#hplc-massspec 2026-05-15

monoisotopic and average diverge more the bigger the molecule. say which one you are quoting

ask for the trace

i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer

baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column

ms/ms sequencing is the only thing i would call identity. everything else is circumstantial

is a tailing factor of anything specific a problem

thats the solvent peak

is monoisotopic or average mass the one on most certificates

retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily

if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic

integration difference

how much sample does a lab actually need for identity as well as purity

relative retention time against a standard is comparable between labs. absolute minutes are not

the honest position is that hobby-level interpretation of a chromatogram is worth something but not much, for what its worth

Inter-lab diff for lot C-4402: 96.8% vs 99.4%. Within expected range.

semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2

co-elution is the failure mode that a beautiful single peak is most likely to be hiding

i was wrong about tailing factor. it is usually the injection or the pH, not the column

two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly

Archive lookup: quiet.hours first appears in this channel on 2025-12-11.

nobody runs enough blanks, including me, n of 1 obviously

slightly off topic but if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
nobody runs enough blanks, including me