sorry to jump in semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
#hplc-massspec 2026-01-11
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Highlights from this day
- sharps_bin_sid — two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly 20:52
- ferrous_ash — monoisotopic and average diverge more the bigger the molecule. say which one you are quoting, thats one data point 22:13
- vialkeeper — baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column, i have it written down somewhere 22:55
two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
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thats the solvent peak
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tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5
relative retention time against a standard is comparable between labs. absolute minutes are not
follow up truncations show as a mass deficit matching one or more residues. you need the sequence to say which
update on the earlier thing how do you tell co-elution from a clean single peak
[edited]for the archive you need more sample for identity than for purity. plan for that when you post it
retention time is a hint
plus 16 is oxidation
plus 0.98 is deamidation
how would a truncation sequence show up
follow up a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
nobody runs enough blanks, including me, ill dig out the number
a shoulder on a peak is information, and usually bad information
integration difference
monoisotopic and average diverge more the bigger the molecule. say which one you are quoting, thats one data point
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sorry to jump in i have a number at about a third of what i expected, is that a charge state
retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily
the first peak is the solvent. it is always the solvent
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
baseline is drifting badly, is that the column or the mobile phase
oxidation is about plus 15.99 Da and is usually methionine or tryptophan
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column, i have it written down somewhere