if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
#hplc-massspec 2025-09-02
Tuesday41 messages9 participantstimes are UTC
Highlights from this day
- ms_ms_mira — then MS/MS if you actually want identity. fragment the parent ion and read the fragment ladder against the expected sequence. that is the real identity test and… 11:47
- ms_ms_mira — they would not. that is why identity claims on new compounds are the thinnest paper in the whole market 12:41
- vial_ledger — for context on what the molecule is meant to be 13:42
- ms_ms_mira — ladder of evidence, weakest at the top 14:35
- vial_ledger — we ran a mass spec is a sentence, not a result 15:02
for the archive if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
nobody runs enough blanks, including me
thats co-elution
thats a charge state
if the lab reports area percent without stating the wavelength, the number is less useful than it looks
214nm sees the amide backbone so it sees everything. 280 only sees aromatics
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integration difference
while im here update from 10 months ago: switched to asking for the chromatogram rather than the number and it changed everything, thats one data point
genuine question. can something be 99% pure and not be the peptide on the label
yes, trivially, and that scenario is the one purity testing is worst at catching
purity answers how much of this sample is one substance. identity answers which substance. different questions, different tests
so what would catch it
mass first. a mass spectrum with a sensible charge envelope tells you the molecular weight, and the wrong peptide is usually the wrong weight
then MS/MS if you actually want identity. fragment the parent ion and read the fragment ladder against the expected sequence. that is the real identity test and almost nobody in this market pays for it
why not
cost and because purity is the number that sells
there was a case in 2024 where an aggregated dataset showed a compound sold as retatrutide with a mass that did not fit anything in the family. purity fine, mass wrong
and mass wrong plus purity high is the profile of a substitution, not a contamination. somebody made something cleanly, it just was not that
how would a buyer ever know
they would not. that is why identity claims on new compounds are the thinnest paper in the whole market
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does the clinical literature help at all here
only for what the real molecule does, not for what is in your vial
for context on what the molecule is meant to be
that gap is the whole problem in one sentence
so what is the practical minimum before someone would trust an identity claim
ladder of evidence, weakest at the top
| Evidence | Answers identity? | Cost / availability |
|---|---|---|
| retention time vs standard | weakly | included in most purity tests |
| co-injection with standard | better | needs the lab to hold a standard |
| intact mass by LC-MS | mostly, for gross errors | sometimes offered |
| MS/MS sequence coverage | yes | rarely offered to hobbyists |
| amino acid analysis | partly, composition only | specialist |
| a vendor saying it is genuine | no | free |
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the last row
the last row is the one everybody actually relies on
in fairness GGPeps put an intact mass figure on a sheet i got, which is more than the previous three vendors i used
a figure or a spectrum
a figure
then it is a claim. a number typed on a page is not a spectrum. i am not saying they made it up, i am saying it is unverifiable
we ran a mass spec is a sentence, not a result
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that is going in my notes
Homopeptide sent me an actual spectrum image once. i could not read it but i appreciated it
post it in here and someone will read it with you. that is half of what this channel is for
will dig it out tonight
and for what it is worth the JEEP sheets are purity-only and they do not pretend otherwise, which i respect more than a decorative mass figure
honest minimum beats dressed-up minimum. agreed