separate tests and almost nobody runs either on research material
sorry to jump in what does net peptide content mean next to gross mass
weigh the vial
thats the counterion
purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
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one decimal versus two is usually just house style, not precision
is there a standard layout or does every lab do their own
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why do some certificates report to one decimal and some to two
quick one the related substances table is the interesting part. a row of "not detected" means they did not look hard
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if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not
two certificates from the same supplier have an identical chromatogram, is that normal