update from 4 months ago: started asking every supplier for water content and about half now include it
#coa-reading 2026-04-29
Wednesday55 messages13 participantstimes are UTC
Highlights from this day
- void_volume — 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 20:34
- void_volume — the honest summary is that a certificate tells you what the supplier says about a lot they chose to test 20:43
- area_percent — update on the earlier thing i keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019, ill dig out the number 21:22
- noct.titrate — update on the earlier thing whats the minimum a certificate has to have before you take it seriously 23:26
net not gross
purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
[edited]if you only read one line on a certificate, read the lot number. if you read two, read the assay
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
💀1😂2🎉16
test it yourself
good certificate actually
van_isle_vialif you only read one line on a certificate, read the lot number. if you read two, read…
the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
📈5🧊9📉12
retention time shifts between runs are normal. relative retention time is the number to compare
a certificate should name the method, the instrument, the column and the operator. most name none of those
gross mass on a jewellery scale plus the water content is enough to catch most underfills
no lot no certificate
🔥9✅2👍7
my 2mg vial weighed more than 5mg of powder, is the certificate lying
quick one the paperwork can be perfect and the vial can still be light. weigh it, ymmv
not evidence on its own
the certificate from TFC is the one i use to teach this because it actually has a populated impurity table
i have never seen a research certificate with an endotoxin result on it. not once
🔥14✅1
Testing queue: 8 submissions open, 108 awaiting dispatch.
not detected means nothing
nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself
right so water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it
update on the earlier thing i keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019, ill dig out the number
😂5❤️9💀7
one decimal versus two is usually just house style, not precision
check the lot
tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance
purity is not assay
[edited]Verification log updated: MKM — evidence added, status unchanged.
same chromatogram
[edited]residual solvents matter more than people think for anything that went through a lot of purification steps
*that should say weekly
if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not
the related substances table is the interesting part. a row of "not detected" means they did not look hard
🤝2🔥6
right so is endotoxin ever tested on research material
purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists
*VendorInvestigate not the other one
for the archive single wavelength detection can miss a co-eluting impurity that does not absorb there
✅3
sorry to jump in sterility and endotoxin are separate tests and almost nobody runs either on research material
how do you verify a certificate is actually from the lab it says
weigh the vial
no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration, n of 1 obviously
looks re-dated
update on the earlier thing a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully, for what its worth
i asked TFC for the method and they sent it. that alone put them ahead of most
why do some certificates report to one decimal and some to two
thats a real table
📉1
sloppy not sinister
does purity by hplc at one wavelength miss things
peak RRT area% note
1 0.42 0.31 solvent front
2 0.88 0.44 related substance
3 1.00 98.72 main
4 1.14 0.53 related substancelooks re-dated
👍14
coming back after 8 months, has the pinned reading guide changed
does anyone actually check the residual solvents section
why would a vial be 99.2 pure and still assay under label
🙏7💀18🧪14
weigh the vial
is there a standard layout or does every lab do their own
the three way match is vial, certificate, invoice. if all three agree you have something
retention time shifts between runs are normal. relative retention time is the number to compare
update on the earlier thing whats the minimum a certificate has to have before you take it seriously
| 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 |
🙏4