slightly off topic but the related substances table is the interesting part. a row of "not detected" means they did not look hard, thats one data point
#coa-reading 2026-06-10
Wednesday52 messages11 participantstimes are UTC
Highlights from this day
- tga_notice — sorry to jump in does anyone actually check the residual solvents section 16:56
- tyne_tracks — slightly off topic but tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance 17:22
- ten_of_ten — residual solvents matter more than people think for anything that went through a lot of purification steps 18:06
- batch_bandit — the three way match is vial, certificate, invoice. if all three agree you have something, i could be wrong 18:16
- retention_time — sorry to jump in purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions, happy to be corrected 19:37
my 20mg vial weighed more than 5mg of powder, is the certificate lying
net not gross
i asked GGPeps for the method and they sent it. that alone put them ahead of most
single wavelength detection can miss a co-eluting impurity that does not absorb there
what does net peptide content mean next to gross mass
[edited]sorry to jump in does anyone actually check the residual solvents section
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should a certificate say which instrument and method they used
nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself
net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial, ask me again in a month
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
slightly off topic but tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance
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thats the counterion
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the paperwork can be perfect and the vial can still be light. weigh it
whats the minimum a certificate has to have before you take it seriously
a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists
is a supplier certificate worth anything on its own
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an identical chromatogram on two different lots is the single biggest tell there is
a certificate should name the method, the instrument, the column and the operator. most name none of those
the retention time on this one is different from the last lot, problem
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the certificate from WWB is the one i use to teach this because it actually has a populated impurity table
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the honest summary is that a certificate tells you what the supplier says about a lot they chose to test
whats the related substances table actually telling me
good certificate actually
does purity by hplc at one wavelength miss things
residual solvents matter more than people think for anything that went through a lot of purification steps
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 substanceif you only read one line on a certificate, read the lot number. if you read two, read the assay
i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does
same chromatogram
genuine question does anyone keep a folder of certificates to compare over time
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the three way match is vial, certificate, invoice. if all three agree you have something, i could be wrong
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i have never seen a research certificate with an endotoxin result on it. not once
gross mass on a jewellery scale plus the water content is enough to catch most underfills
the three way match is vial, certificate, invoice. if all three agree you have something
a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully
sloppy not sinister
retention time shifts between runs are normal. relative retention time is the number to compare
update from 18 months ago: started asking every supplier for water content and about half now include it
two certificates from the same supplier have an identical chromatogram, is that normal
is sterility tested as part of a normal purity certificate
the font on this one changes halfway down, am i being paranoid
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coming back after 13 months, has the pinned reading guide changed
why do some certificates report to one decimal and some to two
certificate is dated before the lot date, is that just sloppiness
sorry to jump in purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions, happy to be corrected
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why would a vial be 98.1 pure and still assay under label
net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
sterility and endotoxin are separate tests and almost nobody runs either on research material
genuine question mixed fonts and inconsistent kerning in one document is worth a second look, happy to be corrected
is area percent the same thing as how many mg are in the vial
one decimal versus two is usually just house style, not precision
no lot no certificate
i keep every certificate in a dated folder and compare them. two suppliers had not changed their template since 2019
water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it