tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5
#hplc-massspec 2025-06-08
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Highlights from this day
- swab_dry_first — follow up how do you tell co-elution from a clean single peak 17:45
- monoisotopic — sorry to jump in if the lab reports area percent without stating the wavelength, the number is less useful than it looks 17:47
- swab_dry_first — a shoulder on a peak is information, and usually bad information 17:54
does ms/ms actually prove identity or just make it very likely
nobody runs enough blanks, including me
is a tailing factor of anything specific a problem
deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
for the archive monoisotopic and average diverge more the bigger the molecule. say which one you are quoting
ask for the trace
follow up shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
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has anyone ever had a result where the mass was right and the purity was wrong
do the arithmetic
whats the void volume peak, is that always solvent
thats the solvent peak
a warm transit can put a visible degradant peak on a chromatogram. that is what 12 days at ambient does
is monoisotopic or average mass the one on most certificates
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within inter-lab range
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the first peak is the solvent. it is always the solvent
thats a charge state
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follow up how do you tell co-elution from a clean single peak
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sorry to jump in if the lab reports area percent without stating the wavelength, the number is less useful than it looks
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 -> consistenta shoulder on a peak is information, and usually bad information
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how would a truncation sequence show up
a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
while im here baseline is drifting badly, is that the column or the mobile phase
co-elution is the failure mode that a beautiful single peak is most likely to be hiding
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
update from 22 months ago: switched to asking for the chromatogram rather than the number and it changed everything
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why does integration change the number so much
for the archive oxidation is about plus 15.99 Da and is usually methionine or tryptophan, happy to be corrected
need more sample
show me the spectrum
i was wrong about tailing factor. it is usually the injection or the pH, not the column
for the archive how do you spot a deletion in a sequence from mass alone
integration choices move the number by a few tenths easily. that is most of your inter-lab variance
whats a plus one dalton shift usually
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
Batch lookup B-0329: 3 independent reports on file, earliest 2025-01-28.
why do two labs integrate the same peak differently
i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
slightly off topic but do you trust an area percent from a shallow gradient
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ok so can you tell a dimer from the chromatogram alone
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
i have a number at about a third of what i expected, is that a charge state