Topic
Mass spectrometry
Page 14 of 15 — Monoisotopic versus average mass, multiply-charged ions and the arithmetic, and why MS/MS is the only real identity test.
Messages — page 14 of 15
sol_sendsis monoisotopic or average mass the one on most certificates#hplc-massspec · 2026-05-17monoisotopicfollow up if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result#hplc-massspec · 2026-05-17lyophile_livi have a number at about a third of what i expected, is that a charge state#hplc-massspec · 2026-05-17dexa_or_biasorry to jump in if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result#hplc-massspec · 2026-05-18dana_titratesfollow up does ms/ms actually prove identity or just make it very likely#hplc-massspec · 2026-05-18karl_fischertirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5#hplc-massspec · 2026-05-18willow_waitsoxidation is about plus 15.99 Da and is usually methionine or tryptophan#hplc-massspec · 2026-05-18tail_factorms/ms or it isnt identity#hplc-massspec · 2026-05-18karl_fischercoming back to this deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant#hplc-massspec · 2026-05-18HPLC_Hankms/ms sequencing is the only thing i would call identity. everything else is circumstantial#hplc-massspec · 2026-05-18HPLC_Hankoxidation is about plus 15.99 Da and is usually methionine or tryptophan, i have it written down somewhere#hplc-massspec · 2026-05-19LC_MS_Lenai have a number at about a third of what i expected, is that a charge state#hplc-massspec · 2026-05-19sulphur_burpif the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic#hplc-massspec · 2026-05-19freeze_thawms/ms or it isnt identity#hplc-massspec · 2026-05-20freeze_thawgenuine question ms/ms sequencing is the only thing i would call identity. everything else is circumstantial, thats one data…#hplc-massspec · 2026-05-20knees_firstmonoisotopic and average diverge more the bigger the molecule. say which one you are quoting#hplc-massspec · 2026-05-20blank_runchange the selectivity and see if the peak splits. shallower gradient, or a different stationary phase, or swap TFA for formic…#hplc-massspec · 2026-05-20blank_runthat last one is the good test and it is why LC-MS beats LC alone for this#hplc-massspec · 2026-05-20thirty_min_waitok so semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2 tirzepatide is about 4813.5 Da, so 2+…#hplc-massspec · 2026-05-23bengaluru_bacdoes ms/ms actually prove identity or just make it very likely#hplc-massspec · 2026-05-23monoisotopicoxidation is about plus 15.99 Da and is usually methionine or tryptophan 214nm sees the amide backbone so it sees everything.…#hplc-massspec · 2026-05-23juno_joinstirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5, still working it out ms/ms sequencing is the only…#hplc-massspec · 2026-05-24yara_yieldsdeamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant#hplc-massspec · 2026-05-24no_appetite_niaif somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result#hplc-massspec · 2026-05-24void_volumeoxidation is about plus 15.99 Da and is usually methionine or tryptophan, i think#hplc-massspec · 2026-05-24chlorhexms/ms or it isnt identity#hplc-massspec · 2026-05-25tarpit_tamsemaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2#hplc-massspec · 2026-05-29apob_over_ldlthats a charge state#hplc-massspec · 2026-05-29apob_over_ldloxidation is about plus 15.99 Da and is usually methionine or tryptophan#hplc-massspec · 2026-05-29tarpit_tamif the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic#hplc-massspec · 2026-05-29two_four_ceilingmonoisotopic and average diverge more the bigger the molecule. say which one you are quoting#hplc-massspec · 2026-05-29nordic_price_nilsms/ms or it isnt identity#hplc-massspec · 2026-05-30tesa_tessms/ms sequencing is the only thing i would call identity. everything else is circumstantial#hplc-massspec · 2026-05-30tesa_tessmonoisotopic and average diverge more the bigger the molecule. say which one you are quoting#hplc-massspec · 2026-05-30identity_shiftoxidation is about plus 15.99 Da and is usually methionine or tryptophan#hplc-massspec · 2026-05-30lead_time_larstirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5#hplc-massspec · 2026-05-30sharps_bin_siddoes ms/ms actually prove identity or just make it very likely#hplc-massspec · 2026-05-30peak_splitsemaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2#hplc-massspec · 2026-05-31tail_factoroxidation is about plus 15.99 Da and is usually methionine or tryptophan#hplc-massspec · 2026-05-31chlorhexmonoisotopic and average diverge more the bigger the molecule. say which one you are quoting#hplc-massspec · 2026-05-31fridge_thermoif somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result#hplc-massspec · 2026-05-31void_volumeupdate on the earlier thing if the number you are staring at is a third of what you expected, do the charge state arithmetic…#hplc-massspec · 2026-05-31rotate_the_sitetirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5, we shall see semaglutide is about 4113.6 Da. [M+2H]2+…#hplc-massspec · 2026-05-31stack_sceptici have a number at about a third of what i expected, is that a charge state#hplc-massspec · 2026-05-31back_from_awayms/ms or it isnt identity#hplc-massspec · 2026-05-31gus_chartsthats a charge state#hplc-massspec · 2026-05-31monoisotopicdeamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant#hplc-massspec · 2026-06-03void_volumeright so tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5#hplc-massspec · 2026-06-03acetate_ashms/ms or it isnt identity#hplc-massspec · 2026-06-03sedge_sourcesi have a number at about a third of what i expected, is that a charge state#hplc-massspec · 2026-06-04no_appetite_niathats a charge state#hplc-massspec · 2026-06-04sedge_sourcesif somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result#hplc-massspec · 2026-06-04sedge_sourcesoxidation is about plus 15.99 Da and is usually methionine or tryptophan, ill dig out the number#hplc-massspec · 2026-06-04sedge_sourcesdeamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant#hplc-massspec · 2026-06-04hk_hplcif somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result#hplc-massspec · 2026-06-06abdo_two_inchthats a charge state#hplc-massspec · 2026-06-08abdo_two_inchms/ms or it isnt identity#hplc-massspec · 2026-06-08typosquat_taydoes ms/ms actually prove identity or just make it very likely#hplc-massspec · 2026-06-08early_satietyis monoisotopic or average mass the one on most certificates#hplc-massspec · 2026-06-08HPLC_Hankif the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic#hplc-massspec · 2026-06-08