Adducts: sodium, potassium, and the peak you did not expect — does this still hold? posts 91–120

Marking my uncertainty on Adducts explicitly. I am confident about the direction, much less confident about the size, and not confident at all that it generalises past the case in the first post.

The failure mode on Adducts is boring rather than dramatic. It is almost always the step everyone assumes was done correctly because it is too simple to get wrong.

I read post #104 twice before replying, because I had assumed the opposite.

Adducts — sodium and potassium especially — shift the observed mass in predictable increments. A report showing an unexplained plus twenty-two is usually showing you a sodium adduct.

That matches what I was told, which is not the same as knowing it.

Post #107 answers the question as asked. The question underneath it is different.

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.

A weak preference rather than a position.

Adducts is a question about a distribution, not about a value, and treating it as a value is what produces the confident wrong answers.

Sensible. I would want the same detail before I acted on it either.

The arithmetic in post #109 is right; the assumption feeding it is the part to check.

Posting my Adducts numbers with the method attached so they can be discounted properly. Uncontrolled, unblinded, and collected by someone who wanted a particular answer.

Common adducts: sodium adds ≈22, potassium adds ≈38 compared to hydrogen. A [M+Na]+ peak is common and its mass is predictable from the base mass.

Adducts is a good example of a question where the honest answer is boring and the interesting answers are unsupported. I would go with boring.

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 have been on both sides of the Adducts argument in this category within eighteen months, which should tell you how strong the evidence for either side is.

Whatever the answer on Adducts turns out to be, the method for getting there is the same: state the assumption, do the arithmetic in public, invite the correction.

Clear enough that I do not think I have a follow-up, which is unusual.

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.

On Adducts, I would rather understate and be corrected upward than overstate and be quoted. That is a house style here and it is a good one.