semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
#hplc-massspec 2026-03-31
Tuesday24 messages8 participantstimes are UTC
Highlights from this day
- VialBot — Verification log updated: QST — evidence added, status unchanged. 19:36
- snac_and_water — for the archive two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly, your mileage will differ 19:49
- mcg_not_mg — unrelated but ms/ms sequencing is the only thing i would call identity. everything else is circumstantial 20:15
- VialBot — Archive lookup: HPLC_Hank first appears in this channel on 2025-11-01. 21:53
- monoisotopic — co-elution is the failure mode that a beautiful single peak is most likely to be hiding 22:43
update on the earlier thing how do you spot a deletion in a sequence from mass alone
baseline is drifting badly, is that the column or the mobile phase
Verification log updated: QST — evidence added, status unchanged.
for the archive two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly, your mileage will differ
plus 16 is oxidation
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for the archive is uv at 214 or 280 better for peptides
within inter-lab range
thats a charge state
the first peak is the solvent. it is always the solvent
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has anyone ever had a result where the mass was right and the purity was wrong
integration choices move the number by a few tenths easily. that is most of your inter-lab variance, ill dig out the number
coming back to this 214nm sees the amide backbone so it sees everything. 280 only sees aromatics
unrelated but ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
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genuine question truncations show as a mass deficit matching one or more residues. you need the sequence to say which
slightly off topic but retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily
ms/ms or it isnt identity
thats co-elution
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 substanceArchive lookup: HPLC_Hank first appears in this channel on 2025-11-01.
coming back to this a shoulder on a peak is information, and usually bad information
co-elution is the failure mode that a beautiful single peak is most likely to be hiding
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sorry to jump in tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5
shallow gradient
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shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly