show me the spectrum
#hplc-massspec 2026-02-23
Monday31 messages6 participantstimes are UTC
Highlights from this day
- impersonator_ip — the honest position is that hobby-level interpretation of a chromatogram is worth something but not much 16:41
- impersonator_ip — i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer, take that with a pinch of salt 17:36
- salt_bridge — is there any point running a blank if the sample is the question 18:05
- impersonator_ip — plus sixteen, is that always oxidation 18:15
- deamidation — a warm transit can put a visible degradant peak on a chromatogram. that is what 12 days at ambient does 18:28
retention time is a hint
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is uv at 214 or 280 better for peptides
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a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
ask for the trace
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 -> consistentretention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
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✅4🧪7💀1
do the arithmetic
thats co-elution
ok so why do two labs integrate the same peak differently
how do you tell co-elution from a clean single peak
whats a normal gradient for a peptide this size
i have a number at about a third of what i expected, is that a charge state
does retention time on its own tell you what the compound is
i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer, take that with a pinch of salt
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you need more sample for identity than for purity. plan for that when you post it
within inter-lab range
is there any point running a blank if the sample is the question
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integration choices move the number by a few tenths easily. that is most of your inter-lab variance
a warm transit can put a visible degradant peak on a chromatogram. that is what 21 days at ambient does
plus sixteen, is that always oxidation
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a warm transit can put a visible degradant peak on a chromatogram. that is what 12 days at ambient does
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coming back after 8 months, what changed in how you read these
quick one monoisotopic and average diverge more the bigger the molecule. say which one you are quoting
my peak has a shoulder on it, what does that usually mean
coming back to this why does integration change the number so much
update on the earlier thing is monoisotopic or average mass the one on most certificates
plus 0.98 is deamidation
thats a charge state
update from 14 months ago: switched to asking for the chromatogram rather than the number and it changed everything
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 -> consistenthas anyone ever had a result where the mass was right and the purity was wrong