Why did the FDA approve a certain vape after 7 years off the market?

The only thing you have to do to turn nicotine into nicotinic acid is oxidize it. Organic compounds oxidize at certain temperatures. The tobacco in a cigarette is slowly subjected to higher temps as the cherry approaches, so at some point it produces nicotinic acid, vital for good health.

Vapes are constant temp, and the newly approved are almost certainly not the temp you want to derive beneficial components.

Here's something I found helpful in understanding, particularly the last paragraph and shaded area following.

https://www.e-cigarette-forum.com/blog-entry/effects-of-heat-on-nicotine-degradation.6202/

>>14791041

The layman's version is that the heat can turn nicotine alkaloids into different alkaloids, ones that would still test positive as nicotine in a titration test but might not have the same stimulant effect on the human body.

One issue you might wish to keep in mind is that nicotine oxidation, while it results in a net loss of nicotine, does not result in a net loss of alkaloid content. In other words, some of the nicotine might chemically oxidize to one or more nicotine-like compounds with molecular weights very close to nicotine. The nitrogen of interest in a BTB titration is the nitrogen on the pyrollidine ring. The nitrogen on the pyridine ring is much less basic and really doesn't start to protonate until pH levels much below the yellow BTB endpoint are reached. This means that while nicotine actually possesses two basic nitrogens, it behaves with BTB as if it were a mono-base. The tricky point to keep in mind is that while nicotine oxidation products may be formed, these products will likely retain the basic character of their parent compound (nicotine). As a result, you could end up with 90% nicotine and 10% nicotine oxidation products, but a titration would still see it all as nicotine at the beginning concentration due to the fact that the titration is very non-selective, seeing only the pyrollidine nitrogen as relevant to the titration result.

https://www.e-cigarette-forum.com/blog-entry/effects-of-heat-on-nicotine-degradation.6202/