if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not
#coa-reading 2026-06-03
Wednesday27 messages5 participantstimes are UTC
Highlights from this day
- bac_water_bill — net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial 17:00
- lisbon_lot — if you only read one line on a certificate, read the lot number. if you read two, read the assay, take that with a pinch of salt 18:18
- chain_of_custody — tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance 18:45
- chain_of_custody — water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it, ymmv 19:21
- chain_of_custody — the related substances table is the interesting part. a row of "not detected" means they did not look hard 19:36
coming back to this is area percent the same thing as how many mg are in the vial
good certificate actually
net not gross
😂11👍9
net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
single wavelength detection can miss a co-eluting impurity that does not absorb there
not evidence on its own
medutest-report-a-2601.pdf
3 pages · 555 KB · not retained in the public archive
no lot no certificate
| 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 |
looks re-dated
what does net peptide content mean next to gross mass
the three way match is vial, certificate, invoice. if all three agree you have something
does anyone keep a folder of certificates to compare over time
if you only read one line on a certificate, read the lot number. if you read two, read the assay, take that with a pinch of salt
📉1🤝6
an identical chromatogram on two different lots is the single biggest tell there is
*Medutest not the other one
tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance
update from 25 months ago: started asking every supplier for water content and about half now include it
no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration
certificate is dated before the lot date, is that just sloppiness
water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it, ymmv
❤️4
is endotoxin ever tested on research material
is sterility tested as part of a normal purity certificate
a certificate should name the method, the instrument, the column and the operator. most name none of those
the related substances table is the interesting part. a row of "not detected" means they did not look hard
❤️1📉7👍1
the retention time on this one is different from the last lot, problem
retention time shifts between runs are normal. relative retention time is the number to compare
should a certificate say which instrument and method they used