whats the void volume peak, is that always solvent
#hplc-massspec 2025-12-19
Friday27 messages6 participantstimes are UTC
Highlights from this day
- gip_glp_gil — two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly 18:52
- gip_glp_gil — whats a normal gradient for a peptide this size 19:07
- logrotate — follow up update from 14 months ago: switched to asking for the chromatogram rather than the number and it changed everything 19:46
- ferrous_ash — the honest position is that hobby-level interpretation of a chromatogram is worth something but not much 21:14
- back_from_away — a certificate with a number and no chromatogram is asking you to trust the integration you cannot see 22:05
thats co-elution
two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
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 substanceyou need more sample for identity than for purity. plan for that when you post it
whats a normal gradient for a peptide this size
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co-elution is the failure mode that a beautiful single peak is most likely to be hiding
run a blank
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quick one a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
follow up update from 14 months ago: switched to asking for the chromatogram rather than the number and it changed everything
thats the solvent peak
coming back after 18 months, what changed in how you read these
whats a plus one dalton shift usually
retention time is a hint
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semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2, still working it out
integration difference
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thats a charge state
ms/ms or it isnt identity
follow up nobody runs enough blanks, including me
plus sixteen, is that always oxidation
i asked PeptideMeter for the raw trace and they sent it. that is the right answer to that question
follow up is monoisotopic or average mass the one on most certificates
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
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slightly off topic but how would a truncation sequence show up
can you tell a dimer from the chromatogram alone
is a tailing factor of anything specific a problem
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
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