#hplc-massspec 2025-05-01

Thursday19 messages5 participantstimes are UTC

Highlights from this day

karl_fischer — if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result 12:33
LC_MS_Lena — can you tell a dimer from the chromatogram alone 13:24
yyz_vial — co-elution is the failure mode that a beautiful single peak is most likely to be hiding 14:53
yyz_vial — a warm transit can put a visible degradant peak on a chromatogram. that is what 21 days at ambient does 15:05
fake_tracking — ms/ms sequencing is the only thing i would call identity. everything else is circumstantial, ask me again in a month 15:06

need more sample

if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result

[edited]

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deamidation is about plus 0.98 Da. it is not a rounding error, it is a degradant

within inter-lab range

i have a number at about a third of what i expected, is that a charge state

can you tell a dimer from the chromatogram alone

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retention time is a hint

does retention time on its own tell you what the compound is

baseline is drifting badly, is that the column or the mobile phase

integration choices move the number by a few tenths easily. that is most of your inter-lab variance, thats just me

if the lab reports area percent without stating the wavelength, the number is less useful than it looks

genuine question i asked VendorInvestigate for the raw trace and they sent it. that is the right answer to that question

how would a truncation sequence show up

ok so whats a plus one dalton shift usually

how much sample does a lab actually need for identity as well as purity

co-elution is the failure mode that a beautiful single peak is most likely to be hiding

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you need more sample for identity than for purity. plan for that when you post it

a warm transit can put a visible degradant peak on a chromatogram. that is what 21 days at ambient does

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ms/ms sequencing is the only thing i would call identity. everything else is circumstantial, ask me again in a month

M      = 4113.6
[M+2H]2+ = (4113.6 + 2.02) / 2 = 2057.8
[M+3H]3+ = (4113.6 + 3.02) / 3 = 1372.2
observed 1372.3 -> consistent