if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
#hplc-massspec 2026-03-13
Friday21 messages4 participantstimes are UTC
Highlights from this day
- stack_sceptic — if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic 19:23
- stack_sceptic — semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2 19:24
- gradient_greg — sorry to jump in shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly 19:26
- blank_run — for the archive coming back after 25 months, what changed in how you read these 21:01
- gradient_greg — two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly 22:19
semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
❤️6
for the archive how much sample does a lab actually need for identity as well as purity
sorry to jump in shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
plus 0.98 is deamidation
i was wrong about tailing factor. it is usually the injection or the pH, not the column
how do you spot a deletion in a sequence from mass alone
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
truncations show as a mass deficit matching one or more residues. you need the sequence to say which
thats a charge state
integration difference
for the archive coming back after 25 months, what changed in how you read these
🧊10
is a tailing factor of anything specific a problem
a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
sorry to jump in is uv at 214 or 280 better for peptides
retention time is a hint
if the lab reports area percent without stating the wavelength, the number is less useful than it looks
genuine question can you tell a dimer from the chromatogram alone
two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial