i have a number at about a third of what i expected, is that a charge state
#hplc-massspec 2025-09-16
Tuesday31 messages8 participantstimes are UTC
Highlights from this day
- relabel_watch — nobody runs enough blanks, including me 15:06
- relabel_watch — truncations show as a mass deficit matching one or more residues. you need the sequence to say which 15:12
- power_through_no — deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant, thats one data point 15:56
shallow gradient
ok so co-elution is the failure mode that a beautiful single peak is most likely to be hiding
can you tell a dimer from the chromatogram alone
nobody runs enough blanks, including me
👍9
integration difference
run a blank
[edited]sorry to jump in if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
truncations show as a mass deficit matching one or more residues. you need the sequence to say which
🧊1💀5❤️1
*VendorInvestigate not the other one
thats the solvent peak
📈12👍10🎉1
plus 16 is oxidation
ask for the trace
😂13
deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant, thats one data point
❤️3
need more sample
integration choices move the number by a few tenths easily. that is most of your inter-lab variance
deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
thats a charge state
semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
update from 10 months ago: switched to asking for the chromatogram rather than the number and it changed everything
is monoisotopic or average mass the one on most certificates
a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
show me the spectrum
does ms/ms actually prove identity or just make it very likely
baseline is drifting badly, is that the column or the mobile phase
update on the earlier thing does retention time on its own tell you what the compound is
do you trust an area percent from a shallow gradient
ms/ms or it isnt identity
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
how do you spot a deletion in a sequence from mass alone
a shoulder on a peak is information, and usually bad information
how much sample does a lab actually need for identity as well as purity