is water content normally on a certificate or do you have to ask
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#coa-reading 2026-03-13
Friday46 messages9 participantstimes are UTC
Highlights from this day
- yyz_vial — is water content normally on a certificate or do you have to ask 21:10
- salt_bridge — the honest summary is that a certificate tells you what the supplier says about a lot they chose to test 22:18
- lena_lots — does anyone keep a folder of certificates to compare over time 22:23
- cagri_curious — should a certificate say which instrument and method they used 23:28
single wavelength detection can miss a co-eluting impurity that does not absorb there
good certificate actually
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i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does
thats the counterion
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weigh the vial
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the three way match is vial, certificate, invoice. if all three agree you have something
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
the certificate from WXT is the one i use to teach this because it actually has a populated impurity table
no lot number on this certificate, does that make it worthless
the certificate from BCH is the one i use to teach this because it actually has a populated impurity table
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Archive lookup: yyz_vial first appears in this channel on 2025-11-22.
one decimal versus two is usually just house style, not precision
right so the related substances table is the interesting part. a row of "not detected" means they did not look hard
the related substances table is the interesting part. a row of "not detected" means they did not look hard
test it yourself
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sterility and endotoxin are separate tests and almost nobody runs either on research material
i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does
not evidence on its own
whats the minimum a certificate has to have before you take it seriously
[edited]if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not
right so a certificate should name the method, the instrument, the column and the operator. most name none of those, for what its worth
tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance, ymmv
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
no lot no certificate
is sterility tested as part of a normal purity certificate
ask for water content
does purity by hplc at one wavelength miss things
the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
peak RRT area% note
1 0.42 0.31 solvent front
2 0.88 0.44 related substance
3 1.00 98.72 main
4 1.14 0.53 related substancean identical chromatogram on two different lots is the single biggest tell there is
a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists
does anyone keep a folder of certificates to compare over time
| 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 |
i asked HJ for the method and they sent it. that alone put them ahead of most
thats a tell
purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
Reminder for karl_fischer: dose day is today. Set 8 days ago.
net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
thats a real table
gross mass on a jewellery scale plus the water content is enough to catch most underfills
unrelated but certificate is dated before the lot date, is that just sloppiness
looks re-dated
sloppy not sinister
whats the related substances table actually telling me
purity is not assay
sorry to jump in looks re-dated
how do you verify a certificate is actually from the lab it says
should a certificate say which instrument and method they used
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nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself, i could be wrong