need more sample
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#hplc-massspec 2026-06-20
Saturday21 messages5 participantstimes are UTC
Highlights from this day
- a1c_lag — i was wrong about tailing factor. it is usually the injection or the pH, not the column 22:13
- auckland_aliquot — i asked VendorInvestigate for the raw trace and they sent it. that is the right answer to that question 22:50
- auckland_aliquot — semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2 23:28
is uv at 214 or 280 better for peptides
thats co-elution
follow up ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
thats a charge state
plus 0.98 is deamidation
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plus 16 is oxidation
[edited]the first peak is the solvent. it is always the solvent
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update on the earlier thing a certificate with a number and no chromatogram is asking you to trust the integration you cannot see, thats just me
[edited]does retention time on its own tell you what the compound is
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result, thats just me
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
i was wrong about tailing factor. it is usually the injection or the pH, not the column
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214nm sees the amide backbone so it sees everything. 280 only sees aromatics
if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
lot-log.csv
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thats the solvent peak
update on the earlier thing relative retention time against a standard is comparable between labs. absolute minutes are not
i asked VendorInvestigate for the raw trace and they sent it. that is the right answer to that question
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for the archive i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
fridge-thermometer.png
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semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
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the honest position is that hobby-level interpretation of a chromatogram is worth something but not much