do the arithmetic
coa-h-2814.pdf
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#hplc-massspec 2026-06-08
Monday35 messages8 participantstimes are UTC
Highlights from this day
- vienna_vial — how would a truncation sequence show up 03:26
- vienna_vial — plus sixteen, is that always oxidation 03:40
- early_satiety — baseline is drifting badly, is that the column or the mobile phase if the number you are staring at is a third of what you expected, do the charge state arithmetic… 04:57
- food_noise_off — i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer a certificate with a number and no chromatogram is asking you… 07:05
- food_noise_off — follow up has anyone ever had a result where the mass was right and the purity was wrong nobody runs enough blanks, including me 07:08
show me the spectrum
how would a truncation sequence show up
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plus sixteen, is that always oxidation
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thats the solvent peak
whats the void volume peak, is that always solvent
thats a charge state
ms/ms or it isnt identity
two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly
baseline is drifting badly, is that the column or the mobile phase
if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
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i have a number at about a third of what i expected, is that a charge state
within inter-lab range
does ms/ms actually prove identity or just make it very likely
sorry to jump in you need more sample for identity than for purity. plan for that when you post it, thats just me
is monoisotopic or average mass the one on most certificates
*Janoshik not the other one
is a tailing factor of anything specific a problem
plus 16 is oxidation
how do you spot a deletion in a sequence from mass alone
i was wrong about tailing factor. it is usually the injection or the pH, not the column
retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily
sorry to jump in a warm transit can put a visible degradant peak on a chromatogram. that is what 8 days at ambient does
214nm sees the amide backbone so it sees everything. 280 only sees aromatics
if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
why does integration change the number so much
while im here nobody runs enough blanks, including me
i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
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follow up has anyone ever had a result where the mass was right and the purity was wrong
nobody runs enough blanks, including me
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is there any point running a blank if the sample is the question
ms/ms sequencing is the only thing i would call identity. everything else is circumstantial
sorry to jump in how do you tell co-elution from a clean single peak
if the lab reports area percent without stating the wavelength, the number is less useful than it looks
need more sample
deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant