coming back after 18 months, what changed in how you read these
#hplc-massspec 2025-01-29
Wednesday33 messages5 participantstimes are UTC
Highlights from this day
- pbs_pip — deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant 22:11
- void_volume — plus sixteen, is that always oxidation 22:26
- pbs_pip — whats a normal gradient for a peptide this size 22:41
- pbs_pip — baseline is drifting badly, is that the column or the mobile phase 22:44
- pbs_pip — whats a plus one dalton shift usually 23:02
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
thats a charge state
is monoisotopic or average mass the one on most certificates
deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
site-rotation-map.png
1000 × 700 · 835 KB · not retained in the public archive
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
can you tell a dimer from the chromatogram alone
i was wrong about tailing factor. it is usually the injection or the pH, not the column
whats the void volume peak, is that always solvent
plus sixteen, is that always oxidation
🙏15🧊3⚠️2
shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
how much sample does a lab actually need for identity as well as purity
thats the solvent peak
plus 0.98 is deamidation
peak RRT area% note
1 0.42 0.31 solvent front
2 0.88 0.44 related substance
3 1.00 98.72 main
4 1.14 0.53 related substancewhats a normal gradient for a peptide this size
🎉17🧊2🧪5
baseline is drifting badly, is that the column or the mobile phase
📈2🔥1🧊10
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
has anyone ever had a result where the mass was right and the purity was wrong
ms/ms or it isnt identity
is uv at 214 or 280 better for peptides
whats a plus one dalton shift usually
📉10⚠️5💀4
does ms/ms actually prove identity or just make it very likely
do you trust an area percent from a shallow gradient
do the arithmetic
within inter-lab range
i have a number at about a third of what i expected, is that a charge state
integration difference
ask for the trace
update on the earlier thing a shoulder on a peak is information, and usually bad information
quick one is a tailing factor of anything specific a problem
show me the spectrum