thats the solvent peak
#hplc-massspec 2025-02-24
Monday41 messages9 participantstimes are UTC
Highlights from this day
- VialBot — Verification log updated: ERP — evidence added, status unchanged. 12:46
- invoice_mismatch — a shoulder on a peak is information, and usually bad information, from memory 13:02
- invoice_mismatch — 214nm sees the amide backbone so it sees everything. 280 only sees aromatics 13:34
- forty_units — is a tailing factor of anything specific a problem 14:02
- forty_units — i have a number at about a third of what i expected, is that a charge state 14:30
whats a plus one dalton shift usually
shallow gradient
is monoisotopic or average mass the one on most certificates
integration difference
Verification log updated: ERP — evidence added, status unchanged.
🧪3🧊1
a shoulder on a peak is information, and usually bad information, from memory
🧪3
semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
monoisotopic and average diverge more the bigger the molecule. say which one you are quoting
thats co-elution
214nm sees the amide backbone so it sees everything. 280 only sees aromatics
😂17👍15⚠️10
two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
thats a charge state
run a blank
🎉3👍3
within inter-lab range
🎉10📈2👀2
has anyone ever had a result where the mass was right and the purity was wrong
💀2
is a tailing factor of anything specific a problem
📉18💀2🎉4
ms/ms or it isnt identity
[edited]i have a number at about a third of what i expected, is that a charge state
🙏2⚠️1🎉4
how do you spot a deletion in a sequence from mass alone
how do you tell co-elution from a clean single peak
baseline is drifting badly, is that the column or the mobile phase
plus 16 is oxidation
update on the earlier thing ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
whats a normal gradient for a peptide this size
❤️1✅2
tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5, ill dig out the number
how would a truncation sequence show up
plus 0.98 is deamidation
show me the spectrum
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column, take that with a pinch of salt
quick one shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
i was wrong about tailing factor. it is usually the injection or the pH, not the column
retention time is a hint
oxidation is about plus 15.99 Da and is usually methionine or tryptophan
coming back after 24 months, what changed in how you read these
if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
⚠️1
the first peak is the solvent. it is always the solvent
do the arithmetic
[edited]slightly off topic but a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
my peak has a shoulder on it, what does that usually mean