#hplc-massspec 2026-02-10

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

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

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

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

shallow gradient

i was wrong about tailing factor. it is usually the injection or the pH, not the column
if the lab reports area percent without stating the wavelength, the number is less useful than it looks

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

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

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

a warm transit can put a visible degradant peak on a chromatogram. that is what 9 days at ambient does, i could be wrong

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

i have had a lot where the mass was exactly right and the purity was 96.8. wrong question, right answer

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

show me the spectrum

run a blank

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a shoulder on a peak is information, and usually bad information

within inter-lab range

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

ask for the trace

thats a charge state

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

thats the solvent peak

do the arithmetic

ms/ms or it isnt identity

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

plus 0.98 is deamidation

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