need more sample
#hplc-massspec 2025-03-29
Saturday30 messages6 participantstimes are UTC
Highlights from this day
- apnoea_down_two — follow up does retention time on its own tell you what the compound is 14:44
- baseline_drift — is there any point running a blank if the sample is the question 15:08
- void_volume — do you trust an area percent from a shallow gradient deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant 15:10
- factory_direct_fi — the first peak is the solvent. it is always the solvent, thats one data point 16:09
- void_volume — whats a normal gradient for a peptide this size 16:22
coming back to this i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
13:41chlorhex pinned a message
two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
ms/ms or it isnt identity
can you tell a dimer from the chromatogram alone
coming back after 15 months, what changed in how you read these
*Janoshik not the other one
you need more sample for identity than for purity. plan for that when you post it
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
follow up does retention time on its own tell you what the compound is
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monoisotopic and average diverge more the bigger the molecule. say which one you are quoting
thats a charge state
shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
how do you spot a deletion in a sequence from mass alone
is uv at 214 or 280 better for peptides
for the archive update from 14 months ago: switched to asking for the chromatogram rather than the number and it changed everything
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
is a tailing factor of anything specific a problem
is there any point running a blank if the sample is the question
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do you trust an area percent from a shallow gradient
deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
i have a number at about a third of what i expected, is that a charge state
i asked PeptideMeter for the raw trace and they sent it. that is the right answer to that question
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
ask for the trace
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 substancethe first peak is the solvent. it is always the solvent, thats one data point
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a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
integration difference
whats a normal gradient for a peptide this size
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thats co-elution