deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
[edited]#hplc-massspec 2026-05-19
Tuesday22 messages5 participantstimes are UTC
Highlights from this day
- HPLC_Hank — can you tell a dimer from the chromatogram alone 16:50
- sulphur_burp — if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic 17:36
- LC_MS_Lena — a certificate with a number and no chromatogram is asking you to trust the integration you cannot see 18:25
do the arithmetic
can you tell a dimer from the chromatogram alone
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oxidation is about plus 15.99 Da and is usually methionine or tryptophan, i have it written down somewhere
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
update on the earlier thing two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly, anyway
genuine question the first peak is the solvent. it is always the solvent
214nm sees the amide backbone so it sees everything. 280 only sees aromatics
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has anyone ever had a result where the mass was right and the purity was wrong
retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily
i was wrong about tailing factor. it is usually the injection or the pH, not the column
i have a number at about a third of what i expected, is that a charge state
plus 16 is oxidation
is there any point running a blank if the sample is the question
if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
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*Medutest not the other one
a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
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retention time is a hint
show me the spectrum
need more sample
[edited]how would a truncation sequence show up
nobody runs enough blanks, including me
integration choices move the number by a few tenths easily. that is most of your inter-lab variance