follow up if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
#hplc-massspec 2024-12-08
Sunday26 messages6 participantstimes are UTC
Highlights from this day
- swirl_not_shake — how would a truncation sequence show up 21:32
- HPLC_Hank — you need more sample for identity than for purity. plan for that when you post it i asked Janoshik for the raw trace and they sent it. that is the right answer to… 21:41
- ms_ms_mira — how much sample does a lab actually need for identity as well as purity 21:48
- fibre_first — i have a number at about a third of what i expected, is that a charge state shallow gradients hide related substances behind the main peak. a steeper one separates… 21:58
- hydrate_hana — how do you tell co-elution from a clean single peak 22:54
truncations show as a mass deficit matching one or more residues. you need the sequence to say which
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial, your mileage will differ
do the arithmetic
how would a truncation sequence show up
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if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
ms/ms or it isnt identity
you need more sample for identity than for purity. plan for that when you post it
i asked Janoshik for the raw trace and they sent it. that is the right answer to that question
how much sample does a lab actually need for identity as well as purity
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tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5
i have a number at about a third of what i expected, is that a charge state
shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
thats the solvent peak
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a shoulder on a peak is information, and usually bad information
ask for the trace
M = 4113.6
[M+2H]2+ = (4113.6 + 2.02) / 2 = 2057.8
[M+3H]3+ = (4113.6 + 3.02) / 3 = 1372.2
observed 1372.3 -> consistenti was wrong about tailing factor. it is usually the injection or the pH, not the column
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
is there any point running a blank if the sample is the question
is a tailing factor of anything specific a problem
nobody runs enough blanks, including me
plus sixteen, is that always oxidation
show me the spectrum
thats co-elution
coming back after 2 months, what changed in how you read these
how do you tell co-elution from a clean single peak
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214nm sees the amide backbone so it sees everything. 280 only sees aromatics
baseline is drifting badly, is that the column or the mobile phase