unrelated but i have a number at about a third of what i expected, is that a charge state
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 -> consistent#hplc-massspec 2025-07-27
Sunday35 messages9 participantstimes are UTC
Highlights from this day
- karl_fischer — unrelated but i have a number at about a third of what i expected, is that a charge state 16:30
- karl_fischer — a warm transit can put a visible degradant peak on a chromatogram. that is what 14 days at ambient does 17:13
- cold_chain_cmdr — semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2 18:26
- cold_chain_cmdr — whats a normal gradient for a peptide this size 20:05
retention time is a hint
run a blank
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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
within inter-lab range
a warm transit can put a visible degradant peak on a chromatogram. that is what 14 days at ambient does
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plus sixteen, is that always oxidation
truncations show as a mass deficit matching one or more residues. you need the sequence to say which
do the arithmetic
whats the void volume peak, is that always solvent
for the archive shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
*Janoshik not the other one
214nm sees the amide backbone so it sees everything. 280 only sees aromatics
need more sample
how much sample does a lab actually need for identity as well as purity
slightly off topic but is monoisotopic or average mass the one on most certificates
do you trust an area percent from a shallow gradient
baseline is drifting badly, is that the column or the mobile phase
tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5
semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
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integration difference
shallow gradient
is uv at 214 or 280 better for peptides
thats co-elution
thats the solvent peak
if the lab reports area percent without stating the wavelength, the number is less useful than it looks
deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
can you tell a dimer from the chromatogram alone
genuine question how do you tell co-elution from a clean single peak
Channel stats, last 30 days: 61 messages from 11 members.
show me the spectrum
whats a normal gradient for a peptide this size
weights-monthly.csv
532 rows · not retained in the public archive
the first peak is the solvent. it is always the solvent
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
thats a charge state
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plus 16 is oxidation
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