semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
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#hplc-massspec 2025-09-26
Friday38 messages7 participantstimes are UTC
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follow up two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
can you tell a dimer from the chromatogram alone
within inter-lab range
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
relative retention time against a standard is comparable between labs. absolute minutes are not
while im here deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
right so whats the void volume peak, is that always solvent
plus sixteen, is that always oxidation
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integration choices move the number by a few tenths easily. that is most of your inter-lab variance
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coming back to this the first peak is the solvent. it is always the solvent
*VendorInvestigate not the other one
i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
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a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
how would a truncation sequence show up
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shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
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shame_and_medsa certificate with a number and no chromatogram is asking you to trust the integration…
right so 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
is a tailing factor of anything specific a problem
integration choices move the number by a few tenths easily. that is most of your inter-lab variance
peak RRT area% note
1 0.42 0.31 solvent front
2 0.88 0.44 related substance
3 1.00 98.72 main
4 1.14 0.53 related substancehas anyone ever had a result where the mass was right and the purity was wrong
update on the earlier thing is there any point running a blank if the sample is the question
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need more sample
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how much sample does a lab actually need for identity as well as purity
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does ms/ms actually prove identity or just make it very likely
does retention time on its own tell you what the compound is
plus 0.98 is deamidation
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thats co-elution
*that should say weekly
shallow gradient
transit-times.csv
112 rows · not retained in the public archive
if the lab reports area percent without stating the wavelength, the number is less useful than it looks
plus 16 is oxidation
truncations show as a mass deficit matching one or more residues. you need the sequence to say which
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how do you tell co-elution from a clean single peak
thats a charge state
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sorry to jump in retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily
whats a plus one dalton shift usually
a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
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integration difference