has anyone ever had a result where the mass was right and the purity was wrong
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#hplc-massspec 2026-04-30
Thursday38 messages8 participantstimes are UTC
Highlights from this day
- hair_month_four — has anyone ever had a result where the mass was right and the purity was wrong 17:58
- food_noise_off — whats the void volume peak, is that always solvent 19:20
- hair_month_four — how do you spot a deletion in a sequence from mass alone 19:26
- LC_MS_Lena — tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5 19:44
two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
quick one a warm transit can put a visible degradant peak on a chromatogram. that is what 21 days at ambient does
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Inter-lab diff for lot C-4402: 99% vs 97.4%. Within expected range.
why do two labs integrate the same peak differently
thats the solvent peak
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
do the arithmetic
integration difference
medutest-report-b-0329.pdf
3 pages · 141 KB · not retained in the public archive
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nobody runs enough blanks, including me
a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
do you trust an area percent from a shallow gradient
nobody runs enough blanks, including me
my peak has a shoulder on it, what does that usually mean
relative retention time against a standard is comparable between labs. absolute minutes are not
need more sample
sorry to jump in you need more sample for identity than for purity. plan for that when you post it, i could be wrong
whats the void volume peak, is that always solvent
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show me the spectrum
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plus sixteen, is that always oxidation
how do you spot a deletion in a sequence from mass alone
janoshik-c-4402.pdf
2 pages · 922 KB · not retained in the public archive
run a blank
tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5
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thats a charge state
ms/ms or it isnt identity
for the archive if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
thats co-elution
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column, i have it written down somewhere
baseline is drifting badly, is that the column or the mobile phase
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semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2
plus 16 is oxidation
if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
ask for the trace
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i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
follow up shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly
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plus 0.98 is deamidation
within inter-lab range
oxidation is about plus 15.99 Da and is usually methionine or tryptophan
oxidation is about plus 15.99 Da and is usually methionine or tryptophan