plus 0.98 is deamidation
#hplc-massspec 2026-05-24
Sunday35 messages10 participantstimes are UTC
Highlights from this day
- void_volume — you need more sample for identity than for purity. plan for that when you post it, ask me again in a month 13:20
- yara_yields — relative retention time against a standard is comparable between labs. absolute minutes are not a certificate with a number and no chromatogram is asking you to trust… 14:17
- yara_yields — two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly 14:45
- cross_border_cam — i was wrong about tailing factor. it is usually the injection or the pH, not the column if the lab reports area percent without stating the wavelength, the number is… 14:48
- VialBot — Recon calculator: 30mg in 2.5ml = 10mg/ml. 16:14
tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5, still working it out
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
thats the solvent peak
the first peak is the solvent. it is always the solvent
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you need more sample for identity than for purity. plan for that when you post it, ask me again in a month
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a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
run a blank
whats a plus one dalton shift usually
thats a charge state
shallow gradient
relative retention time against a standard is comparable between labs. absolute minutes are not
a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
thats co-elution
two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
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do the arithmetic
a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
i was wrong about tailing factor. it is usually the injection or the pH, not the column
if the lab reports area percent without stating the wavelength, the number is less useful than it looks
slightly off topic but 214nm sees the amide backbone so it sees everything. 280 only sees aromatics
has anyone ever had a result where the mass was right and the purity was wrong
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column, happy to be corrected
if the lab reports area percent without stating the wavelength, the number is less useful than it looks, ask me again in a month
cross_border_cambaseline drift on a gradient is normal. baseline drift on an isocratic hold is your…
oxidation is about plus 15.99 Da and is usually methionine or tryptophan, i think
follow up whats the void volume peak, is that always solvent
i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
Recon calculator: 30mg in 2.5ml = 10mg/ml.
how much sample does a lab actually need for identity as well as purity
plus sixteen, is that always oxidation
i asked Medutest for the raw trace and they sent it. that is the right answer to that question
is a tailing factor of anything specific a problem
for the archive nobody runs enough blanks, including me
integration difference
right so my peak has a shoulder on it, what does that usually mean
[edited]retention time is a hint
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