can you tell a dimer from the chromatogram alone
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#hplc-massspec 2025-04-12
Saturday22 messages4 participantstimes are UTC
Highlights from this day
- vialkeeper — can you tell a dimer from the chromatogram alone 17:01
- pin29g — genuine question has anyone ever had a result where the mass was right and the purity was wrong if somebody says they ran a mass spec and does not show you a… 17:31
- typosquat_tay — nobody runs enough blanks, including me 17:32
- typosquat_tay — how do you tell co-elution from a clean single peak 17:49
- vialkeeper — does retention time on its own tell you what the compound is 19:23
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
show me the spectrum
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is a tailing factor of anything specific a problem
truncations show as a mass deficit matching one or more residues. you need the sequence to say which
genuine question has anyone ever had a result where the mass was right and the purity was wrong
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
nobody runs enough blanks, including me
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right so i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
whats a normal gradient for a peptide this size
tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5, still working it out
slightly off topic but if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
how do you tell co-elution from a clean single peak
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do the arithmetic
i have a number at about a third of what i expected, is that a charge state
the first peak is the solvent. it is always the solvent, from memory
ask for the trace
oxidation is about plus 15.99 Da and is usually methionine or tryptophan
ok so monoisotopic and average diverge more the bigger the molecule. say which one you are quoting
does retention time on its own tell you what the compound is
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thats a charge state
[edited]run a blank
M = 4113.6
[M+2H]2+ = (4113.6 + 2.02) / 2 = 2057.8
[M+3H]3+ = (4113.6 + 3.02) / 3 = 1372.2
observed 1372.3 -> consistenthow would a truncation sequence show up