retention time shifts between runs are normal. relative retention time is the number to compare
#coa-reading 2025-05-23
Friday32 messages7 participantstimes are UTC
Highlights from this day
- point_two_five — residual solvents matter more than people think for anything that went through a lot of purification steps 17:24
- point_two_five — whats the minimum a certificate has to have before you take it seriously 17:27
- truncation_tru — unrelated but nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself 17:28
- perth_pin — the retention time on this one is different from the last lot, problem 18:22
- lyophile_liv — the certificate from FGP is the one i use to teach this because it actually has a populated impurity table 20:51
mixed fonts and inconsistent kerning in one document is worth a second look
is a supplier certificate worth anything on its own
ok so an identical chromatogram on two different lots is the single biggest tell there is
*Janoshik not the other one
residual solvents matter more than people think for anything that went through a lot of purification steps
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1000 × 700 · 910 KB · not retained in the public archive
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whats the minimum a certificate has to have before you take it seriously
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unrelated but nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself
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unrelated but is area percent the same thing as how many mg are in 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
sterility and endotoxin are separate tests and almost nobody runs either on research material
the retention time on this one is different from the last lot, problem
| 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 keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019
what does net peptide content mean next to gross mass
looks re-dated
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is endotoxin ever tested on research material
water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it, anyway
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, not advice obviously
net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
sorry to jump in 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
purity is not assay
tfa or acetate, how do i tell from the paperwork
i asked KP for the method and they sent it. that alone put them ahead of most
is water content normally on a certificate or do you have to ask
thats a tell
the certificate from FGP is the one i use to teach this because it actually has a populated impurity table
not evidence on its own
gross mass on a jewellery scale plus the water content is enough to catch most underfills