#hplc-massspec 2025-11-13

oxidation is about plus 15.99 Da and is usually methionine or tryptophan

whats the void volume peak, is that always solvent

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

why does integration change the number so much

shallow gradient

a dimer usually shows up late and at roughly double the mass. the chromatogram alone will not tell you

relative retention time against a standard is comparable between labs. absolute minutes are not

unrelated but a certificate with a number and no chromatogram is asking you to trust the integration you cannot see

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

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

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

tirzepatide is about 4813.5 Da, so 2+ is near 2407.8 and 3+ near 1605.5

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

plus 0.98 is deamidation

show me the spectrum

need more sample

214nm sees the amide backbone so it sees everything. 280 only sees aromatics, we shall see