why does integration change the number so much
#hplc-massspec 2025-03-04
Tuesday30 messages9 participantstimes are UTC
Highlights from this day
- brisbane_bac — genuine question nobody runs enough blanks, including me 21:49
- blank_run — genuine question is monoisotopic or average mass the one on most certificates 21:58
- taper_tess — how much sample does a lab actually need for identity as well as purity 22:30
- cagri_curious — if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result 22:31
- acetate_ash — a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you 22:55
genuine question nobody runs enough blanks, including me
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whats a normal gradient for a peptide this size
ms/ms or it isnt identity
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genuine question is monoisotopic or average mass the one on most certificates
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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
has anyone ever had a result where the mass was right and the purity was wrong
i asked Medutest for the raw trace and they sent it. that is the right answer to that question
relative retention time against a standard is comparable between labs. absolute minutes are not
a shoulder on a peak is information, and usually bad information
does retention time on its own tell you what the compound is
plus 0.98 is deamidation
plus sixteen, is that always oxidation
how much sample does a lab actually need for identity as well as purity
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if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
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if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
thats a charge state
does ms/ms actually prove identity or just make it very likely
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
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oxidation is about plus 15.99 Da and is usually methionine or tryptophan
whats a plus one dalton shift usually
baseline is drifting badly, is that the column or the mobile phase
[edited]a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
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you need more sample for identity than for purity. plan for that when you post it
shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly, anyway
Archive lookup: truncation_tru first appears in this channel on 2024-12-20.
the first peak is the solvent. it is always the solvent
*Janoshik not the other one
how do you spot a deletion in a sequence from mass alone