Up until now, the industry usually used ‘freebase nicotine’. Basically, nicotine itself is a base which is not very strong: the protons must be removed in order to prevent the nicotine molecules from becoming ions. Ions do not move through membranes very well and therefore do not affect the body much. De-protonating the nicotine or making it ‘freebase’ allows it to do so.
In order to create freebase nicotine companies use a negatively charged ammonia which strips away protons. After separating the nicotine from the salts it is able to be extracted with steam.
Nicotine salt was discovered when experts explored the differences in chemical composition between cigarettes and e-cigarettes: nicotine salts instead of free-base nicotine increased nicotine blood absorption. However, salt requires more heat in order to be inhaled and absorbed properly.
Nicotine salts are the natural state of nicotine in the tobacco leaf.