if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result, from memory
#hplc-massspec 2025-11-08
Saturday31 messages8 participantstimes are UTC
Highlights from this day
- no_appetite_nia — if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result, from memory 16:35
- VialBot — Recon calculator: 20mg in 1ml = 2mg/ml. 16:38
- zoya_zeros — why does integration change the number so much 17:38
- no_appetite_nia — two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly 19:49
Recon calculator: 20mg in 1ml = 2mg/ml.
does retention time on its own tell you what the compound is
whats a normal gradient for a peptide this size
need more sample
right so baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
the first peak is the solvent. it is always the solvent
214nm sees the amide backbone so it sees everything. 280 only sees aromatics
within inter-lab range
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retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily
i have a number at about a third of what i expected, is that a charge state
genuine question can you tell a dimer from the chromatogram alone
[edited]is uv at 214 or 280 better for peptides
slightly off topic but how would a truncation sequence show up
run a blank
[edited]my peak has a shoulder on it, what does that usually mean
why does integration change the number so much
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i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
plus 0.98 is deamidation
if the lab reports area percent without stating the wavelength, the number is less useful than it looks
*Medutest not the other one
show me the spectrum
oxidation is about plus 15.99 Da and is usually methionine or tryptophan
why do two labs integrate the same peak differently
i asked Medutest for the raw trace and they sent it. that is the right answer to that question
two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
do you trust an area percent from a shallow gradient
you need more sample for identity than for purity. plan for that when you post it
how much sample does a lab actually need for identity as well as purity
coming back after 16 months, what changed in how you read these