the certificate from WXT is the one i use to teach this because it actually has a populated impurity table
#coa-reading 2026-06-05
Friday25 messages5 participantstimes are UTC
Highlights from this day
- LC_MS_Lena — retention time shifts between runs are normal. relative retention time is the number to compare 20:28
- LC_MS_Lena — the font on this one changes halfway down, am i being paranoid 20:29
- LC_MS_Lena — an identical chromatogram on two different lots is the single biggest tell there is, thats just me 20:54
- LC_MS_Lena — i asked QSC for the method and they sent it. that alone put them ahead of most 21:17
- void_volume — the retention time on this one is different from the last lot, problem 21:39
no lot number on this certificate, does that make it worthless
quick one is there a standard layout or does every lab do their own
retention time shifts between runs are normal. relative retention time is the number to compare
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the font on this one changes halfway down, am i being paranoid
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a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists
sterility and endotoxin are separate tests and almost nobody runs either on research material, someone check my working
sloppy not sinister
an identical chromatogram on two different lots is the single biggest tell there is, thats just me
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thats a real table
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 substanceshould a certificate say which instrument and method they used
does anyone actually check the residual solvents section
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no lot no certificate
residual solvents matter more than people think for anything that went through a lot of purification steps
i asked QSC for the method and they sent it. that alone put them ahead of most
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how do you verify a certificate is actually from the lab it says
the paperwork can be perfect and the vial can still be light. weigh it
i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does
single wavelength detection can miss a co-eluting impurity that does not absorb there
the retention time on this one is different from the last lot, problem
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right so whats the minimum a certificate has to have before you take it seriously
good certificate actually
thats the counterion
is sterility tested as part of a normal purity certificate
is water content normally on a certificate or do you have to ask
| 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 |