truncations show as a mass deficit matching one or more residues. you need the sequence to say which
#hplc-massspec 2026-06-27
Saturday38 messages7 participantstimes are UTC
Highlights from this day
- charge_state — unrelated but retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily monoisotopic and average diverge more the bigger the… 17:31
- VialBot — Recon calculator: 15mg in 2.5ml = 2mg/ml. 19:19
- no_chargeback — unrelated but do you trust an area percent from a shallow gradient 19:23
- shame_and_meds — whats a normal gradient for a peptide this size 20:17
- ms_ms_mira — coming back after 4 months, what changed in how you read these 23:03
i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
unrelated but retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily
monoisotopic and average diverge more the bigger the molecule. say which one you are quoting
integration difference
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plus sixteen, is that always oxidation
co-elution is the failure mode that a beautiful single peak is most likely to be hiding
i asked PeptideMeter for the raw trace and they sent it. that is the right answer to that question
[edited]*that should say weekly
how would a truncation sequence show up
while im here if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
retention time is a hint
a warm transit can put a visible degradant peak on a chromatogram. that is what 18 days at ambient does
baseline is drifting badly, is that the column or the mobile phase
deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
quick one is uv at 214 or 280 better for peptides
quick one two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
update from 6 months ago: switched to asking for the chromatogram rather than the number and it changed everything
the first peak is the solvent. it is always the solvent, not advice obviously
has anyone ever had a result where the mass was right and the purity was wrong
a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
Recon calculator: 15mg in 2.5ml = 2mg/ml.
within inter-lab range
unrelated but do you trust an area percent from a shallow gradient
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need more sample
ms/ms or it isnt identity
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relative retention time against a standard is comparable between labs. absolute minutes are not
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
shallow gradient
whats a normal gradient for a peptide this size
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how much sample does a lab actually need for identity as well as purity
monoisotopic and average diverge more the bigger the molecule. say which one you are quoting
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nobody runs enough blanks, including me
run a blank
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how do you tell co-elution from a clean single peak
thats the solvent peak
unrelated but semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2, thats one data point
coming back after 4 months, what changed in how you read these
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