monoisotopic and average diverge more the bigger the molecule. say which one you are quoting
#hplc-massspec 2025-11-15
Saturday25 messages7 participantstimes are UTC
Highlights from this day
- vik_verifies — slightly off topic but how much sample does a lab actually need for identity as well as purity 11:36
- vik_verifies — whats a normal gradient for a peptide this size co-elution is the failure mode that a beautiful single peak is most likely to be hiding 12:23
- area_percent — a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you 14:13
for the archive shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
Reminder set. I will post here in 7 days.
tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5
slightly off topic but how much sample does a lab actually need for identity as well as purity
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oxidation is about plus 15.99 Da and is usually methionine or tryptophan
quick one do you trust an area percent from a shallow gradient
is uv at 214 or 280 better for peptides
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
plus sixteen, is that always oxidation
whats a normal gradient for a peptide this size
co-elution is the failure mode that a beautiful single peak is most likely to be hiding
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co-elution is the failure mode that a beautiful single peak is most likely to be hiding
Batch lookup H-2814: 7 independent reports on file, earliest 2025-09-15.
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two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
the first peak is the solvent. it is always the solvent
is monoisotopic or average mass the one on most certificates
shallow gradient
a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
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can you tell a dimer from the chromatogram alone
semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2, happy to be corrected
a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
[edited]how do you spot a deletion in a sequence from mass alone
genuine question why does integration change the number so much
deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
plus 0.98 is deamidation