The term "USP" has meaning in and of itself. There is a scale from seven (7) to one (1) for purity. One (1) being the most pure, seven (7) the least.
USP is number three (3): "A chemical grade of sufficient purity to meet or exceed requirements of the U.S. Pharmacopeia (USP); acceptable for food, drug, or medicinal use; may be used for most laboratory purposes."
Hence any nicotine that is of "USP" purity would be considered by established science to be a product usable in any context for which that chemical is appropriate. By this I mean that it is considered "pure nicotine" and not some FDA-defined mish-mash of tobacco alkaloids.
These are scientific standards that apply to all manner of chemicals covered by the US Formulary, not just nicotine. (Look up the USP formulary web sites.)
Now if one inspects a site such as nicSelect we see this claim "NicSelect doesn’t just meet – it exceeds U.S. Pharmacopeia standards." Below you'll see a list of chemicals, the maximum specific level of impurity required by the standard, and how nicSelect exceeds them (has fewer impurities).
I will argue that while the FDA could attempt to argue that, for example, nicSelect nicotine is "derived from tobacco" such an interpretation would imply that any USP-grade chemical that was sufficiently pure for a USP designation would not be what it was but in fact what it was derived from.
More absolute nonsense as I originally postulated.
So while one can argue nano- and micro-gram amounts of nicotine in second hand smoke or vapor, for example, these standards are simply not applicable here.
Effectively the FDA would have to single out nicotine as somehow "magical" in the sense that only it remained a tobacco product once it was sufficiently pure to receive a "USP" designation.
More importantly bypassing the intent of the legislature which specifically identifies the formularly.
I find it hard to imagine, and in fact in the legislation linked above it is not present, there would be any special meaning for nicotine outside the actual statutes.
So while the FDA and Mr. Zeller can say whatever they like they would have to undo a lot of established science to create the fiction that USP nicotine was somehow a tobacco product.
So, as they say, stick that in your pipe and smoke it...