the retention time on this one is different from the last lot, problem
#coa-reading 2026-04-08
Wednesday44 messages9 participantstimes are UTC
Highlights from this day
- meniscus_mel — why do some certificates report to one decimal and some to two 12:41
- triumph_watch — how do you verify a certificate is actually from the lab it says 17:14
- triumph_watch — for the archive nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself, still working it out 17:56
why do some certificates report to one decimal and some to two
💀1🔥8
ok so the three way match is vial, certificate, invoice. if all three agree you have something
not evidence on its own
no lot number on this certificate, does that make it worthless
looks re-dated
whats the minimum a certificate has to have before you take it seriously
slightly off topic but two certificates from the same supplier have an identical chromatogram, is that normal
not detected means nothing
💀17👍5
residual solvents matter more than people think for anything that went through a lot of purification steps
📈2
the related substances table is the interesting part. a row of "not detected" means they did not look hard
net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
i asked KP for the method and they sent it. that alone put them ahead of most
certificate is dated before the lot date, is that just sloppiness
the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
whats the related substances table actually telling me
[edited]coming back after 4 months, has the pinned reading guide changed
one decimal versus two is usually just house style, not precision
is area percent the same thing as how many mg are in the vial
net not gross
weigh the vial
a certificate should name the method, the instrument, the column and the operator. most name none of those
the paperwork can be perfect and the vial can still be light. weigh it
🤝1
test it yourself
does purity by hplc at one wavelength miss things
gross mass on a jewellery scale plus the water content is enough to catch most underfills
thats a tell
single wavelength detection can miss a co-eluting impurity that does not absorb there
is sterility tested as part of a normal purity certificate
👍9
is endotoxin ever tested on research material
is water content normally on a certificate or do you have to ask
[edited]no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration
how do you verify a certificate is actually from the lab it says
🧪18👀10🎉2
my 10mg vial weighed more than 2mg of powder, is the certificate lying
an identical chromatogram on two different lots is the single biggest tell there is
tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance
if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not, n of 1 obviously
a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully
does anyone actually check the residual solvents section
for the archive nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself, still working it out
lot bought purity assay/label
A-2418 2025-03 99.1% 9.6 / 10mg
A-2601 2025-08 98.7% 9.8 / 10mg
B-0114 2026-01 99.3% 9.4 / 10mg
B-0329 2026-04 98.9% 9.9 / 10mgpurity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
the certificate from TFC is the one i use to teach this because it actually has a populated impurity table
[edited]mixed fonts and inconsistent kerning in one document is worth a second look
retention time shifts between runs are normal. relative retention time is the number to compare, we shall see