Chemical Science Division, Lawrence Berkeley National Laboratory, Berkeley, California94720, United States.
Energy Technologies Area, Lawrence Berkeley National Laboratory, Berkeley, California94720, United States.
J Phys Chem Lett. 2023 Feb 9;14(5):1279-1287. doi: 10.1021/acs.jpclett.2c03748. Epub 2023 Jan 31.
A new generation of electronic cigarettes is exacerbating the youth vaping epidemic by incorporating additives that increase the acidity of generated aerosols, which facilitate uptake of high nicotine levels. We need to better understand the chemical speciation of vaping aerosols to assess the impact of acidification. Here we used X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to probe the acid-base equilibria of nicotine in hydrated vaping aerosols. We show that, unlike the behavior observed in bulk water, nicotine in the core of aqueous particles was partially protonated when the pH of the nebulized solution was 10.4, with a fraction of free-base nicotine (α) of 0.34. Nicotine was further protonated by acidification with equimolar addition of benzoic acid (α = 0.17 at pH 6.2). By contrast, the degree of nicotine protonation at the particle surface was significantly lower, with 0.72 < α < 0.80 in the same pH range. The presence of propylene glycol and glycerol completely eliminated protonation of nicotine at the surface (α = 1) while not affecting significantly its acid-base equilibrium in the particle core. These results provide a better understanding of the role of acidifying additives in vaping aerosols, supporting public health policy interventions.
新一代电子烟通过添加能增加气溶胶酸度的添加剂来加剧青少年吸电子烟的流行，这使得高尼古丁水平更容易被吸收。我们需要更好地了解电子烟气溶胶的化学形态，以评估酸化的影响。在这里，我们使用 X 射线光电子能谱 (XPS) 和近边 X 射线吸收精细结构 (NEXAFS) 光谱来探测水合电子烟气溶胶中尼古丁的酸碱平衡。我们表明，与在体相水中观察到的行为不同，当雾化溶液的 pH 值为 10.4 时，水颗粒核心中的尼古丁部分质子化，游离碱基尼古丁 (α) 的分数为 0.34。用等摩尔苯甲酸酸化进一步质子化 (pH 6.2 时，α = 0.17)。相比之下，在相同的 pH 范围内，尼古丁在颗粒表面的质子化程度要低得多，0.72 < α < 0.80。丙二醇和甘油的存在完全消除了尼古丁在表面的质子化 (α = 1)，而对颗粒核心中尼古丁的酸碱平衡没有显著影响。这些结果提供了对酸化添加剂在电子烟气溶胶中作用的更好理解，支持了公共卫生政策干预。
