Analytics
#hplc-massspec
Reversed phase, area %, charge states, +1 and +16. Bring a spectrum.
6.3Kmessages
228day logs
297participants
18threads
The instrument channel. C18 gradients, retention time as weak identity evidence, integration and baseline drift, co-elution hiding a related impurity, monoisotopic versus average mass, multiply-charged ions and the arithmetic, deamidation at plus one dalton, oxidation at plus sixteen, truncation sequences, and why MS/MS is the only real identity test.
Pinned in this channel
Retention time alone is not identity. Two different peptides can co-elute. If somebody says "we ran a mass spec" without showing you a spectrum, they have made a claim, not produced a result.
Charge states: a 4113 Da peptide shows up at about 2057 for [M+2H]2+ and about 1372 for [M+3H]3+. If the number you are looking at is a third of what you expected, do the arithmetic before you panic.
Activity, last 12 months
quietbusymax 63 in a day
Day logs by year
Most recent logs
2026-06-30ok so a certificate with a number and no chromatogram is asking you to trust the integration you cannot see13 msgs · 4 people2026-06-28baseline is drifting badly, is that the column or the mobile phase47 msgs · 10 people2026-06-27truncations show as a mass deficit matching one or more residues. you need the sequence to say which38 msgs · 7 people2026-06-26ask for the trace61 msgs · 14 people2026-06-23is monoisotopic or average mass the one on most certificates16 msgs · 4 people2026-06-20need more sample21 msgs · 5 people2026-06-19is there any point running a blank if the sample is the question20 msgs · 4 people2026-06-18retention time is a hint37 msgs · 9 people2026-06-17has anyone ever had a result where the mass was right and the purity was wrong monoisotopic and average diverge more…44 msgs · 10 people2026-06-16whats a plus one dalton shift usually26 msgs · 7 people2026-06-14sorry to jump in integration choices move the number by a few tenths easily. that is most of your inter-lab variance42 msgs · 9 people2026-06-13does retention time on its own tell you what the compound is co-elution is the failure mode that a beautiful single…14 msgs · 4 people2026-06-12retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily24 msgs · 5 people2026-06-08do the arithmetic35 msgs · 8 people2026-06-06thats the solvent peak14 msgs · 5 people2026-06-04you need more sample for identity than for purity. plan for that when you post it18 msgs · 4 people2026-06-03within inter-lab range13 msgs · 4 people2026-05-31right so integration choices move the number by a few tenths easily. that is most of your inter-lab variance58 msgs · 11 people2026-05-30coming back to this does retention time on its own tell you what the compound is a certificate with a number and no…43 msgs · 10 people2026-05-29semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.229 msgs · 6 people2026-05-25thats the solvent peak22 msgs · 6 people2026-05-24plus 0.98 is deamidation35 msgs · 10 people2026-05-23coming back to this how much sample does a lab actually need for identity as well as purity23 msgs · 6 people2026-05-20shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly52 msgs · 12 people2026-05-19deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant22 msgs · 5 people2026-05-18Channel stats, last 30 days: 58 messages from 9 members.50 msgs · 11 people2026-05-17oxidation is about plus 15.99 Da and is usually methionine or tryptophan18 msgs · 5 people2026-05-16baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column, from memory16 msgs · 4 people2026-05-15monoisotopic and average diverge more the bigger the molecule. say which one you are quoting28 msgs · 9 people2026-05-14you need more sample for identity than for purity. plan for that when you post it, not advice obviously41 msgs · 9 people
Threads spun off from this channel
is there any point running a blank if the2026-05-30 · 11 msgsa warm transit can put a visible degradant peak2026-05-13 · 9 msgstwo labs a point or two apart on the2026-04-24 · 11 msgsupdate on the earlier thing whats a plus one2026-04-12 · 9 msgsyou need more sample for identity than for purity2026-03-30 · 6 msgsretention time is a hint, not a fingerprint. two2026-03-28 · 13 msgsdoes retention time on its own tell you what2026-03-14 · 13 msgsmy peak has a shoulder on it, what does2026-03-12 · 17 msgsok so a warm transit can put a visible2026-03-11 · 8 msgsbaseline is drifting badly, is that the column or2025-12-03 · 7 msgsa certificate with a number and no chromatogram is2025-11-16 · 10 msgsa warm transit can put a visible degradant peak2025-07-28 · 11 msgsdo you trust an area percent from a shallow2025-05-10 · 15 msgswould a group quantity-only round be worth funding2025-04-20 · 6 msgsif the lab reports area percent without stating the2025-04-08 · 17 msgsunrelated but retention time is a hint, not a2025-03-19 · 10 msgshow much sample does a lab actually need for2025-03-10 · 7 msgsif somebody says they ran a mass spec and2024-11-17 · 5 msgs