sterility and endotoxin are separate tests and almost nobody runs either on research material
residual solvents matter more than people think for anything that went through a lot of purification steps
#coa-reading 2026-06-18
Thursday55 messages12 participantstimes are UTC
Highlights from this day
- cold_pack_carla — if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not 22:03
- gorse_gains — an identical chromatogram on two different lots is the single biggest tell there is 23:05
- two_ml_two — whats the related substances table actually telling me 23:08
- logrotate — the paperwork can be perfect and the vial can still be light. weigh it 23:37
- logrotate — a certificate should name the method, the instrument, the column and the operator. most name none of those 23:58
the related substances table is the interesting part. a row of "not detected" means they did not look hard
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test it yourself
fridge-temps.csv
413 rows · not retained in the public archive
if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not
chromatogram-overlay.png
1240 × 720 · 365 KB · not retained in the public archive
nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself
is there a standard layout or does every lab do their own
residual solvents matter more than people think for anything that went through a lot of purification steps
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the honest summary is that a certificate tells you what the supplier says about a lot they chose to test, your mileage will differ
purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions, ymmv
tfa or acetate, how do i tell from the paperwork
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i asked JEEP for the method and they sent it. that alone put them ahead of most
no lot number on this certificate, does that make it worthless
whats the minimum a certificate has to have before you take it seriously
good certificate actually
not detected means nothing
does anyone actually check the residual solvents section
i have never seen a research certificate with an endotoxin result on it. not once
tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance, ask me again in a month
[edited]follow up 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
sloppy not sinister
retention time shifts between runs are normal. relative retention time is the number to compare, not advice obviously
i asked WWB for the method and they sent it. that alone put them ahead of most
purity is not assay
unrelated but the certificate from QST is the one i use to teach this because it actually has a populated impurity table, i think
right so does purity by hplc at one wavelength miss things
thats a tell
the three way match is vial, certificate, invoice. if all three agree you have something
i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does
quick one why do some certificates report to one decimal and some to two
[edited]not evidence on its own
[edited]update from 15 months ago: started asking every supplier for water content and about half now include it
a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists, thats just me
coming back after 23 months, has the pinned reading guide changed
while im here i keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019
thats a real table
quick one net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
thats the counterion
an identical chromatogram on two different lots is the single biggest tell there is
whats the related substances table actually telling me
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a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully
Digest for the week of 2025-12-26 has been published.
if you only read one line on a certificate, read the lot number. if you read two, read the assay
one decimal versus two is usually just house style, not precision
no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration, for what its worth
should a certificate say which instrument and method they used
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is endotoxin ever tested on research material
no lot no certificate
coming back to this how do you verify a certificate is actually from the lab it says
ask for water content, thats one data point
the paperwork can be perfect and the vial can still be light. weigh it
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check the lot
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ok so 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
a certificate should name the method, the instrument, the column and the operator. most name none of those
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