ask for water content
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#coa-reading 2026-05-20
Wednesday56 messages9 participantstimes are UTC
Highlights from this day
- mira_pins — while im here certificate is dated before the lot date, is that just sloppiness 18:57
- pinch_not_stretch — while im here the certificate from MKM is the one i use to teach this because it actually has a populated impurity table 19:25
- power_through_no — if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not 19:34
- retention_time — a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists 20:02
follow up purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
thats a real table
net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
does purity by hplc at one wavelength miss things
the related substances table is the interesting part. a row of "not detected" means they did not look hard
i have never seen a research certificate with an endotoxin result on it. not once
looks re-dated
[edited]not detected means nothing
sterility and endotoxin are separate tests and almost nobody runs either on research material
for the archive should a certificate say which instrument and method they used
the three way match is vial, certificate, invoice. if all three agree you have something
the paperwork can be perfect and the vial can still be light. weigh it
tfa or acetate, how do i tell from the paperwork
i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does
ok so tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance
quick one water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it, happy to be corrected
while im here certificate is dated before the lot date, is that just sloppiness
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 substancewhy do some certificates report to one decimal and some to two
test it yourself
[edited]follow up if you only read one line on a certificate, read the lot number. if you read two, read the assay
sorry to jump in i keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019
not evidence on its own
while im here the certificate from MKM is the one i use to teach this because it actually has a populated impurity table
how do you verify a certificate is actually from the lab it says
if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not
| 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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residual solvents matter more than people think for anything that went through a lot of purification steps
is area percent the same thing as how many mg are in the vial
*Janoshik not the other one
pinch_not_stretchfollow up if you only read one line on a certificate, read the lot number. if you read…
is a supplier certificate worth anything on its own
i asked SSA for the method and they sent it. that alone put them ahead of most
is sterility tested as part of a normal purity certificate
residual solvents matter more than people think for anything that went through a lot of purification steps
no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration
the three way match is vial, certificate, invoice. if all three agree you have something
a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists
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net not gross
coming back to this is there a standard layout or does every lab do their own
quick one why would a vial be 98.1 pure and still assay under label
no lot no certificate, n of 1 obviously
the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
thats the counterion
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an identical chromatogram on two different lots is the single biggest tell there is
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
a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully
mixed fonts and inconsistent kerning in one document is worth a second look, from memory
single wavelength detection can miss a co-eluting impurity that does not absorb there
sloppy not sinister
retention time shifts between runs are normal. relative retention time is the number to compare, ask me again in a month
ok so nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself
is endotoxin ever tested on research material
thats a tell, ill dig out the number
the certificate from WXT is the one i use to teach this because it actually has a populated impurity table
purity is not assay
weigh the vial
does anyone keep a folder of certificates to compare over time
what does net peptide content mean next to gross mass
ok so coming back after 2 months, has the pinned reading guide changed
good certificate actually