if the lab reports area percent without stating the wavelength, the number is less useful than it looks, for what its worth
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#hplc-massspec 2026-03-12
Thursday38 messages7 participantstimes are UTC
Highlights from this day
- lyophile_liv — if the lab reports area percent without stating the wavelength, the number is less useful than it looks, for what its worth 21:40
- zoya_zeros — my peak has a shoulder on it, what does that usually mean 22:10
- triple_ag_tom — is a tailing factor of anything specific a problem 22:24
- lyophile_liv — right so a warm transit can put a visible degradant peak on a chromatogram. that is what 6 days at ambient does 22:35
- lyophile_liv — the honest position is that hobby-level interpretation of a chromatogram is worth something but not much 22:42
baseline is drifting badly, is that the column or the mobile phase
sorry to jump in i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer
shallow gradient
ask for the trace
need more sample
is there any point running a blank if the sample is the question
ok so 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
Recon calculator: 5mg in 3ml = 4mg/ml.
baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
my peak has a shoulder on it, what does that usually mean
how do you spot a deletion in a sequence from mass alone
show me the spectrum
a certificate with a number and no chromatogram is asking you to trust the integration you cannot see
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a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you
does retention time on its own tell you what the compound is
do the arithmetic
is a tailing factor of anything specific a problem
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how would a truncation sequence show up
retention time is a hint
thats the solvent peak
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 -> consistentright so a warm transit can put a visible degradant peak on a chromatogram. that is what 6 days at ambient does
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plus 16 is oxidation
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you need more sample for identity than for purity. plan for that when you post it
relative retention time against a standard is comparable between labs. absolute minutes are not
the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
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monoisotopic and average diverge more the bigger the molecule. say which one you are quoting, ill dig out the number
whats a plus one dalton shift usually
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coming back after 20 months, what changed in how you read these
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if somebody says they ran a mass spec and does not show you a spectrum, that is a claim, not a result
if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic
a shoulder on a peak is information, and usually bad information
[edited]shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly, for what its worth
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can you tell a dimer from the chromatogram alone
why do two labs integrate the same peak differently
coming back to this tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5
integration difference