semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
#hplc-massspec 2026-05-29
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do the arithmetic
the first peak is the solvent. it is always the solvent
shallow gradient
relative retention time against a standard is comparable between labs. absolute minutes are not
thats a charge state
can you tell a dimer from the chromatogram alone
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oxidation is about plus 15.99 Da and is usually methionine or tryptophan
unrelated but you need more sample for identity than for purity. plan for that when you post it
a warm transit can put a visible degradant peak on a chromatogram. that is what 17 days at ambient does, ymmv
i was wrong about tailing factor. it is usually the injection or the pH, not the column
deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
baseline is drifting badly, is that the column or the mobile phase
deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
co-elution is the failure mode that a beautiful single peak is most likely to be hiding
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thats co-elution
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plus 0.98 is deamidation
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how do you tell co-elution from a clean single peak
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how do you spot a deletion in a sequence from mass alone
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
monoisotopic and average diverge more the bigger the molecule. say which one you are quoting
plus 16 is oxidation
M = 4113.6
[M+2H]2+ = (4113.6 + 2.02) / 2 = 2057.8
[M+3H]3+ = (4113.6 + 3.02) / 3 = 1372.2
observed 1372.3 -> consistentrun a blank
a shoulder on a peak is information, and usually bad information
a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
Recon calculator: 30mg in 1.5ml = 8mg/ml.
within inter-lab range
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a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
integration choices move the number by a few tenths easily. that is most of your inter-lab variance