relative retention time against a standard is comparable between labs. absolute minutes are not
#hplc-massspec 2026-03-29
Sunday26 messages7 participantstimes are UTC
Highlights from this day
- adelaide_assay — how do you tell co-elution from a clean single peak 12:54
- patent_2026 — if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result 15:57
- adelaide_assay — quick one the honest position is that hobby-level interpretation of a chromatogram is worth something but not much 16:02
within inter-lab range
truncations show as a mass deficit matching one or more residues. you need the sequence to say which
ok so nobody runs enough blanks, including me
📈2❤️8
how do you tell co-elution from a clean single peak
⚠️15😂6
a shoulder on a peak is information, and usually bad information
a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
😂1
how would a truncation sequence show up
tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
a shoulder on a peak is information, and usually bad information
Batch lookup A-2418: 4 independent reports on file, earliest 2025-07-24.
how much sample does a lab actually need for identity as well as purity
show me the spectrum
❤️1
co-elution is the failure mode that a beautiful single peak is most likely to be hiding, anyway
you need more sample for identity than for purity. plan for that when you post it
Inter-lab diff for lot G-0641: 98.1% vs 99.4%. Within expected range.
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
✅12🎉7
is uv at 214 or 280 better for peptides
[edited]quick one the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
🙏4⚠️12🧊4
shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
do the arithmetic
ask for the trace
ms/ms or it isnt identity
📈2
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
💀4
shallow gradient
genuine question my peak has a shoulder on it, what does that usually mean