#hplc-massspec 2025-05-04

is a tailing factor of anything specific a problem
i asked VendorInvestigate for the raw trace and they sent it. that is the right answer to that question

a warm transit can put a visible degradant peak on a chromatogram. that is what 13 days at ambient does

right so how do you tell co-elution from a clean single peak

right so retention time is a hint, not a fingerprint. two different peptides can co-elute perfectly happily, for what its worth

while im here relative retention time against a standard is comparable between labs. absolute minutes are not, happy to be corrected

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

nobody runs enough blanks, including me
a shoulder on a peak is information, and usually bad information

plus sixteen, is that always oxidation

do the arithmetic

*Medutest not the other one

thats co-elution

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

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

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

why do two labs integrate the same peak differently

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

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

two labs a point or two apart on the same lot is normal and gets mistaken for one of them being wrong constantly

Batch lookup G-0641: 5 independent reports on file, earliest 2024-08-02.

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

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