i was wrong about tailing factor. it is usually the injection or the pH, not the column
#hplc-massspec 2025-02-09
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thats co-elution
semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
[edited]how do you tell co-elution from a clean single peak
truncations show as a mass deficit matching one or more residues. you need the sequence to say which
retention time is a hint
retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily
ask for the trace
214nm sees the amide backbone so it sees everything. 280 only sees aromatics
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deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
how much sample does a lab actually need for identity as well as purity
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two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
a warm transit can put a visible degradant peak on a chromatogram. that is what 22 days at ambient does
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the first peak is the solvent. it is always the solvent
if the lab reports area percent without stating the wavelength, the number is less useful than it looks
Reminder set. I will post here in 6 days.
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need more sample
plus 0.98 is deamidation
nobody runs enough blanks, including me
thats a charge state
[edited]can you tell a dimer from the chromatogram alone
oxidation is about plus 15.99 Da and is usually methionine or tryptophan
does retention time on its own tell you what the compound is
follow up a shoulder on a peak is information, and usually bad information
ok so why do two labs integrate the same peak differently
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
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 substance