single wavelength detection can miss a co-eluting impurity that does not absorb there
#coa-reading 2025-05-21
Wednesday31 messages7 participantstimes are UTC
Highlights from this day
- dexa_or_bia — the retention time on this one is different from the last lot, problem 22:13
- area_percent — sorry to jump in mixed fonts and inconsistent kerning in one document is worth a second look 22:19
- truncation_tru — genuine question the font on this one changes halfway down, am i being paranoid 22:31
- chain_of_custody — quick one purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions 22:52
looks re-dated
ok so the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
should a certificate say which instrument and method they used
net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
is water content normally on a certificate or do you have to ask
the related substances table is the interesting part. a row of "not detected" means they did not look hard
the retention time on this one is different from the last lot, problem
📉13👀1
purity is not assay
sorry to jump in mixed fonts and inconsistent kerning in one document is worth a second look
👀9🔥3⚠️1
no lot no certificate
same chromatogram
genuine question the font on this one changes halfway down, am i being paranoid
👀18📉1🧊16
two certificates from the same supplier have an identical chromatogram, is that normal
i asked GL Biochem for the method and they sent it. that alone put them ahead of most
the certificate from FGP is the one i use to teach this because it actually has a populated impurity table
coming back to this if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not, i think
good certificate actually
quick one purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
🤝18🧊15⚠️1
water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it
i have never seen a research certificate with an endotoxin result on it. not once
i keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019
check the lot
is sterility tested as part of a normal purity certificate
weigh the vial
tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance
sloppy not sinister
🧊12
for the archive certificate is dated before the lot date, is that just sloppiness
⚠️9🧪2
slightly off topic but whats the minimum a certificate has to have before you take it seriously
ask for water content
i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does, happy to be corrected
📈4