update from 10 months ago: switched to asking for the chromatogram rather than the number and it changed everything, for what its worth
#hplc-massspec 2026-03-01
Sunday25 messages5 participantstimes are UTC
Highlights from this day
- no_appetite_nia — a shoulder on a peak is information, and usually bad information 13:34
- no_appetite_nia — co-elution is the failure mode that a beautiful single peak is most likely to be hiding, i think 13:35
- fasting_insulin — how much sample does a lab actually need for identity as well as purity 15:15
follow up whats the void volume peak, is that always solvent
within inter-lab range
shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
how do you tell co-elution from a clean single peak
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
my peak has a shoulder on it, what does that usually mean
shallow gradient
truncations show as a mass deficit matching one or more residues. you need the sequence to say which
ask for the trace
does retention time on its own tell you what the compound is
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the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
a shoulder on a peak is information, and usually bad information
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co-elution is the failure mode that a beautiful single peak is most likely to be hiding, i think
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genuine question has anyone ever had a result where the mass was right and the purity was wrong
thats co-elution
is monoisotopic or average mass the one on most certificates
peptidemeter-summary-f-1330.pdf
2 pages · 727 KB · not retained in the public archive
how much sample does a lab actually need for identity as well as purity
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unrelated but i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
if the lab reports area percent without stating the wavelength, the number is less useful than it looks
while im here oxidation is about plus 15.99 Da and is usually methionine or tryptophan
the first peak is the solvent. it is always the solvent
semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
ms/ms or it isnt identity