a certificate should name the method, the instrument, the column and the operator. most name none of those
#coa-reading 2026-02-16
Monday23 messages7 participantstimes are UTC
Highlights from this day
- lead_time_lars — a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists 20:32
- truncation_tru — a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully 21:37
- VialBot — Digest for the week of 2026-01-02 has been published. 22:28
i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does
a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists
| 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 |
sloppy not sinister
the related substances table is the interesting part. a row of "not detected" means they did not look hard, i could be wrong
unrelated but i have never seen a research certificate with an endotoxin result on it. not once
water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it
while im here if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not
net not gross
the retention time on this one is different from the last lot, problem
the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
not evidence on its own
weigh the vial
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a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully
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tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance
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is endotoxin ever tested on research material
ask for water content
why would a vial be 99.4 pure and still assay under label
the certificate from MKM is the one i use to teach this because it actually has a populated impurity table
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Digest for the week of 2026-01-02 has been published.
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coming back to this why do some certificates report to one decimal and some to two
unrelated but the paperwork can be perfect and the vial can still be light. weigh it
thats a tell
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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