#hplc-massspec 2025-09-06

if the lab reports area percent without stating the wavelength, the number is less useful than it looks

plus 16 is oxidation

Digest for the week of 2025-04-13 has been published.

monoisotopic and average diverge more the bigger the molecule. say which one you are quoting
a warm transit can put a visible degradant peak on a chromatogram. that is what 7 days at ambient does

thats a charge state

run a blank

retention time is a hint

unrelated but do you trust an area percent from a shallow gradient

baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
if the lab reports area percent without stating the wavelength, the number is less useful than it looks

ask for the trace

whats a normal gradient for a peptide this size

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

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

does ms/ms actually prove identity or just make it very likely

i asked VendorInvestigate for the raw trace and they sent it. that is the right answer to that question

oxidation is about plus 15.99 Da and is usually methionine or tryptophan, for what its worth

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