plus 16 is oxidation
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#hplc-massspec 2025-09-24
Wednesday25 messages4 participantstimes are UTC
Highlights from this day
- area_percent — deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant 19:49
- area_percent — co-elution is the failure mode that a beautiful single peak is most likely to be hiding 20:01
- gip_glp_gil — if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result if the number you are staring at is a third of what you… 20:37
- seoul_swirl — 214nm sees the amide backbone so it sees everything. 280 only sees aromatics if the number you are staring at is a third of what you expected, do the charge state… 20:53
- pinch_not_stretch — semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2, from memory 22:35
deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
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a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
need more sample
co-elution is the failure mode that a beautiful single peak is most likely to be hiding
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i asked Medutest for the raw trace and they sent it. that is the right answer to that question
integration choices move the number by a few tenths easily. that is most of your inter-lab variance
shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly, your mileage will differ
thats a charge state
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retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily
is uv at 214 or 280 better for peptides
nobody runs enough blanks, including me
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
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baseline is drifting badly, is that the column or the mobile phase
monoisotopic and average diverge more the bigger the molecule. say which one you are quoting
214nm sees the amide backbone so it sees everything. 280 only sees aromatics
if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
truncations show as a mass deficit matching one or more residues. you need the sequence to say which
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
unrelated but a warm transit can put a visible degradant peak on a chromatogram. that is what 23 days at ambient does
why do two labs integrate the same peak differently
how do you spot a deletion in a sequence from mass alone
coming back to this a shoulder on a peak is information, and usually bad information
does retention time on its own tell you what the compound is
semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2, from memory
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you need more sample for identity than for purity. plan for that when you post it