Department of Chemistry Portland, State University Portland, Oregon 97207-0751, United States.
Department of Civil and Environmental Engineering Portland, State University Portland, Oregon 97207-0751, United States.
Chem Res Toxicol. 2020 Jul 20;33(7):1729-1735. doi: 10.1021/acs.chemrestox.0c00008. Epub 2020 May 19.
An important design aspect of electronic cigarettes ("e-cigarettes") is the nature of the acid/base chemistry in the e-liquid phase. E-liquids having formulations similar to those of early products are mixes of propylene glycol/glycerol (PG/GL) plus free-base (fb) nicotine and (usually) flavor chemicals that are either rather weak or non-acid/base actors in PG/GL. The fraction of nicotine in the fb form is denoted (α), with a possible range of 0 < (α) < 1. For e-liquids of an early design, (α) ≈ 1. Because e-cigarette aerosols high in fb nicotine are harsh upon inhalation, many commercial e-liquids now also contain variable levels of an acid additive (e.g., benzoic acid, levulinic acid, etc.) to protonate the nicotine and form dissolved "nicotine salts": (α) values significantly less than 1 are now common. A framework is developed for predicting α values in a given medium based on the following: (1) acid/nicotine ratios and (2) overall acid + nicotine protonation constant () values. This framework is required for understanding (1) e-liquid design in regard to how acid additives affect (α) values, and (2) why (α) values cannot, in general, be measured by any method that involves significant dilution with water.
电子烟（“电子烟”）的一个重要设计方面是电子液体相中的酸碱化学性质。具有类似于早期产品配方的电子液体是丙二醇/甘油（PG/GL）加游离碱（fb）尼古丁的混合物，并且（通常）是在 PG/GL 中为弱酸碱或非酸碱的香料化学品。以游离碱形式存在的尼古丁的分数表示为（α），其可能的范围为 0 <（α）< 1。对于早期设计的电子液体，（α）≈1。由于高 fb 尼古丁的电子烟气溶胶在吸入时很刺激，因此现在许多商业电子液体还含有可变水平的酸添加剂（例如苯甲酸，乙酰丙酸等）以使尼古丁质子化并形成溶解的“尼古丁盐”：（α）值现在通常明显小于 1。为了预测给定介质中的α值，提出了一个框架，该框架基于以下内容：（1）酸/尼古丁比和（2）总酸+尼古丁质子化常数（）值。这一框架对于理解（1）酸添加剂如何影响电子液体设计中的（α）值，以及（2）为什么（α）值通常不能通过任何涉及与水的大量稀释的方法来测量至关重要。
