i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
#hplc-massspec 2026-03-06
Friday23 messages5 participantstimes are UTC
Highlights from this day
- salt_bridge — if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result, happy to be corrected 17:26
- baseline_drift — 214nm sees the amide backbone so it sees everything. 280 only sees aromatics 18:53
- baseline_drift — ok so nobody runs enough blanks, including me 19:12
- plateau_pen — retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily, ill dig out the number 19:16
is there any point running a blank if the sample is the question
oxidation is about plus 15.99 Da and is usually methionine or tryptophan
need more sample
a shoulder on a peak is information, and usually bad information
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result, happy to be corrected
i was wrong about tailing factor. it is usually the injection or the pH, not the column
thats the solvent peak
plus 0.98 is deamidation
why do two labs integrate the same peak differently
coming back after 18 months, what changed in how you read these
coming back to this why does integration change the number so much
shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
how would a truncation sequence show up
214nm sees the amide backbone so it sees everything. 280 only sees aromatics
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run a blank
ok so nobody runs enough blanks, including me
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retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily, ill dig out the number
for the archive ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
integration difference
thats a charge state
truncations show as a mass deficit matching one or more residues. you need the sequence to say which