Quantitation by MS: most quantitation is done by LC-UV detection at 214 nm, not by MS, because extinction coefficients are better known. MS can quantify if an internal standard is used but that requires preparation.
Asking directly, because I could not find a straight answer: Adducts: sodium, potassium, and the peak you did not expect — does this still hold?
Adducts keeps being re-asked here and I think that is because the answer is conditional and the conditions never travel with it.
Attempting to write the conditional version down properly. Corrections welcome and expected — I would like this to end up as a maintained page rather than a fifth thread.
Post #2 answers the question as asked. The question underneath it is different.
Adducts is one of those subjects where the general answer and the answer for a specific case diverge, and the thread will go in circles until someone says which one is being asked for.
Second this, and I would have said it less carefully.
Narrowing post #6, because the general version has more than one answer.
Before the thread moves on from Adducts — what is the sample size behind the claim? I am not being difficult; I have seen the same figure quoted from an n of four and from an n of four hundred.
Quantitation by MS: most quantitation is done by LC-UV detection at 214 nm, not by MS, because extinction coefficients are better known. MS can quantify if an internal standard is used but that requires preparation.
Fine by me. I had wanted a stronger conclusion and there is not one available.
Post #8 put the caveat in the right place and I want to underline it.
Two claims get bundled together under Adducts and they need separating. The descriptive one — this is what was observed — is usually well supported. The causal one — this is why — usually is not.
Almost every disagreement in threads like this one dissolves once you say which of the two you are making.
The claim about Adducts upthread is stronger than its source supports. I have read the source. The source says "associated with" and the post says "causes".
On post #11 — agreed on the reasoning, with one qualification.
Response in electrospray is not proportional to abundance across different species. Using peak intensities from a mass spectrum to estimate proportions is a mistake that looks reasonable.
That is the shape of it. The detail is where I would expect to be corrected.
Trifluoroacetate adducts are common in material purified with TFA and are one reason a mass spectrum from a peptide can look busier than expected.
Adducts: I would want to see the raw numbers rather than the summary before agreeing. Summaries lose exactly the information that would settle this.
An observation about Adducts that I cannot explain and am posting anyway, on the principle that unexplained observations are more useful public than private.
This follows post #15 rather than contradicting it.
Resolution: "high resolution" commonly means <5 ppm across the mass range. Unit-resolution instruments achieve ±1 Da at best and cannot distinguish two species differing by less than 1 Da in total mass.
Written quickly, so the reasoning may be tighter than the wording.
Everything in post #15 holds. The case it does not cover is the one I have.
Second-hand on Adducts, so weight it accordingly — someone whose method I trust told me this and I have not verified it myself.
Taking post #20 at face value and following it one step further.
The version of Adducts that circulates here is a simplification of a simplification. It is not wrong, but it has lost the conditions under which it holds, and those conditions are where the interesting cases live.
Two people in this thread mean different things by Adducts and are disagreeing about the definition while believing they are disagreeing about the facts. Worth pausing to define it.
This follows post #24 rather than contradicting it.
Quantitation by MS: most quantitation is done by LC-UV detection at 214 nm, not by MS, because extinction coefficients are better known. MS can quantify if an internal standard is used but that requires preparation.
None of the above is medical advice and I am not qualified to give any.
Agreed on Adducts, with one qualification that I think matters. The reasoning holds for the case as described. Change the starting assumption and it does not, and the starting assumption is the part nobody states.
Taking Adducts seriously for a moment rather than deflecting: the honest position is that the community has observations and no controlled comparison, and those two things support very different sentences.
Coming back to post #26, because the follow-up matters more than the original answer.
Resolution: "high resolution" commonly means <5 ppm across the mass range. Unit-resolution instruments achieve ±1 Da at best and cannot distinguish two species differing by less than 1 Da in total mass.
If the premise is wrong, everything after it is decoration.
Adducts is well covered in the tag pages, and the older discussions are better than the recent ones because they were argued out properly. Worth twenty minutes before adding to this one.