thats a charge state
#hplc-massspec 2025-06-05
Thursday37 messages6 participantstimes are UTC
Highlights from this day
- quiet.hours — i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer 21:55
- maintenance_mo — a shoulder on a peak is information, and usually bad information 21:58
- identity_shift — whats a normal gradient for a peptide this size 22:54
- provincial_pat — you need more sample for identity than for purity. plan for that when you post it 22:57
- identity_shift — i asked PeptideMeter for the raw trace and they sent it. that is the right answer to that question 23:06
how do you spot a deletion in a sequence from mass alone
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 shoulder on a peak is information, and usually bad information
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how much sample does a lab actually need for identity as well as purity
is a tailing factor of anything specific a problem
unrelated but 214nm sees the amide backbone so it sees everything. 280 only sees aromatics, ask me again in a month
sorry to jump in do you trust an area percent from a shallow gradient
nobody runs enough blanks, including me
whats the void volume peak, is that always solvent
co-elution is the failure mode that a beautiful single peak is most likely to be hiding, thats just me
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
ask for the trace
a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
[edited]i was wrong about tailing factor. it is usually the injection or the pH, not the column
my peak has a shoulder on it, what does that usually mean
thats co-elution
thats the solvent peak
plus 0.98 is deamidation
is monoisotopic or average mass the one on most certificates
while im here relative retention time against a standard is comparable between labs. absolute minutes are not
semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
slightly off topic but oxidation is about plus 15.99 Da and is usually methionine or tryptophan
how would a truncation sequence show up
for the archive 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 12 days at ambient does
whats a normal gradient for a peptide this size
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you need more sample for identity than for purity. plan for that when you post it
lot-log.csv
276 rows · not retained in the public archive
deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
chromatogram-overlay.png
1240 × 720 · 685 KB · not retained in the public archive
i asked PeptideMeter for the raw trace and they sent it. that is the right answer to that question
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ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
why do two labs integrate the same peak differently
deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
how do you tell co-elution from a clean single peak
[edited]plus sixteen, is that always oxidation
integration choices move the number by a few tenths easily. that is most of your inter-lab variance
retention time is a hint
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coming back after 19 months, what changed in how you read these