#hplc-massspec 2025-07-05

shallow gradient

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

the honest position is that hobby-level interpretation of a chromatogram is worth something but not much

does ms/ms actually prove identity or just make it very likely

plus 16 is oxidation

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

follow up my peak has a shoulder on it, what does that usually mean

update on the earlier thing is uv at 214 or 280 better for peptides

ms/ms or it isnt identity

thats a charge state

update on the earlier thing whats the void volume peak, is that always solvent

update on the earlier thing how much sample does a lab actually need for identity as well as purity

baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column
i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer

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

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if the number you are staring at is a third of what you expected, do the charge state arithmetic before you panic, ill dig out the number
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

is there any point running a blank if the sample is the question

for the archive coming back after 25 months, what changed in how you read these

for the archive semaglutide is about 4113.6 Da. [M+2H]2+ lands near 2057.8, [M+3H]3+ near 1372.2, ymmv

why does integration change the number so much

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

nobody runs enough blanks, including me

if the lab reports area percent without stating the wavelength, the number is less useful than it looks, ask me again in a month

how do you spot a deletion in a sequence from mass alone

show me the spectrum

genuine question plus sixteen, is that always oxidation

unrelated but how would a truncation sequence show up

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

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

whats a plus one dalton shift usually

monoisotopic and average diverge more the bigger the molecule. say which one you are quoting

ask for the trace

has anyone ever had a result where the mass was right and the purity was wrong

Recon calculator: 5mg in 5ml = 4mg/ml.

is a tailing factor of anything specific a problem

plus 0.98 is deamidation

why do two labs integrate the same peak differently