a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
#hplc-massspec 2025-06-19
Thursday29 messages7 participantstimes are UTC
Highlights from this day
- VialBot — New independent result logged — SGN, lot F-1330, purity 99.2% (VendorInvestigate). 19:13
- truncation_tru — is a tailing factor of anything specific a problem 19:48
- truncation_tru — oxidation is about plus 15.99 Da and is usually methionine or tryptophan truncations show as a mass deficit matching one or more residues. you need the sequence to… 19:52
- blank_run — how much sample does a lab actually need for identity as well as purity 20:06
- blank_run — 214nm sees the amide backbone so it sees everything. 280 only sees aromatics, i could be wrong 20:08
i have a number at about a third of what i expected, is that a charge state
if the lab reports area percent without stating the wavelength, the number is less useful than it looks
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column, from memory
while im here semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2, still working it out
run a blank
for the archive deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
show me the spectrum
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relative retention time against a standard is comparable between labs. absolute minutes are not
i asked Medutest for the raw trace and they sent it. that is the right answer to that question
New independent result logged — SGN, lot F-1330, purity 99.2% (VendorInvestigate).
thats the solvent peak
thats co-elution
peptidemeter-summary-f-1330.pdf
2 pages · 518 KB · not retained in the public archive
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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, someone check my working
is a tailing factor of anything specific a problem
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integration choices move the number by a few tenths easily. that is most of your inter-lab variance
oxidation is about plus 15.99 Da and is usually methionine or tryptophan
truncations show as a mass deficit matching one or more residues. you need the sequence to say which
if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
how much sample does a lab actually need for identity as well as purity
site-rotation-map.png
1000 × 700 · 133 KB · not retained in the public archive
need more sample
214nm sees the amide backbone so it sees everything. 280 only sees aromatics, i could be wrong
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has anyone ever had a result where the mass was right and the purity was wrong
why does integration change the number so much
tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5
how do you tell co-elution from a clean single peak
plus 16 is oxidation
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genuine question can you tell a dimer from the chromatogram alone
two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
retention time is a hint