nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself
| 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 |
update from 9 months ago: started asking every supplier for water content and about half now include it
a certificate should name the method, the instrument, the column and the operator. most name none of those
the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
test it yourself
the font on this one changes halfway down, am i being paranoid
weigh the vial
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 related substances table is the interesting part. a row of "not detected" means they did not look hard
an identical chromatogram on two different lots is the single biggest tell there is
ok so a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully
the retention time on this one is different from the last lot, problem
looks re-dated
Recon calculator: 10mg in 3ml = 2.5mg/ml.
residual solvents matter more than people think for anything that went through a lot of purification steps
not detected means nothing
sterility and endotoxin are separate tests and almost nobody runs either on research material
one decimal versus two is usually just house style, not precision
Digest for the week of 2026-01-16 has been published.
net not gross
sorry to jump in mixed fonts and inconsistent kerning in one document is worth a second look
gross mass on a jewellery scale plus the water content is enough to catch most underfills
*Medutest not the other one
update on the earlier thing coming back after 17 months, has the pinned reading guide changed
purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
retention time shifts between runs are normal. relative retention time is the number to compare
residual solvents matter more than people think for anything that went through a lot of purification steps
*that should say weekly
quick one how do you verify a certificate is actually from the lab it says
[edited]follow up two certificates from the same supplier have an identical chromatogram, is that normal
if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not
why would a vial be 99.2 pure and still assay under label
no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration
is endotoxin ever tested on research material
coming back to this is a supplier certificate worth anything on its own
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
ask for water content
good certificate actually
single wavelength detection can miss a co-eluting impurity that does not absorb there
i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does
same chromatogram
i keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019
update on the earlier thing water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it