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[Lab] LC-MS confirmed identity but the UV purity is 94%. now what
Research peptide, not a GLP-1, from a vendor I will not name because this is a methodology question rather than a vendor post. MS confirms the expected molecular mass…
u/mass_spec_maggie
LC-MS/MS is my day job. Peptide mapping is my hobby. Both are the same job.
long-standing contributor · MS · joined 19 Jan 2024
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comment on why is the sequence written four different ways across four vendor sites in c/researchpeptides · 121 points · 1 days ago
and if they send a mass that does not match the sequence they sent, you have learned something enormous for the price of one email.
comment on two labs, same vial, 98.1 and 96.4. both right? in c/hplc · 176 points · 2 days ago
and none of the four items on that list touch identity. all of them are arguments about how much of what the detector saw was the main species. whether the main species is the right molecule is a different instrument.
comment on peak at 4.2 min, nobody can tell me what it is, ideas in c/hplc · 88 points · 3 days ago
send me a vial and i will run it on a lunch break. genuinely. modmail.
comment on peak at 4.2 min, nobody can tell me what it is, ideas in c/hplc · 104 points · 3 days ago
the general answer to "what is this peak" is always MS. UV gives you a retention time and a size, which narrows it to a family.
comment on [Lab] LC-MS confirmed identity but the UV purity is 94%. now what in c/hplc · 118 points · 3 days ago
so the practical read is: correct molecule, honest vendor, old vial. that is a much more actionable conclusion than "94% bad".
comment on bought a second-hand HPLC. worst best decision of my life. AMA in c/hplc · 96 points · 3 days ago
next purchase should be a used single-quad if you can find one. identity is the question UV cannot answer and you are one instrument away from answering it.
comment on [Lab] LC-MS confirmed identity but the UV purity is 94%. now what in c/hplc · 108 points · 3 days ago
a 94% that is one identified oxidation product on an old vial and a 94% that is six unknown peaks are not the same material. that is not avoidance, it is the actual difference.
comment on [Lab] LC-MS confirmed identity but the UV purity is 94%. now what in c/hplc · 187 points · 3 days ago
i can and i should have. edit next day: it is +16 on the parent mass. so an oxidation product, almost certainly methionine, and almost certainly a storage or handling artefact rather than a synthesis failure.
comment on [Method] the gradient everyone uses for sema and why it under-resolves the des-amido in c/hplc · 15 points · 3 days ago
state the method: column, gradient, detection wavelength, injection volume
comment on [PSA] severe abdominal pain is not a forum question in c/sideeffects · 21 points · 4 days ago
week 31 and the early fullness is finally getting better
Yes, exactly this, and it is the bit that took me 84 weeks to accept.
comment on [Log] public log, started week 1, currently week 90, still updating in c/dosinglogs · 3 points · 5 days ago
the boring consistency is the point
comment on peak at 4.2 min, nobody can tell me what it is, ideas in c/hplc · 11 points · 5 days ago
Removed a chain here. The rule is one line long and it is not negotiable.
comment on [Correction] you cannot report area% to two decimals off that baseline in c/hplc · 7 points · 6 days ago
This is an urgent-care question wearing a forum question's clothes. Please contact a clinician rather than waiting for replies.
comment on [Explainer] integration decisions change your number more than the sample does in c/hplc · 28 points · 8 days ago
What was the column and what gradient?
comment on reflux got worse for three weeks then better than baseline in c/sideeffects · 105 points · 9 days ago
I am going to push back on this slightly.
comment on [Method] 220nm vs 214nm and what you lose at each in c/hplc · 1 points · 12 days ago
Retitled to remove editorialising. Put the evidence in the body.
comment on [Regain] 4kg back over a year and i am calling that a win in c/maintenancephase · 11 points · 15 days ago
Maintenance for 11 months now. 7.5mg every 10 days, weight 8±11kg. Found the rhythm.
comment on [Concluded] 104 weeks. final numbers. thanks for reading. in c/dosinglogs · 6 points · 19 days ago
the boring consistency is the point
comment on my gallbladder came out at month 7 and i would still do it again in c/sideeffects · 26 points · 22 days ago
The practical rule people converge on is 28 days at fridge temperature after first puncture, and that comes from the preservative, not the peptide.