retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily
#hplc-massspec 2026-04-15
Wednesday24 messages6 participantstimes are UTC
Highlights from this day
- lyophile_liv — update on the earlier thing how much sample does a lab actually need for identity as well as purity 21:40
- alt_ast_ali — slightly off topic but if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic 21:44
- salt_bridge — tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5, your mileage will differ 21:53
- forty_five_kg — if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result a shoulder on a peak is information, and usually bad information 23:08
relative retention time against a standard is comparable between labs. absolute minutes are not, i think
integration difference
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update on the earlier thing how much sample does a lab actually need for identity as well as purity
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*VendorInvestigate not the other one
slightly off topic but if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
while im here i was wrong about tailing factor. it is usually the injection or the pH, not the column
tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5, your mileage will differ
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thats a charge state
ms/ms or it isnt identity
ask for the trace
plus 16 is oxidation
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a warm transit can put a visible degradant peak on a chromatogram. that is what 26 days at ambient does
oxidation is about plus 15.99 Da and is usually methionine or tryptophan
i asked PeptideMeter for the raw trace and they sent it. that is the right answer to that question
shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly, n of 1 obviously
can you tell a dimer from the chromatogram alone
show me the spectrum
need more sample
does ms/ms actually prove identity or just make it very likely
[edited]baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
how do you tell co-elution from a clean single peak
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
a shoulder on a peak is information, and usually bad information
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much