gross mass on a jewellery scale plus the water content is enough to catch most underfills
#coa-reading 2025-12-14
Sunday47 messages9 participantstimes are UTC
Highlights from this day
- endotoxin_ed — a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully 17:10
- salt_bridge — i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does 17:50
- salt_bridge — retention time shifts between runs are normal. relative retention time is the number to compare 20:28
no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration
tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance
is sterility tested as part of a normal purity certificate
weigh the vial
is endotoxin ever tested on research material
why do some certificates report to one decimal and some to two
unrelated but residual solvents matter more than people think for anything that went through a lot of purification steps
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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
the honest summary is that a certificate tells you what the supplier says about a lot they chose to test, take that with a pinch of salt
| 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 |
an identical chromatogram on two different lots is the single biggest tell there is
for the archive the font on this one changes halfway down, am i being paranoid
janoshik-a-2601.pdf
2 pages · 183 KB · not retained in the public archive
a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully
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i have never seen a research certificate with an endotoxin result on it. not once, i have it written down somewhere
no lot number on this certificate, does that make it worthless
is a supplier certificate worth anything on its own
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 / 10mgnet peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
tfa or acetate, how do i tell from the paperwork
i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does
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not evidence on its own
right so the related substances table is the interesting part. a row of "not detected" means they did not look hard
single wavelength detection can miss a co-eluting impurity that does not absorb there
one decimal versus two is usually just house style, not precision
is water content normally on a certificate or do you have to ask
purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
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
| 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 |
does anyone actually check the residual solvents section
ask for water content
is area percent the same thing as how many mg are in the vial
update from 11 months ago: started asking every supplier for water content and about half now include it, i think
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 / 10mgnobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself, i could be wrong
purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
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purity is not assay
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sloppy not sinister
does anyone keep a folder of certificates to compare over time
is there a standard layout or does every lab do their own
looks re-dated
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no lot no certificate
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retention time shifts between runs are normal. relative retention time is the number to compare
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good certificate actually
the paperwork can be perfect and the vial can still be light. weigh it
for the archive thats a tell
if you only read one line on a certificate, read the lot number. if you read two, read the assay, from memory
what does net peptide content mean next to gross mass
certificate is dated before the lot date, is that just sloppiness
the certificate from HJ is the one i use to teach this because it actually has a populated impurity table
check the lot
| 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 |
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test it yourself