I also have Purillum Sweet Tobacco (that I love) and it has a "nutty" flavor but doesn't bother me at all (I assume that is AP) so I am suspecting acetoin myself.
Well...the
flavoring that's often abbreviated "AP", that gives eliquid a "nutty" flavor...is Acetyl
Pyrazine.
When you read that there are trace amounts of A & AP, or just 1 or the other, in buttery tasting flavorings, some creams, custards, and others....the "A" is Acetoin and
that "AP" is Acetyl
Propionyl.
About your butterscotch tasting eliquid - I know that TFA Butterscotch flavoring
has both A & AP in it. However, I haven't checked on other brands of it, to know for sure about them.