coming back to this how much sample does a lab actually need for identity as well as purity
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#hplc-massspec 2026-05-23
Saturday23 messages6 participantstimes are UTC
Highlights from this day
the first peak is the solvent. it is always the solvent
how do you tell co-elution from a clean single peak
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nobody runs enough blanks, including me
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ok so semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5
ask for the trace
baseline is drifting badly, is that the column or the mobile phase
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coming back after 22 months, what changed in how you read these
shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
is monoisotopic or average mass the one on most certificates
does ms/ms actually prove identity or just make it very likely
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integration difference
a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
right so two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
a warm transit can put a visible degradant peak on a chromatogram. that is what 12 days at ambient does
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
oxidation is about plus 15.99 Da and is usually methionine or tryptophan
214nm sees the amide backbone so it sees everything. 280 only sees aromatics
unrelated but a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
how would a truncation sequence show up
why does integration change the number so much
whats a plus one dalton shift usually
why do two labs integrate the same peak differently