#hplc-massspec 2026-04-23

Thursday22 messages4 participantstimes are UTC

Highlights from this day

batch_bandit — integration choices move the number by a few tenths easily. that is most of your inter-lab variance 20:57
maple_maths — retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily, ask me again in a month 21:17
same_chromato — update on the earlier thing 214nm sees the amide backbone so it sees everything. 280 only sees aromatics, take that with a pinch of salt 21:37

integration choices move the number by a few tenths easily. that is most of your inter-lab variance

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you need more sample for identity than for purity. plan for that when you post it, take that with a pinch of salt

tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5, happy to be corrected

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

retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily, ask me again in a month

shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly

a warm transit can put a visible degradant peak on a chromatogram. that is what 17 days at ambient does

thats a charge state

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

update on the earlier thing 214nm sees the amide backbone so it sees everything. 280 only sees aromatics, take that with a pinch of salt

⚠️15

retention time is a hint

my peak has a shoulder on it, what does that usually mean

do you trust an area percent from a shallow gradient

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

a certificate with a number and no chromatogram is asking you to trust the integration you cannot see

ms/ms sequencing is the only thing i would call identity. everything else is circumstantial, n of 1 obviously

*Janoshik not the other one

truncations show as a mass deficit matching one or more residues. you need the sequence to say which, not advice obviously

if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result

[edited]

ask for the trace

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can you tell a dimer from the chromatogram alone

shallow gradient