thats co-elution
#hplc-massspec 2026-03-14
Saturday30 messages7 participantstimes are UTC
Highlights from this day
- protein_floor — update from 1 months ago: switched to asking for the chromatogram rather than the number and it changed everything 16:54
- protein_floor — does retention time on its own tell you what the compound is 16:55
- protein_floor — i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer 16:57
- VialBot — Inter-lab diff for lot C-4402: 96.8% vs 98.6%. Within expected range. 18:57
- per_mg_pete — semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2 retention time is a hint, not a fingerprint. two different peptides can co-elute… 20:00
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
within inter-lab range
📉16
ask for the trace
🔥13😂14📉8
*PeptideMeter not the other one
update on the earlier thing baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
the first peak is the solvent. it is always the solvent
need more sample
214nm sees the amide backbone so it sees everything. 280 only sees aromatics
integration difference
📈2
update from 1 months ago: switched to asking for the chromatogram rather than the number and it changed everything
📈12✅1
does retention time on its own tell you what the compound is
i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
[edited]👀16📉9⚠️6
whats the void volume peak, is that always solvent
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
💀1
a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
*PeptideMeter not the other one
thats a charge state
if the lab reports area percent without stating the wavelength, the number is less useful than it looks, take that with a pinch of salt
how do you tell co-elution from a clean single peak
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial, thats just me
i asked PeptideMeter for the raw trace and they sent it. that is the right answer to that question
for the archive truncations show as a mass deficit matching one or more residues. you need the sequence to say which
unrelated but deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
slightly off topic but is there any point running a blank if the sample is the question
why does integration change the number so much
Inter-lab diff for lot C-4402: 96.8% vs 98.6%. Within expected range.
👀1
can you tell a dimer from the chromatogram alone
semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily
retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily, not advice obviously