the paperwork can be perfect and the vial can still be light. weigh it
#coa-reading 2025-10-03
Friday47 messages10 participantstimes are UTC
Highlights from this day
- new_here_nat — nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself 21:56
- acetate_ash — the honest summary is that a certificate tells you what the supplier says about a lot they chose to test 22:30
- karl_fischer — why would a vial be 96.8 pure and still assay under label 23:17
net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
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ok so why do some certificates report to one decimal and some to two
i asked QSC for the method and they sent it. that alone put them ahead of most
my 20mg vial weighed more than 2mg of powder, is the certificate lying
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not evidence on its own
one decimal versus two is usually just house style, not precision
the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists
single wavelength detection can miss a co-eluting impurity that does not absorb there
mixed fonts and inconsistent kerning in one document is worth a second look
unrelated but i keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019
if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not
lot-log.csv
917 rows · not retained in the public archive
test it yourself
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the font on this one changes halfway down, am i being paranoid
purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
quick one a certificate should name the method, the instrument, the column and the operator. most name none of those
right so an identical chromatogram on two different lots is the single biggest tell there is
does anyone keep a folder of certificates to compare over time
is water content normally on a certificate or do you have to ask
i have never seen a research certificate with an endotoxin result on it. not once
no lot no certificate
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the certificate from TFC is the one i use to teach this because it actually has a populated impurity table
check the lot
a vial can be 99.4% pure and hold 8.1mg of a 10mg label. both numbers are true and only one of them is the one you care about
tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance
thats a real table
not detected means nothing
nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself
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while im here the three way match is vial, certificate, invoice. if all three agree you have something
thats a tell
sterility and endotoxin are separate tests and almost nobody runs either on research material
quick one no lot number on this certificate, does that make it worthless
whats the related substances table actually telling me
water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it
no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration
the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
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purity is not assay
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genuine question gross mass on a jewellery scale plus the water content is enough to catch most underfills
thats the counterion
update from 12 months ago: started asking every supplier for water content and about half now include it
good certificate actually
sloppy not sinister
why would a vial be 96.8 pure and still assay under label
| Line | Claims | Does not claim |
|---|---|---|
| Purity (area %) | fraction of detected material that is the target | how many mg are in the vial |
| Assay / content | mg of target per vial | that it is sterile |
| Water content | mass fraction that is water | anything about purity |
| Counterion | salt form and its mass share | net peptide unless stated |
| Related substances | what else was seen | what was not looked for |
weigh the vial
net not gross