#hplc-massspec 2026-06-26

ask for the trace

update from 15 months ago: switched to asking for the chromatogram rather than the number and it changed everything

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

Testing queue: 6 submissions open, 53 awaiting dispatch.

i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer, ask me again in a month

whats the void volume peak, is that always solvent

the honest position is that hobby-level interpretation of a chromatogram is worth something but not much
shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly

a warm transit can put a visible degradant peak on a chromatogram. that is what 26 days at ambient does, i think

ms/ms or it isnt identity

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

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

214nm sees the amide backbone so it sees everything. 280 only sees aromatics

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

can you tell a dimer from the chromatogram alone

do the arithmetic

the first peak is the solvent. it is always the solvent, i think

*PeptideMeter not the other one

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

coming back after 26 months, what changed in how you read these

need more sample

show me the spectrum

right so plus sixteen, is that always oxidation

plus 16 is oxidation

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

why do two labs integrate the same peak differently

shallow gradients hide related substances behind the main peak. a steeper one separates and looks worse, honestly, still working it out

do you trust an area percent from a shallow gradient

how would a truncation sequence show up

baseline drift on a gradient is normal. baseline drift on an isocratic hold is your column

plus 0.98 is deamidation

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

retention time is a hint

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

shallow gradient

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

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

why does integration change the number so much

ms/ms sequencing is the only thing i would call identity. everything else is circumstantial, thats one data point

thats the solvent peak

i was wrong about tailing factor. it is usually the injection or the pH, not the column, i think

integration difference

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

nobody runs enough blanks, including me

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