Adducts: sodium, potassium, and the peak you did not expect

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.

It is one reading of the data and not the only reasonable one.

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.

Where the adducts discussion usually stalls is that nobody wants to say "I do not know" and everyone is willing to say "it varies". Those are the same sentence with different clothes on.

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.

I would be interested in a counterexample if anyone has one.

Adding the measurement that post #43 says would settle it.

The honest summary of what a mass result buys you: it narrows the field of what the material could be, considerably. It never closes it, and no certificate should be read as though it had.

I would rather be precise about what I do not know than vague about what I do.

Where I would push back on the adducts consensus is the confidence, not the direction. The direction looks right. The confidence is borrowed.

The question underneath adducts is usually "how would I tell?" rather than "what is true?", and that one has a method attached to it.

Write down what you would expect to see under each hypothesis before you collect anything. If they predict the same observation, collecting it will not help.

Picking up post #65: that is the part I would want checked first.

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.

Adducts came up in a thread eighteen months ago and was answered well. I cannot find it, which is itself the problem, so here is the reconstruction.