shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
#hplc-massspec 2025-10-17
Friday27 messages7 participantstimes are UTC
Highlights from this day
- area_percent — ok so nobody runs enough blanks, including me 14:04
- power_through_no — you need more sample for identity than for purity. plan for that when you post it 16:17
- slow.taper — a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you 16:49
- power_through_no — a warm transit can put a visible degradant peak on a chromatogram. that is what 7 days at ambient does 16:53
integration difference
thats the solvent peak
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i was wrong about tailing factor. it is usually the injection or the pH, not the column, i have it written down somewhere
ok so nobody runs enough blanks, including me
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tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5
thats a charge state
need more sample
show me the spectrum
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plus 0.98 is deamidation
is uv at 214 or 280 better for peptides
do the arithmetic
update from 1 months ago: switched to asking for the chromatogram rather than the number and it changed everything
while im here integration choices move the number by a few tenths easily. that is most of your inter-lab variance
you need more sample for identity than for purity. plan for that when you post it
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ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
right so if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic, ymmv
truncations show as a mass deficit matching one or more residues. you need the sequence to say which
is monoisotopic or average mass the one on most certificates
while im here semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
ask for the trace
how do you tell co-elution from a clean single peak
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
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plus 16 is oxidation
a warm transit can put a visible degradant peak on a chromatogram. that is what 7 days at ambient does
fridge-thermometer.png
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