the related substances table is the interesting part. a row of "not detected" means they did not look hard, thats just me
#coa-reading 2025-01-04
Saturday43 messages10 participantstimes are UTC
Highlights from this day
- factory_direct_fi — no lot number on this certificate, does that make it worthless 12:23
- two_labs_two_answers — the certificate from WXT is the one i use to teach this because it actually has a populated impurity table 12:59
- VialBot — Recon calculator: 2mg in 1.5ml = 8mg/ml. 13:43
- evidence_or_not — why would a vial be 96.8 pure and still assay under label 15:49
- evidence_or_not — purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions, anyway nobody can authenticate a certificate from… 15:52
unrelated but sterility and endotoxin are separate tests and almost nobody runs either on research material, ask me again in a month
does purity by hplc at one wavelength miss things
is endotoxin ever tested on research material
water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it
does anyone keep a folder of certificates to compare over time
single wavelength detection can miss a co-eluting impurity that does not absorb there
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nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself, still working it out
no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration, thats just me
retention time shifts between runs are normal. relative retention time is the number to compare
no lot number on this certificate, does that make it worthless
| 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 |
an identical chromatogram on two different lots is the single biggest tell there is
check the lot
should a certificate say which instrument and method they used
the certificate from WXT is the one i use to teach this because it actually has a populated impurity table
two certificates from the same supplier have an identical chromatogram, is that normal
i have never seen a research certificate with an endotoxin result on it. not once
update from 20 months ago: started asking every supplier for water content and about half now include it
how do you verify a certificate is actually from the lab it says
thats a tell
Recon calculator: 2mg in 1.5ml = 8mg/ml.
a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists, not advice obviously
the three way match is vial, certificate, invoice. if all three agree you have something
residual solvents matter more than people think for anything that went through a lot of purification steps
one decimal versus two is usually just house style, not precision, from memory
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
quick one if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not
tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance
whats the related substances table actually telling me
thats the counterion
if you only read one line on a certificate, read the lot number. if you read two, read the assay, someone check my working
whats the minimum a certificate has to have before you take it seriously
the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully, still working it out
good certificate actually
why would a vial be 96.8 pure and still assay under label
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i keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019
purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions, anyway
nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself
a certificate should name the method, the instrument, the column and the operator. most name none of those
mixed fonts and inconsistent kerning in one document is worth a second look
what does net peptide content mean next to gross mass
net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial