Topic
Mass spectrometry
Page 8 of 15 — Monoisotopic versus average mass, multiply-charged ions and the arithmetic, and why MS/MS is the only real identity test.
Messages — page 8 of 15
HPLC_Hankmonoisotopic and average diverge more the bigger the molecule. say which one you are quoting, ymmv#hplc-massspec · 2025-12-17HPLC_Hankupdate on the earlier thing ms/ms sequencing is the only thing i would call identity. everything else is circumstantial#hplc-massspec · 2025-12-17assay_not_purityms/ms or it isnt identity#hplc-massspec · 2025-12-18assay_not_puritytirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5#hplc-massspec · 2025-12-18logrotatesemaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2, still working it out#hplc-massspec · 2025-12-19coa_or_copethats a charge state#hplc-massspec · 2025-12-19ferrous_ashfollow up is monoisotopic or average mass the one on most certificates#hplc-massspec · 2025-12-19coa_or_copems/ms sequencing is the only thing i would call identity. everything else is circumstantial#hplc-massspec · 2025-12-19karl_fischerthats a charge state#hplc-massspec · 2025-12-20glasgow_vialdoes ms/ms actually prove identity or just make it very likely#hplc-massspec · 2026-01-03vienna_vialms/ms sequencing is the only thing i would call identity. everything else is circumstantial, ask me again in a month#hplc-massspec · 2026-01-03LC_MS_Lenamonoisotopic and average diverge more the bigger the molecule. say which one you are quoting#hplc-massspec · 2026-01-03pinch_not_stretchif the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic, someone…#hplc-massspec · 2026-01-03tokyo_tapersemaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2#hplc-massspec · 2026-01-03plus_sixteenms/ms or it isnt identity#hplc-massspec · 2026-01-03rotate_the_sitefor the archive tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5 co-elution is the failure mode that a…#hplc-massspec · 2026-01-04chaser_chrisif the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic#hplc-massspec · 2026-01-06chaser_chrisif somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result#hplc-massspec · 2026-01-06void_volumethats a charge state#hplc-massspec · 2026-01-06area_percentis monoisotopic or average mass the one on most certificates#hplc-massspec · 2026-01-06void_volumetirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5, n of 1 obviously#hplc-massspec · 2026-01-06chaser_chrissemaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2#hplc-massspec · 2026-01-06step_one_siandeamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant#hplc-massspec · 2026-01-06step_one_sianms/ms or it isnt identity#hplc-massspec · 2026-01-06marrow.modoxidation is about plus 15.99 Da and is usually methionine or tryptophan#hplc-massspec · 2026-01-07back_from_awaydoes ms/ms actually prove identity or just make it very likely 214nm sees the amide backbone so it sees everything. 280 only…#hplc-massspec · 2026-01-09LC_MS_Lenathats a charge state#hplc-massspec · 2026-01-09back_from_awaydeamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant#hplc-massspec · 2026-01-09cold_chain_cmdrtirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5#hplc-massspec · 2026-01-11ferrous_ashmonoisotopic and average diverge more the bigger the molecule. say which one you are quoting, thats one data point#hplc-massspec · 2026-01-11sharps_bin_sidsorry to jump in i have a number at about a third of what i expected, is that a charge state#hplc-massspec · 2026-01-11vialkeeperms/ms sequencing is the only thing i would call identity. everything else is circumstantial#hplc-massspec · 2026-01-11deamidationis monoisotopic or average mass the one on most certificates#hplc-massspec · 2026-01-12see_a_clinicianthats a charge state#hplc-massspec · 2026-01-12LC_MS_Lenai have a number at about a third of what i expected, is that a charge state#hplc-massspec · 2026-01-12sharps_bin_sidupdate 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 · 2026-01-14never_for_saleif the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic, thats just me#hplc-massspec · 2026-01-15alt_ast_aliquick one monoisotopic and average diverge more the bigger the molecule. say which one you are quoting#hplc-massspec · 2026-01-15cross_border_camsemaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2#hplc-massspec · 2026-01-15salt_bridgeyou pay for mass spec. Janoshik will tell you what is actually in there, not just how pure the thing you hoped for was#retatrutide · 2026-01-16slow.taperdoes ms/ms actually prove identity or just make it very likely two labs a point or two apart on the same lot is normal and…#hplc-massspec · 2026-01-16first_month_fithats a charge state#hplc-massspec · 2026-01-18peak_splitif somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result#hplc-massspec · 2026-01-18no_escrow_natedeamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant#hplc-massspec · 2026-01-18hk_hplcdoes ms/ms actually prove identity or just make it very likely#hplc-massspec · 2026-01-23endotoxin_edmonoisotopic and average diverge more the bigger the molecule. say which one you are quoting#hplc-massspec · 2026-01-23hk_hplcis monoisotopic or average mass the one on most certificates#hplc-massspec · 2026-01-23warsaw_vialms/ms or it isnt identity#hplc-massspec · 2026-01-23never_for_saletirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5#hplc-massspec · 2026-01-23never_for_saledeamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant#hplc-massspec · 2026-01-23never_for_salems/ms sequencing is the only thing i would call identity. everything else is circumstantial#hplc-massspec · 2026-01-23assay_not_purityif somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result, n of 1 obviously#hplc-massspec · 2026-01-23assay_not_purityif the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic, ill dig out…#hplc-massspec · 2026-01-23two_four_ceilingthats a charge state#hplc-massspec · 2026-01-24tesa_tesstirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5, thats just me#hplc-massspec · 2026-01-24tesa_tessms/ms sequencing is the only thing i would call identity. everything else is circumstantial, n of 1 obviously#hplc-massspec · 2026-01-24still_here_2024oxidation is about plus 15.99 Da and is usually methionine or tryptophan#hplc-massspec · 2026-01-24vienna_vialdeamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant#hplc-massspec · 2026-01-25fridge_thermoif somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result#hplc-massspec · 2026-01-25tail_factordoes ms/ms actually prove identity or just make it very likely#hplc-massspec · 2026-01-25