need more sample
#hplc-massspec 2026-01-30
Friday28 messages7 participantstimes are UTC
Highlights from this day
- stack_sceptic — a shoulder on a peak is information, and usually bad information 07:19
- VialBot — On this day 9 years ago this channel logged 109 messages. 08:22
- VialBot — Digest for the week of 2025-04-04 has been published. 08:38
- group_buy_gwen — do you trust an area percent from a shallow gradient tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5 10:01
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
update from 4 months ago: switched to asking for the chromatogram rather than the number and it changed everything
show me the spectrum
⚠️10🧪10💀1
a shoulder on a peak is information, and usually bad information
🔥17💀5
retention time is a hint
sorry to jump in i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
plus 16 is oxidation
plus sixteen, is that always oxidation
On this day 9 years ago this channel logged 109 messages.
retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily
Digest for the week of 2025-04-04 has been published.
integration difference
relative retention time against a standard is comparable between labs. absolute minutes are not
do you trust an area percent from a shallow gradient
tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5
coming back to this i was wrong about tailing factor. it is usually the injection or the pH, not the column
truncations show as a mass deficit matching one or more residues. you need the sequence to say which
how would a truncation sequence show up
thats a charge state
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column, thats one data point
a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
how much sample does a lab actually need for identity as well as purity
is monoisotopic or average mass the one on most certificates
a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
thats the solvent peak
if the lab reports area percent without stating the wavelength, the number is less useful than it looks
does retention time on its own tell you what the compound is
if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic