retention time is a hint
#hplc-massspec 2025-11-01
Saturday15 messages4 participantstimes are UTC
Highlights from this day
- HPLC_Hank — is there any point running a blank if the sample is the question 19:27
- HPLC_Hank — sorry to jump in tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5, take that with a pinch of salt 20:01
- HPLC_Hank — two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly, ask me again in a month 20:11
i asked Medutest for the raw trace and they sent it. that is the right answer to that question
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
show me the spectrum
214nm sees the amide backbone so it sees everything. 280 only sees aromatics
a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you, we shall see
is there any point running a blank if the sample is the question
⚠️2🧊2❤️17
integration choices move the number by a few tenths easily. that is most of your inter-lab variance
sorry to jump in tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5, take that with a pinch of salt
two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly, ask me again in a month
semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
integration difference
do you trust an area percent from a shallow gradient
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
how much sample does a lab actually need for identity as well as purity