ms/ms or it isnt identity
#hplc-massspec 2025-11-19
Wednesday27 messages7 participantstimes are UTC
Highlights from this day
- VialBot — Testing queue: 3 submissions open, 97 awaiting dispatch. 08:47
- area_percent — i was wrong about tailing factor. it is usually the injection or the pH, not the column 10:42
- VialBot — Reminder set. I will post here in 6 days. 11:59
- relabel_watch — ok so a shoulder on a peak is information, and usually bad information, take that with a pinch of salt 12:27
Testing queue: 3 submissions open, 97 awaiting dispatch.
does retention time on its own tell you what the compound is
a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
do you trust an area percent from a shallow gradient
retention time is a hint
thats a charge state
plus 0.98 is deamidation
whats a plus one dalton shift usually
i was wrong about tailing factor. it is usually the injection or the pH, not the column
coa-kp-0925.pdf
1 page · 381 KB · not retained in the public archive
coming back after 17 months, what changed in how you read these
Reminder set. I will post here in 6 days.
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
co-elution is the failure mode that a beautiful single peak is most likely to be hiding
update from 17 months ago: switched to asking for the chromatogram rather than the number and it changed everything
ok so a shoulder on a peak is information, and usually bad information, take that with a pinch of salt
💀12
genuine question i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
plus 16 is oxidation
why do two labs integrate the same peak differently
[edited]show me the spectrum
fridge-temps.csv
99 rows · not retained in the public archive
does ms/ms actually prove identity or just make it very likely
deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant, happy to be corrected
shallow gradient
[edited]do the arithmetic
shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic