Berkeley Lab Researchers Shine a Light on Vaping Chemistry

In a first-of-its-kind study, scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have used specialized X-ray spectroscopy technology to analyze in exquisite detail the acid-base equilibria of additive-enhanced nicotine in simulated vaping aerosols.

Their findings provide a foundation for better public health understanding of how recent e-cigarette additives alter nicotine chemistry before delivery to the respiratory system, and how these chemical changes could ultimately affect nicotine uptake and users’ perceptions of vaping.

Electronic cigarettes emerged in the early 2000’s as basic ‘cig-a-likes’ that mimicked the shape of traditional cigarettes. They have since evolved into complex, battery-powered electronic devices with e-liquid chemistries fine-tuned to affect how nicotine is delivered, dosed, and experienced.

Recent e-cigarette additives like benzoic acid can change the acid-base chemistry of nicotine in the inhaled aerosol by adding a proton. The result is a smoother pull with less throat irritation, allowing users to more comfortably inhale higher doses of nicotine. In encouraging higher dosing, these additive-laced vaping products are viewed as fueling an epidemic of youth vaping.

“Understanding the aerosolized chemical species of nicotine in the presence of additives like benzoic acid is particularly important for determining its effects once it reaches the body’s respiratory tissues,” said Berkeley Lab senior scientist Hugo Destaillats, the study’s principal investigator. “Our study describes how much of the delivered nicotine is present in the protonated form in the aerosol particles, and how this speciation differs between the core and surface of particles.”

To gain such a rare, detailed glimpse into e-cigarette chemistry and determine how much protonated nicotine is delivered by vaping, researchers used technology unique to Berkeley Lab’s Advanced Light Source (ALS) facility – X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The ALS is a specialized particle accelerator that generates bright beams of X-ray light to probe a wide range of chemical properties.

Musahid Ahmed, senior scientist at the Chemical Sciences Division, added, “The combination of X-ray spectroscopy with aerosol chemistry, pioneered by our group at LBNL and ALS, has allowed us to better understand complex and dynamic chemical problems in nano-sized and microscopic particles.”

One of the most striking findings from X-ray analysis was that nicotine’s acid-base equilibria in water-based aerosols is very different from its well-known behavior in aqueous solution in the same pH range. Furthermore, the researchers found important differences in the degree of protonation of nicotine present at the surface, with respect to that in the core of the particles.

“A lower degree of protonation of nicotine present in particle surfaces can be attributed to reduced hydration of ionic species at the interface,” said co-author Xiaochen Tang, from Berkeley Lab’s Indoor Environment Group. “This effect was stronger in the presence of constituents such as propylene glycol and glycerol, which are always present in the formulation of vaping liquids.”

Because acid-base chemistry affects nicotine uptake and users' perceptions, results from this study can help better understand how nicotine is delivered to the tissues and fluids in the respiratory system. For example, these results can help formulate aerosols delivered to model systems in future in vitro and in vivo studies addressing nicotine deposition and uptake. Describing the role of acidifying additives is needed to support public health policy interventions.