Effect of free-base and protonated nicotine on nicotine yield from electronic cigarettes with varying power and liquid vehicle

Soha Talih,Ahmad El-Hellani,Rola Salman,Rachel El-Hage,Nareg Karaoghlanian,Najat Saliba,Alan Shihadeh

doi:10.1038/s41598-020-73385-6

Soha Talih, Ahmad El-Hellani + Show 5 more

Open Access

https://doi.org/10.1038/s41598-020-73385-6

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Abstract

Nicotine in electronic cigarette (ECIG) liquids can exist in a free-base or protonated (or “salt”) form. Protonated nicotine is less aversive upon inhalation than free-base nicotine, and many ECIG manufacturers have begun marketing protonated nicotine products, often with high nicotine concentrations. Regulations intended to control ECIG nicotine delivery limit nicotine concentration but do not consider nicotine form. In this study, we systematically examined the effect of nicotine form on nicotine yield for varying powers and liquid vehicles. A Kanger Subox Mini-C tank ECIG (0.5 Ω) was used to generate aerosols at varying powers (5–45 W) from liquid solutions that contained either free-base or protonated nicotine at 15 mg/g concentration, with a liquid vehicle consisting of either propylene glycol (PG) or vegetable glycerin (VG), resulting in four different solutions (free-base/PG, free-base/VG, protonated/PG, and protonated/VG). Nicotine yield was quantified using gas chromatography-mass spectrometry. Nicotine yields were not influenced by nicotine form under any condition investigated. At each power level, PG-based liquids resulted in approximately double the nicotine yield of VG-based liquids. Nicotine concentrations in the aerosols matched those of the parent liquids for both the PG and VG conditions. Increasing power led to greater nicotine yield across all conditions. The amount of nicotine emitted by an ECIG is independent of whether the nicotine is free-base or protonated, however the liquid vehicle has a strong effect on yield. Regulations intended to limit nicotine emissions must consider not only nicotine concentration, but also liquid vehicle and device power.

Highlights

Nicotine in electronic cigarette (ECIG) liquids can exist in a free-base or protonated form
While ECIG nicotine yield has been shown to increase with propylene glycol (PG)/vegetable glycerin (VG) ratio and power[8,9], the influence of nicotine form on yield previously has not been examined directly; the data available to date indicate that for a given pH, nicotine yield is independent of the acid used in the liquid[10], and that the protonated to free-base ratio found in the ECIG aerosol matches that of the liquid[11,12]
Nicotine yield was not significantly associated with nicotine form (p = 0.67), whereas yield was strongly associated with power and propylene glycol to vegetable glycerin (PG/VG) ratio (p < 0.01)

Summary

Introduction

Nicotine in electronic cigarette (ECIG) liquids can exist in a free-base or protonated (or “salt”) form. While ECIG nicotine yield has been shown to increase with PG/VG ratio and power[8,9], the influence of nicotine form on yield previously has not been examined directly; the data available to date indicate that for a given pH, nicotine yield is independent of the acid used in the liquid[10], and that the protonated to free-base ratio found in the ECIG aerosol matches that of the liquid[11,12] This knowledge gap is salient because to date EU and proposed US regulations aiming to limit nicotine delivery focus exclusively on nicotine c oncentration[13], neglecting form, PG/VG ratio, and electrical power, among other factors. We examined the effects of free-base vs. protonated nicotine forms on nicotine yield and the amount of liquid aerosolized while varying electrical power and liquid vehicle

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