truncations show as a mass deficit matching one or more residues. you need the sequence to say which
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#hplc-massspec 2026-04-18
Saturday26 messages7 participantstimes are UTC
Highlights from this day
- gus_charts — truncations show as a mass deficit matching one or more residues. you need the sequence to say which 22:58
- fridge_thermo — 214nm sees the amide backbone so it sees everything. 280 only sees aromatics, n of 1 obviously 23:12
- nine_nine_one — do you trust an area percent from a shallow gradient 23:46
- fridge_thermo — whats a normal gradient for a peptide this size 23:58
thats the solvent peak
shallow gradient
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deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
plus 16 is oxidation
how much sample does a lab actually need for identity as well as purity
plus 0.98 is deamidation
214nm sees the amide backbone so it sees everything. 280 only sees aromatics, n of 1 obviously
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ms/ms or it isnt identity
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result, still working it out
while im here a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
within inter-lab range
genuine question shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
integration choices move the number by a few tenths easily. that is most of your inter-lab variance
thats a charge state
coming back to this nobody runs enough blanks, including me, ill dig out the number
why does integration change the number so much
oxidation is about plus 15.99 Da and is usually methionine or tryptophan, happy to be corrected
run a blank
do the arithmetic
plus sixteen, is that always oxidation
do you trust an area percent from a shallow gradient
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quick one whats a plus one dalton shift usually
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how do you spot a deletion in a sequence from mass alone
whats a normal gradient for a peptide this size
medutest-report-e-2205.pdf
3 pages · 191 KB · not retained in the public archive