deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
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#hplc-massspec 2025-10-23
Thursday42 messages11 participantstimes are UTC
Highlights from this day
- two_four_ceiling — if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result 17:34
- two_four_ceiling — how much sample does a lab actually need for identity as well as purity 18:36
- peak_split — semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2 19:54
i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
plus 16 is oxidation
shallow gradient
need more sample
[edited]i have a number at about a third of what i expected, is that a charge state
[edited]update on the earlier thing can you tell a dimer from the chromatogram alone
the first peak is the solvent. it is always the solvent
Recon calculator: 2mg in 2ml = 5mg/ml.
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
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sorry to jump in how would a truncation sequence show up
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retention time is a hint
coming back after 2 months, what changed in how you read these
thats the solvent peak
Purity check: no report on file for lot B-0329. Nothing logged either way.
integration difference
thats a charge state
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does ms/ms actually prove identity or just make it very likely
tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5
how much sample does a lab actually need for identity as well as purity
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is a tailing factor of anything specific a problem
if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
show me the spectrum
baseline is drifting badly, is that the column or the mobile phase
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thats co-elution
plus 0.98 is deamidation
within inter-lab range
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column, ask me again in a month
oxidation is about plus 15.99 Da and is usually methionine or tryptophan
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ask for the trace
On this day 8 years ago this channel logged 135 messages.
run a blank
the first peak is the solvent. it is always the solvent, your mileage will differ
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semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
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if the lab reports area percent without stating the wavelength, the number is less useful than it looks
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do you trust an area percent from a shallow gradient
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
you need more sample for identity than for purity. plan for that when you post it
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co-elution is the failure mode that a beautiful single peak is most likely to be hiding, happy to be corrected
shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
i asked Janoshik for the raw trace and they sent it. that is the right answer to that question
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nobody runs enough blanks, including me
is monoisotopic or average mass the one on most certificates