Topic
Mass spectrometry
Page 10 of 15 — Monoisotopic versus average mass, multiply-charged ions and the arithmetic, and why MS/MS is the only real identity test.
Messages — page 10 of 15
karl_fischerdeamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant#hplc-massspec · 2026-02-25vial_ledgermonoisotopic and average diverge more the bigger the molecule. say which one you are quoting#hplc-massspec · 2026-02-25LC_MS_Lenams/ms or it isnt identity#hplc-massspec · 2026-02-26LC_MS_Lenathats a charge state#hplc-massspec · 2026-02-26lean_mass_lexthats a charge state#hplc-massspec · 2026-02-28lean_mass_lexif somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result#hplc-massspec · 2026-02-28peak_splitmonoisotopic and average diverge more the bigger the molecule. say which one you are quoting#hplc-massspec · 2026-02-28fasting_insulinis monoisotopic or average mass the one on most certificates#hplc-massspec · 2026-03-01LC_MS_Lenawhile im here oxidation is about plus 15.99 Da and is usually methionine or tryptophan#hplc-massspec · 2026-03-01fasting_insulinsemaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2#hplc-massspec · 2026-03-01freeze_thawif somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result, not advice obviously#hplc-massspec · 2026-03-02two_four_ceilingdoes ms/ms actually prove identity or just make it very likely#hplc-massspec · 2026-03-02karl_fischeri have a number at about a third of what i expected, is that a charge state#hplc-massspec · 2026-03-02coa_or_copetirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5#hplc-massspec · 2026-03-02coa_or_copeis monoisotopic or average mass the one on most certificates#hplc-massspec · 2026-03-02coa_or_copems/ms or it isnt identity#hplc-massspec · 2026-03-02gradient_gregthats a charge state#hplc-massspec · 2026-03-02gradient_gregms/ms sequencing is the only thing i would call identity. everything else is circumstantial#hplc-massspec · 2026-03-02peak_splitdeamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant#hplc-massspec · 2026-03-02LC_MS_Lenadoes ms/ms actually prove identity or just make it very likely#hplc-massspec · 2026-03-04LC_MS_Lenaoxidation is about plus 15.99 Da and is usually methionine or tryptophan#hplc-massspec · 2026-03-04patent_2026oxidation is about plus 15.99 Da and is usually methionine or tryptophan#hplc-massspec · 2026-03-06salt_bridgeif 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#hplc-massspec · 2026-03-06salt_bridgethats a charge state#hplc-massspec · 2026-03-06void_volumesemaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2#hplc-massspec · 2026-03-08ollie_orderswhile im here does ms/ms actually prove identity or just make it very likely#hplc-massspec · 2026-03-08HPLC_Hankms/ms sequencing is the only thing i would call identity. everything else is circumstantial#hplc-massspec · 2026-03-08aliquot_adathats a charge state#hplc-massspec · 2026-03-11rowan_readsmonoisotopic and average diverge more the bigger the molecule. say which one you are quoting#hplc-massspec · 2026-03-11rowan_readstirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5, i could be wrong#hplc-massspec · 2026-03-11area_percentsemaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2#hplc-massspec · 2026-03-11lyophile_livok so oxidation is about plus 15.99 Da and is usually methionine or tryptophan#hplc-massspec · 2026-03-12lyophile_livmonoisotopic and average diverge more the bigger the molecule. say which one you are quoting, ill dig out the number#hplc-massspec · 2026-03-12electrolyte_eliif the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic#hplc-massspec · 2026-03-12ghent_gradientcoming back to this tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5#hplc-massspec · 2026-03-12stack_scepticif the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic#hplc-massspec · 2026-03-13stack_scepticthats a charge state#hplc-massspec · 2026-03-13gradient_gregms/ms sequencing is the only thing i would call identity. everything else is circumstantial#hplc-massspec · 2026-03-13batch_banditif somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result#hplc-massspec · 2026-03-14gradient_gregms/ms sequencing is the only thing i would call identity. everything else is circumstantial, thats just me#hplc-massspec · 2026-03-14no_appetite_niaunrelated but deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant#hplc-massspec · 2026-03-14per_mg_petesemaglutide 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.…#hplc-massspec · 2026-03-14deamidationtirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5#hplc-massspec · 2026-03-18new_here_natgot a mass spec printout with my order and the biggest peak is at 1372 which is nowhere near 4113 so i assume its fake#hplc-massspec · 2026-03-18logrotatethe arithmetic, do it once and you will never panic again#hplc-massspec · 2026-03-18logrotateand the approximatelys are doing work there. quote those to one decimal at most in chat, the exact figures depend on whether…#hplc-massspec · 2026-03-18logrotatemonoisotopic uses only the lightest isotope of every atom. average uses the natural abundance mix. for something small the two…#hplc-massspec · 2026-03-18still_here_2024which produces the endless it is 2 Da off, is it degraded panic#hplc-massspec · 2026-03-18quiet.hoursworth pinning the charge state block, this question comes up monthly#hplc-massspec · 2026-03-18logrotatedepends entirely on how much of it there is, and a mass spectrum is a poor way to judge how much. intensity in ESI is not…#hplc-massspec · 2026-03-18new_here_natso mass spec for identity, HPLC for how much#hplc-massspec · 2026-03-18elm_escalatesthe SSA sheet i have does exactly this properly, deconvoluted mass plus the charge states listed. it is the best MS page i…#hplc-massspec · 2026-03-18deamidationtirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5#hplc-massspec · 2026-03-23ghent_gradientupdate on the earlier thing ms/ms sequencing is the only thing i would call identity. everything else is circumstantial, thats…#hplc-massspec · 2026-03-23two_four_ceilingis monoisotopic or average mass the one on most certificates#hplc-massspec · 2026-03-23tail_factori have a number at about a third of what i expected, is that a charge state#hplc-massspec · 2026-03-24tail_factorif the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic you need…#hplc-massspec · 2026-03-24salt_bridgeoxidation is about plus 15.99 Da and is usually methionine or tryptophan#hplc-massspec · 2026-03-24ghent_gradientif somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result integration choices move…#hplc-massspec · 2026-03-24u100_patis monoisotopic or average mass the one on most certificates#hplc-massspec · 2026-03-24