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…
The case in front of me: a sterility test · dimerisation · tirzepatide. I have used one of these for a while and I am considering switching, which requires a reason.…
The specifics, since they change the answer: identity confirmation by mass spectrometry · ecnoglutide. I am trying to choose between two options that are usually…
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…
Details up front: BCH · identity confirmation by mass spectrometry. I have worked this out and I would like someone to find the error, because I suspect there is one.…
Details up front: QSC · identity confirmation by mass spectrometry. I have worked this out and I would like someone to find the error, because I suspect there is one.…
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…
Concretely: peptide mapping · oxidation · cagrilintide. I am trying to choose between two options that are usually discussed as though only one exists. I am not…
For reference: ERP · identity confirmation by mass spectrometry. I have worked this out and I would like someone to find the error, because I suspect there is one. My…
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,…
The specifics, since they change the answer: identity confirmation by mass spectrometry · a twenty-person split. I would like to define my thresholds before I have a…
The case in front of me: an endotoxin test · racemisation · survodutide. I suspect the honest answer is that it depends, in which case I would like to know on what.…
The method section is present, which is unusual enough that I want to make use of it. I suspect the honest answer is that it depends, in which case I would like to…
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…
The case in front of me: a residual-solvent screen · hydrolysis · ecnoglutide. Both of these get recommended confidently by different people, which suggests neither…
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