nobody runs enough blanks, including me
#hplc-massspec 2026-04-10
Friday26 messages6 participantstimes are UTC
Highlights from this day
- peak_split — why does integration change the number so much 02:06
- swirl_not_shake — monoisotopic and average diverge more the bigger the molecule. say which one you are quoting 02:09
- swirl_not_shake — a shoulder on a peak is information, and usually bad information 02:59
- deamidation — coming back after 3 months, what changed in how you read these you need more sample for identity than for purity. plan for that when you post it 03:38
- cold_pack_carla — integration choices move the number by a few tenths easily. that is most of your inter-lab variance 04:09
the first peak is the solvent. it is always the solvent
has anyone ever had a result where the mass was right and the purity was wrong
i have a number at about a third of what i expected, is that a charge state
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
ms/ms or it isnt identity
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plus sixteen, is that always oxidation
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
show me the spectrum
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why does integration change the number so much
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monoisotopic and average diverge more the bigger the molecule. say which one you are quoting
M = 4113.6
[M+2H]2+ = (4113.6 + 2.02) / 2 = 2057.8
[M+3H]3+ = (4113.6 + 3.02) / 3 = 1372.2
observed 1372.3 -> consistentask for the trace
plus 16 is oxidation
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sorry to jump in baseline is drifting badly, is that the column or the mobile phase
is a tailing factor of anything specific a problem
retention time is a hint
a shoulder on a peak is information, and usually bad information
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my peak has a shoulder on it, what does that usually mean
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coming back after 3 months, what changed in how you read these
you need more sample for identity than for purity. plan for that when you post it
relative retention time against a standard is comparable between labs. absolute minutes are not, someone check my working
integration difference
i was wrong about tailing factor. it is usually the injection or the pH, not the column, still working it out
integration choices move the number by a few tenths easily. that is most of your inter-lab variance
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shallow gradient
how much sample does a lab actually need for identity as well as purity