need more sample
#hplc-massspec 2025-04-15
Tuesday36 messages7 participantstimes are UTC
Highlights from this day
- tail_factor — baseline is drifting badly, is that the column or the mobile phase 21:24
- deamidation — if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic 21:48
- relabel_watch — retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily, n of 1 obviously 22:25
- relabel_watch — for the archive can you tell a dimer from the chromatogram alone 22:29
retention time is a hint
tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5
[edited]plus 0.98 is deamidation
how do you tell co-elution from a clean single peak
plus 16 is oxidation
is a tailing factor of anything specific a problem
coming back after 17 months, what changed in how you read these
within inter-lab range
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show me the spectrum
shallow gradient
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
baseline is drifting badly, is that the column or the mobile phase
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thats a charge state
thats the solvent peak
whats the void volume peak, is that always solvent
i was wrong about tailing factor. it is usually the injection or the pH, not the column
[edited]my peak has a shoulder on it, what does that usually mean
has anyone ever had a result where the mass was right and the purity was wrong
does retention time on its own tell you what the compound is
a warm transit can put a visible degradant peak on a chromatogram. that is what 13 days at ambient does
two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
how do you spot a deletion in a sequence from mass alone
how much sample does a lab actually need for identity as well as purity
the first peak is the solvent. it is always the solvent
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily, n of 1 obviously
integration difference
for the archive can you tell a dimer from the chromatogram alone
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why do two labs integrate the same peak differently
is monoisotopic or average mass the one on most certificates
thats co-elution
integration choices move the number by a few tenths easily. that is most of your inter-lab variance
if the lab reports area percent without stating the wavelength, the number is less useful than it looks
you need more sample for identity than for purity. plan for that when you post it, still working it out