i asked VendorInvestigate for the raw trace and they sent it. that is the right answer to that question
#hplc-massspec 2025-05-25
Sunday29 messages7 participantstimes are UTC
Highlights from this day
- auckland_aliquot — coming back to this has anyone ever had a result where the mass was right and the purity was wrong 11:25
- amsterdam_aliquot — two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly i asked Janoshik for the raw trace and they sent it.… 12:31
- septum_sal — baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column 13:12
- rezept_rolf — monoisotopic and average diverge more the bigger the molecule. say which one you are quoting integration choices move the number by a few tenths easily. that is most… 14:33
- identity_shift — nobody runs enough blanks, including me, for what its worth a warm transit can put a visible degradant peak on a chromatogram. that is what 19 days at ambient does 15:01
unrelated but the first peak is the solvent. it is always the solvent, thats one data point
shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
how do you spot a deletion in a sequence from mass alone
thats the solvent peak
coming back after 12 months, what changed in how you read these
integration choices move the number by a few tenths easily. that is most of your inter-lab variance
update on the earlier thing plus sixteen, is that always oxidation
update from 10 months ago: switched to asking for the chromatogram rather than the number and it changed everything, i have it written down somewhere
plus 0.98 is deamidation
how would a truncation sequence show up
coming back to this has anyone ever had a result where the mass was right and the purity was wrong
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is monoisotopic or average mass the one on most certificates
does retention time on its own tell you what the compound is
*Janoshik not the other one
tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5
two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
i asked Janoshik for the raw trace and they sent it. that is the right answer to that question
a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
plus 16 is oxidation
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
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you need more sample for identity than for purity. plan for that when you post it
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
is a tailing factor of anything specific a problem
relative retention time against a standard is comparable between labs. absolute minutes are not
run a blank
my peak has a shoulder on it, what does that usually mean
monoisotopic and average diverge more the bigger the molecule. say which one you are quoting
integration choices move the number by a few tenths easily. that is most of your inter-lab variance
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how much sample does a lab actually need for identity as well as purity
nobody runs enough blanks, including me, for what its worth
a warm transit can put a visible degradant peak on a chromatogram. that is what 19 days at ambient does