net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
#coa-reading 2025-05-16
Friday33 messages7 participantstimes are UTC
Highlights from this day
- acetate_ash — nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself, take that with a pinch of salt 15:39
- LC_MS_Lena — does anyone keep a folder of certificates to compare over time 17:08
- lead_time_lars — whats the minimum a certificate has to have before you take it seriously 18:06
- peak_split — residual solvents matter more than people think for anything that went through a lot of purification steps 18:36
what does net peptide content mean next to gross mass
check the lot
tfa counterion runs higher by mass than acetate. if the certificate does not say, you cannot do the mass balance, from memory
sloppy not sinister
looks re-dated
i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does
i have never seen a research certificate with an endotoxin result on it. not once
how do you verify a certificate is actually from the lab it says
the three way match is vial, certificate, invoice. if all three agree you have something
nobody can authenticate a certificate from a scan. you authenticate the material by testing it yourself, take that with a pinch of salt
gradient_gregi was wrong about this for a year: area percent under-reports nothing, it just answers…
a certificate should name the method, the instrument, the column and the operator. most name none of those
same chromatogram
if you only read one line on a certificate, read the lot number. if you read two, read the assay
is sterility tested as part of a normal purity certificate
two certificates from the same supplier have an identical chromatogram, is that normal
not evidence on its own
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does anyone keep a folder of certificates to compare over time
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 substanceretention time shifts between runs are normal. relative retention time is the number to compare
ask for water content
why would a vial be 99.4 pure and still assay under label
back_from_awaythe three way match is vial, certificate, invoice. if all three agree you have something
does purity by hplc at one wavelength miss things
mixed fonts and inconsistent kerning in one document is worth a second look
right so single wavelength detection can miss a co-eluting impurity that does not absorb there
no lot no certificate
| 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 |
sorry to jump in an identical chromatogram on two different lots is the single biggest tell there is
tfa or acetate, how do i tell from the paperwork
thats the counterion
not detected means nothing
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whats the minimum a certificate has to have before you take it seriously
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no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration, still working it out
one decimal versus two is usually just house style, not precision
residual solvents matter more than people think for anything that went through a lot of purification steps
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