shallow gradient
#hplc-massspec 2025-11-24
Monday35 messages9 participantstimes are UTC
Highlights from this day
- ms_ms_mira — if the lab reports area percent without stating the wavelength, the number is less useful than it looks 09:53
- VialBot — Archive lookup: area_percent first appears in this channel on 2025-02-27. 14:19
- HPLC_Hank — the honest position is that hobby-level interpretation of a chromatogram is worth something but not much, your mileage will differ a warm transit can put a visible… 16:10
if the lab reports area percent without stating the wavelength, the number is less useful than it looks
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is there any point running a blank if the sample is the question
run a blank
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a warm transit can put a visible degradant peak on a chromatogram. that is what 20 days at ambient does
*that should say weekly
relative retention time against a standard is comparable between labs. absolute minutes are not
integration difference
[edited]Batch lookup A-2601: 9 independent reports on file, earliest 2025-04-07.
do the arithmetic
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integration choices move the number by a few tenths easily. that is most of your inter-lab variance
plus sixteen, is that always oxidation
within inter-lab range
truncations show as a mass deficit matching one or more residues. you need the sequence to say which
update from 15 months ago: switched to asking for the chromatogram rather than the number and it changed everything
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
monoisotopic and average diverge more the bigger the molecule. say which one you are quoting
has anyone ever had a result where the mass was right and the purity was wrong
you need more sample for identity than for purity. plan for that when you post it, ill dig out the number
ask for the trace
how would a truncation sequence show up
do you trust an area percent from a shallow gradient
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
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
Archive lookup: area_percent first appears in this channel on 2025-02-27.
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ok so is a tailing factor of anything specific a problem
plus 0.98 is deamidation
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much, your mileage will differ
a warm transit can put a visible degradant peak on a chromatogram. that is what 23 days at ambient does
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i asked Medutest for the raw trace and they sent it. that is the right answer to that question
whats a normal gradient for a peptide this size
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whats a plus one dalton shift usually
thats co-elution
why does integration change the number so much
co-elution is the failure mode that a beautiful single peak is most likely to be hiding