Archive lookup: font_forensics first appears in this channel on 2025-01-13.
#hplc-massspec 2025-03-21
Friday31 messages9 participantstimes are UTC
Highlights from this day
- font_forensics — monoisotopic and average diverge more the bigger the molecule. say which one you are quoting 11:17
- font_forensics — deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant 11:18
- forty_units — sorry to jump in truncations show as a mass deficit matching one or more residues. you need the sequence to say which 11:42
- forty_units — the honest position is that hobby-level interpretation of a chromatogram is worth something but not much, happy to be corrected 13:33
monoisotopic and average diverge more the bigger the molecule. say which one you are quoting
medutest-report-f-1330.pdf
3 pages · 152 KB · not retained in the public archive
deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
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tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5
if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
has anyone ever had a result where the mass was right and the purity was wrong
nobody runs enough blanks, including me
if the lab reports area percent without stating the wavelength, the number is less useful than it looks
whats a normal gradient for a peptide this size
whats a plus one dalton shift usually
how do you spot a deletion in a sequence from mass alone
integration choices move the number by a few tenths easily. that is most of your inter-lab variance
why do two labs integrate the same peak differently
sorry to jump in truncations show as a mass deficit matching one or more residues. you need the sequence to say which
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Reminder set. I will post here in 3 days.
the first peak is the solvent. it is always the solvent
[edited]my peak has a shoulder on it, what does that usually mean
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how much sample does a lab actually need for identity as well as purity
i was wrong about tailing factor. it is usually the injection or the pH, not the column
thats the solvent peak
you need more sample for identity than for purity. plan for that when you post it
shallow gradient
a warm transit can put a visible degradant peak on a chromatogram. that is what 6 days at ambient does
a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
coming back to this a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
thats a charge state
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i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
update from 23 months ago: switched to asking for the chromatogram rather than the number and it changed everything
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial, ask me again in a month
update on the earlier thing i asked VendorInvestigate for the raw trace and they sent it. that is the right answer to that question
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much, happy to be corrected
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