genuine question i was wrong about tailing factor. it is usually the injection or the pH, not the column
#hplc-massspec 2025-08-02
Saturday36 messages8 participantstimes are UTC
Highlights from this day
- fibre_first — co-elution is the failure mode that a beautiful single peak is most likely to be hiding 16:50
- void_volume — how do you tell co-elution from a clean single peak 16:53
- HPLC_Hank — if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result, ill dig out the number 17:35
- VialBot — Verification log updated: Homopeptide — evidence added, status unchanged. 18:30
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
co-elution is the failure mode that a beautiful single peak is most likely to be hiding
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integration choices move the number by a few tenths easily. that is most of your inter-lab variance
how do you tell co-elution from a clean single peak
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relative retention time against a standard is comparable between labs. absolute minutes are not, n of 1 obviously
i have a number at about a third of what i expected, is that a charge state
oxidation is about plus 15.99 Da and is usually methionine or tryptophan
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result, ill dig out the number
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the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
is monoisotopic or average mass the one on most certificates
i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
Verification log updated: Homopeptide — evidence added, status unchanged.
ms/ms or it isnt identity
need more sample
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Verification log updated: QST — evidence added, status unchanged.
shallow gradient
within inter-lab range
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the first peak is the solvent. it is always the solvent
whats a normal gradient for a peptide this size
is there any point running a blank if the sample is the question
ok so monoisotopic and average diverge more the bigger the molecule. say which one you are quoting
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plus 0.98 is deamidation
a shoulder on a peak is information, and usually bad information
fridge-temps.csv
671 rows · not retained in the public archive
run a blank
how do you spot a deletion in a sequence from mass alone
ask for the trace
sorry to jump in if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
[edited]can you tell a dimer from the chromatogram alone
do you trust an area percent from a shallow gradient
nobody runs enough blanks, including me
does ms/ms actually prove identity or just make it very likely
214nm sees the amide backbone so it sees everything. 280 only sees aromatics
baseline is drifting badly, is that the column or the mobile phase
thats the solvent peak
slightly off topic but my peak has a shoulder on it, what does that usually mean