Mass spectrometry for identity confirmation: electrospray ionisation, multiple charge states, monoisotopic versus average mass, deconvolution, and what a mass shift of one, eighteen or one hundred and twenty-eight daltons tells you about what went wrong.
The particulars: identity confirmation by mass spectrometry · aspartimide formation · a GLP-1 receptor agonist. The comparison I want does not seem to exist anywhere…
The specifics, since they change the answer: +4 · 4207.2 Da. I would like the arithmetic checked rather than the conclusion asserted. I have deliberately not used an…
What I have: a sterility test · dimerisation · tirzepatide. I have used one of these for a while and I am considering switching, which requires a reason. What I care…
What I have: +2 · 4207.2 Da. This should be a straightforward calculation and I keep getting two different answers. The numbers are arbitrary; the method is what I am…
Conditions: +5 · 4113.6 Da. I want the working, not the result — I need to be able to redo it with different numbers. I care about the precision as well as the value…
The particulars: peptide mapping · oxidation · cagrilintide. I am trying to choose between two options that are usually discussed as though only one exists. I am not…
A vendor sent me a report showing a clean deconvolved mass at 4113.6 for semaglutide with, in their words, "no impurity peaks detected". Their sales copy turns that…
The case in front of me: +5 · 4813.5 Da. I want the working, not the result — I need to be able to redo it with different numbers. I care about the precision as well…
The specifics, since they change the answer: +4 · 3751.0 Da. I would rather understand the derivation than memorise the outcome. Two people I asked gave two answers…
For reference: +4 · 4731.3 Da. I would rather understand the derivation than memorise the outcome. Two people I asked gave two answers that differ by a factor of ten,…
What I am working with: an endotoxin test · racemisation · survodutide. I suspect the honest answer is that it depends, in which case I would like to know on what.…
I have been quoted roughly four times the price of a purity-plus-identity panel for something described as "tryptic digest with LC-MS/MS peptide mapping and sequence…
The method section is present, which is unusual enough that I want to make use of it. I have read the primary source rather than the summary, which has left me with…
Conditions: +5 · 4207.2 Da. I want the working, not the result — I need to be able to redo it with different numbers. I care about the precision as well as the value…
I have continuous temperature data for the period in question, which is unusual and I would like to use it. I would like the mechanism, because I want to be able to…
What I am working with: +3 · 4113.6 Da. I have worked this out and I would like someone to find the error, because I suspect there is one. My working so far, for the…
Details up front: +2 · 4113.6 Da. I can do the algebra. I am not confident about the conversion factors. If there is a standard way to lay this out, I would rather…
What I am working with: a residual-solvent screen · hydrolysis · ecnoglutide. Both of these get recommended confidently by different people, which suggests neither is…
I am comparing a supplier certificate against an independent result on the same lot. I would like help reading this properly rather than being told what conclusion to…
This is my second independent submission on material from the same supplier. I would rather understand the derivation than memorise the outcome. Two people I asked…
Numbers first: +2 · 4813.5 Da. This should be a straightforward calculation and I keep getting two different answers. The numbers are arbitrary; the method is what I…
The deconvolved mass spectrum on a tirzepatide report shows the expected 4813.5 peak plus three satellites I do not understand: one at 4795.5, one at 4814.5 that…
I have two third-party reports in front of me. Both say "identity confirmed by ESI-MS" and both include a spectrum, but the spectra look nothing like the single clean…
Setup, so nobody has to ask: +3 · 4813.5 Da. The units are where I keep going wrong, so please be explicit about them. I have sanity-checked the order of magnitude…
HPLC purity, identity confirmation and quantified content on the vial you actually hold. Reports arrive with the chromatogram attached, not just a number.
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