When it comes to e-liquid manufacturing, I think there should be some standardization in the process, as well as in where the chemicals are coming from that are being placed into the liquid solution, so there are a few answers to that question.
As for the amount of nicotine that should be in the product, that would depend on the absorption rate of the nicotine itself. If you look at any NHP nicotine products, you're looking at less than 4 milligrams absorption. You're looking for something like that within the electronic cigarettes.
Typically, from the studies that have been done in the United States with the different levels of 15 milligrams, 10 milligrams, 8 milligrams, and 6 milligrams, you're still not achieving that level within electronic cigarettes. The major reason for this is that the majority of the absorption that takes place is actually taking place orally through the mouth, rather than through the lungs, which is what most studies are starting to show. So there are a couple of answers to that.
Again, nicotine absorption would depend as well on the element and the amount of heat produced, and also the acid-based composition of the product, so each solution can be a little bit different.