Nicotine Salts Vs. Freebase Nicotine

Early generation e-cigarettes and – later on – vaporizers were notoriously inefficient. That was largely due to technically unrefined heating coils and “wicks” (basically cotton wool soaked in a freebase nicotine solution). For that reason, vapes were often loaded with e-liquids containing nicotine concentrations of up to 48 mg/ml or even higher to get a “hit” out of it; unimaginable today. Things could well have continued that way, but then the EU’s Tobacco Products Directive (TPD) came along. It legislated that nicotine in e-liquids was to be limited to a maximum of 20 mg/ml, more or less forcing vape manufacturers to put their back into R&D to improve their devices’ efficiency. In addition, advances concerning better batteries and sophisticated digital interfaces that allowed users to tailor their personal vaping experience were made. But these advances did not address the perhaps single most important key weakness of vaping at the time: the fact that many smokers who wanted to transition from tobacco to less harmful vaping did find the nicotine “rush” from vaping not as satisfying as what they were accustomed to from cigarettes.

What is freebase nicotine? 

Freebase nicotine is the “natural” molecular form of nicotine, i.e. it has not “bonded” with another substance to form a chemical compound. As freebase nicotine has always been readily available, it consequently became the primary active ingredient in e-liquids. Still used in many e-liquid brands today, it also is found in numerous other products, such as nicotine patches and pouches, lozenges, or gums. Extracted from tobacco leaves and purified, the substance easily dissolves in propylene glycol or vegetal glycerin to make e-liquids. However, besides freebase nicotine, tobacco leaves also contain a variety of nicotine salts, whereas the plants’ pH level determines whether nicotine is primarily present in it as freebase nicotine or as a salt. 

“In some cases, nicotine exists in the form of salt [in the plant], while in other cases it is present as the basic molecule,” explained Tom Xie, senior director of the SMOORE Research Center in Shenzhen, China. “Generally speaking, the higher the pH value [i.e. alkaline] in the tobacco plant, the higher the amount of nicotine in its pure form; and the lower the pH [i.e. acidic], the lower the amount of nicotine in its salt form,” he said. 

New possibilities with nicotine salts 

Defined in chemical terms, a “salt” is a compound consisting of an ionic assembly of positively charged cations and negatively charged anions, resulting in no net electric charge. In that respect, a nicotine salt can either form naturally in the tobacco leaf itself or – more commonly nowadays – it is chemically synthesized by suppliers such as Alchem, for example. But from whichever source they may come, nicotine salts offer amazing new possibilities for driving vaping industry innovation. Why is that so? What makes e-liquids containing one or another nicotine salt so different from e-liquids produced with freebase nicotine? Well, it all comes back to the already mentioned key weakness of early e-liquids. 

“When a nicotine salt is used in an e-liquid instead of freebase nicotine, it will greatly improve the vaping experience and taste perception, including providing “the smoothest draw and inhale,” explained Anna Balconi, technical manager of global nicotine supplier Alchem Europe SA. However, it is not all as easy as it may sound. 

A nicotine salt conundrum solved 

Nicotine salts are not the most effective way of delivering nicotine, because they cannot penetrate cell membranes easily and also are not easily vaporized. But a few decades ago, researchers at Philips Morris discovered a solution to that conundrum. Natural nicotine salts that occur in tobacco plants (and, hence, are also present in rag for making cigarettes) can actually be converted into the freebase form of nicotine in situ by conditioning the tobacco with another salt compound, for instance diammonium phosphate, which releases ammonium ions once the cigarette is combusted. These ions then react with the actual nicotine salt to release freebase nicotine. And it is that freebase nicotine released in situ which can subsequently cross cell membranes, becoming bioavailable. 

But, wait a minute! Doesn’t that mean that freebase nicotine would be the prime substance of choice for e-liquids in the first place? In theory, yes. However, when compared to its salt form, freebase nicotine is less stable. It is more susceptible to oxidation and the formation of impurities. “It has a high pH value, even higher than 8.0 or 9.0,” explained Anna Balconi. “This makes an e-liquid containing freebase nicotine considerably harsher on the throat, especially when the nicotine dose per ml is increased, which is particularly important for transitioning heavy smokers.” 

SMOORE’s Tom Xie additionally noted that freebase nicotine, when used in vapes, is absorbed more readily by the throat’s mucous membranes than nicotine salt. “That is the reason why freebase nicotine may cause excessive throat irritation, and it also does not make the satisfaction effect on the brain ideal,” he explained. “E-liquids with nicotine salts cause less throat irritation, thus provide more comfortable inhalation and also better nicotine addiction relief than freebase nicotine e-liquid.”

