weigh the vial
[edited]#coa-reading 2026-01-22
Thursday44 messages9 participantstimes are UTC
Highlights from this day
- comment_fatigue — net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial 22:28
- comment_fatigue — a certificate should name the method, the instrument, the column and the operator. most name none of those 22:30
- LC_MS_Lena — one decimal versus two is usually just house style, not precision, n of 1 obviously 22:47
- HPLC_Hank — update from 23 months ago: started asking every supplier for water content and about half now include it 23:03
- blank_run — residual solvents matter more than people think for anything that went through a lot of purification steps 23:58
coming back after 25 months, has the pinned reading guide changed
follow up whats the minimum a certificate has to have before you take it seriously
thats a real table
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net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
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a certificate should name the method, the instrument, the column and the operator. most name none of those
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does anyone keep a folder of certificates to compare over time
the certificate from WWB is the one i use to teach this because it actually has a populated impurity table
not detected means nothing
thats a tell
a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully
water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it, i could be wrong
looks re-dated
one decimal versus two is usually just house style, not precision, n of 1 obviously
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if the certificate date precedes the lot date, ask. sometimes it is sloppiness and sometimes it is not
no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration
sloppy not sinister
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same chromatogram
the related substances table is the interesting part. a row of "not detected" means they did not look hard
what does net peptide content mean next to gross mass
retention time shifts between runs are normal. relative retention time is the number to compare
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not evidence on its own
if you only read one line on a certificate, read the lot number. if you read two, read the assay
update from 23 months ago: started asking every supplier for water content and about half now include it
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purity is not assay
does anyone actually check the residual solvents section
an identical chromatogram on two different lots is the single biggest tell there is
sorry to jump in is water content normally on a certificate or do you have to ask
two certificates from the same supplier have an identical chromatogram, is that normal
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sterility and endotoxin are separate tests and almost nobody runs either on research material
a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists
i asked JEEP for the method and they sent it. that alone put them ahead of most, take that with a pinch of salt
*that should say weekly
no lot no certificate
purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
does purity by hplc at one wavelength miss things
thats the counterion
i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does
tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance
i keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019
[edited]slightly off topic but why do some certificates report to one decimal and some to two
good certificate actually
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
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