thats co-elution
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#hplc-massspec 2025-02-20
Thursday28 messages7 participantstimes are UTC
Highlights from this day
- vacuum_vic — does retention time on its own tell you what the compound is 18:54
- gradient_greg — slightly off topic but relative retention time against a standard is comparable between labs. absolute minutes are not 19:23
- monoisotopic — follow up if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic, we shall see 19:53
- monoisotopic — i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer 21:08
- salt_bridge — genuine question if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result 21:14
does ms/ms actually prove identity or just make it very likely
has anyone ever had a result where the mass was right and the purity was wrong
can you tell a dimer from the chromatogram alone
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
slightly off topic but baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
does retention time on its own tell you what the compound is
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plus sixteen, is that always oxidation
my peak has a shoulder on it, what does that usually mean
slightly off topic but relative retention time against a standard is comparable between labs. absolute minutes are not
if the lab reports area percent without stating the wavelength, the number is less useful than it looks
ms/ms or it isnt identity
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a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
update from 2 months ago: switched to asking for the chromatogram rather than the number and it changed everything
follow up if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic, we shall see
oxidation is about plus 15.99 Da and is usually methionine or tryptophan
i was wrong about tailing factor. it is usually the injection or the pH, not the column
integration choices move the number by a few tenths easily. that is most of your inter-lab variance
plus 16 is oxidation
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integration difference
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a shoulder on a peak is information, and usually bad information
retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily
i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
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need more sample
i asked Medutest for the raw trace and they sent it. that is the right answer to that question
*that should say weekly
genuine question if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
*PeptideMeter not the other one