The temperature challenge 

Then there was the challenge of finding nicotine salt forms that are easily “vaporizable,” releasing freebase nicotine at the lower temperature ranges typical for vaping devices. The answer once again was found in already existing tobacco research literature. Specific salt compounds formed from nicotine and certain organic acids – such as nicotine benzoate, nicotine levulinate, and nicotine salicylate – indeed vaporize at those required lower temperatures. “And since nicotine salts do have lower pH levels than freebase nicotine, using them in e-liquids results in a smoother throat hit,” elaborated Balconi. Lastly, the improved nicotine absorption effectively means that a lower nicotine concentration in an e-liquid still provides the familiar satisfactory nicotine rush that heavy smokers require. It all comes together now, doesn’t it?

A salt for every need 

When we’re talking “nicotine salts”, it is in plural. The reason for that is, of course, that freebase nicotine can form chemical compounds – i.e. becoming a salt – with various substances. In other words, there is no one single nicotine salt, but there are many. For modern e-liquid manufacturing, five main nicotine salts have firmly established themselves, though. The differing benefits of these main nicotine salts are not yet fully defined and perceptions vary in consumer testing, but more research is in progress. Yet when drawing on already available data and consumer feedback, these five main nicotine salts indicate quite similar and only very subtle differences in the vaping experience. Alchem is supplying all of these salts under its NicSelect brand. Let’s take a quick look at them in turn: 

Nicotine Levulinate 

(as “NicSelect Velvet Salt”) 

Nicotine levulinate desensitizes the upper respiratory tract and enhances the binding of nicotine to neurons that ordinarily would be unresponsive to nicotine. Having a low pH, in this case a value of 4.4 ±0.5, it is well balanced in terms of smoothness and nicotine rush whilst having a minimal throat hit compared to other salts. 

“When a nicotine salt is used in an e-liquid instead of freebase nicotine, it will greatly improve the vaping experience.”
Anna Balconi - Alchem Europe

Nicotine Benzoate 

(as “NicSelect Smooth Salt”) 

In Alchem-conducted test panels, nicotine benzoate has been found to reduce, mask or neutralize the inherent taste of nicotine and causes less throat irritation. Its pH is slightly in the acidic range, around 6.2 ±0.5. Nicotine benzoate was one of the first nicotine salts to hit the mass market, helping create nicotine salts’ reputation for offering a very smooth vaping experience while providing a rapid and noticeable nicotine rush. However, Tom Xie of the SMOORE Research Center pointed out that while nicotine benzoate previously was “the nicotine salt most commonly used in e-liquids,” some European countries have “voluntarily” banned it in the meantime. “A number of vape brands have therefore started using non-benzoate e-liquids and in my opinion it is foreseeable that non-benzoates will become the mainstream trend in the future,” Xie said. 

Nicotine Ditartrate 

(as “NicSelect Rush Salt”) 

Having a rather low pH of 3.2 ±0.5 and a good absorption rate, nicotine ditartrate is neutral in taste, making it a popular choice for formulation with all types of carrier liquids and flavor combinations. It is commercialized extensively in smoking cessation products globally and is reported to provide the most rapid uptake and most notable nicotine rush. 

Nicotine Salicylate 

(as “NicSelect Chill Salt”) 

Regarded as one of the “more natural” acid salts because it is commonly also found in low concentrations in certain fruits, vegetables, herbs, spices, nuts, and teas, nicotine salicylate provides the smoothest vaping experience of all nicotine salts currently commercialized. It has a pH value of 5.5 ±0.5 and Alchem test panels reported it to provide a “coolness” to the vape. With little or no flavor changes reported while offering a very pronounced nicotine rush, it isn’t overbearing and has no harsh throat hit. 

Nicotine Lactate 

(as “NicSelect Silver Salt”) 

With lactates also being very common in dairy products as well as occurring in the human body, nicotine lactate is regarded as yet another one of the “more natural” nicotine salts. When used in e-liquids, it softens the nicotine taste and has a pH value of 4.0 ±0.5. Alchem test vapers reported nicotine lactate to have quite similar properties to the aforementioned nicotine salicylate, with a mid-range nicotine delivery and without a strong throat hit. 

The future is thoroughly salted 

With nicotine salts’ continued popularity growth, e-liquid manufacturers and vape houses have new possibilities at their fingertips to extend existing or launch new product lines, putting innovation back on track that was partially stalled when the EU’s TPD hit the industry. “Nicotine salts have given a huge opportunity to the vape sector and their use has spread rapidly, attracting more consumers with a better vape experience and convenience,” said Anna Balconi. However, freebase nicotine is not completely out of the picture. When used in higher wattage devices, it is still quite acceptable for most casual vapers. But it has nevertheless become very clear that tobacco smokers find consuming freebase nicotine e-liquids unsatisfactory, many among them switching back to tobacco products as a result. Nicotine salt e-liquids, on the other hand, help make the transition from tobacco smoking to vaping considerably more successful in most cases. SMOORE’s Tom Xie concurred. “Simply speaking, nicotine salts provide a far better vaping experience [than freebase nicotine] because they allow for the nicotine to be absorbed directly in the lungs,” he reiterated. “That in turn more closely simulates the sensation of smoking a real cigarette,” he concluded.