looks re-dated
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#coa-reading 2025-02-12
Wednesday31 messages9 participantstimes are UTC
Highlights from this day
- void_volume — update on the earlier thing 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, from memory 16:41
- pbs_pip — the related substances table is the interesting part. a row of "not detected" means they did not look hard 16:49
- HPLC_Hank — the certificate from GL Biochem is the one i use to teach this because it actually has a populated impurity table 17:26
no lot no certificate
a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully
update on the earlier thing my 15mg vial weighed more than 15mg of powder, is the certificate lying
sorry to jump in no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration
nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself
residual solvents matter more than people think for anything that went through a lot of purification steps
the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
thats the counterion
an identical chromatogram on two different lots is the single biggest tell there is
coming back after 9 months, has the pinned reading guide changed
update on the earlier thing 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, from memory
thats a tell
does purity by hplc at one wavelength miss things
not evidence on its own
the related substances table is the interesting part. a row of "not detected" means they did not look hard
| 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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update from 19 months ago: started asking every supplier for water content and about half now include it
coming back to this tfa or acetate, how do i tell from the paperwork
sterility and endotoxin are separate tests and almost nobody runs either on research material
does anyone keep a folder of certificates to compare over time
ask for water content
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why would a vial be 96.8 pure and still assay under label
the certificate from GL Biochem is the one i use to teach this because it actually has a populated impurity table
retention time shifts between runs are normal. relative retention time is the number to compare
purity is not assay
good certificate actually
sloppy not sinister
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is area percent the same thing as how many mg are in the vial
one decimal versus two is usually just house style, not precision, for what its worth
quick one i keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019