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Functional characterization of flavorings in electronic cigarette refill liquids by nuclear magnetic resonance spectroscopy

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Abstract

The chemical content of electronic cigarette liquids (e-liquids) was determined by NMR spectroscopy. The study aimed to quantify the abundance of propylene glycol, glycerol and nicotine and reconcile the functional types of non-exchangeable hydrogen of flavorings in e-liquids. Propylene glycol, glycerol, nicotine, menthol, vanillin and benzaldehyde were detected in e-liquids by 1D and 2D-NMR spectroscopy. Short- and long-range coupling of carbonyl, aryl and alkyl hydrogen was also observed by 2D 1H–1H and 1H–13C NMR. Propylene glycol and glycerol (from 30 : 70 to 65 : 35) accounted for more than 97% of e-liquids by mass with nicotine levels comparable to those reported by the manufacturer. E-liquids were classified into five clusters based on the relative distribution of non-exchangeable hydrogen types in flavorings. The mean relative abundance of flavorings ranged from 2.4 to 4.7% for the five clusters. Alkyl hydrogen was dominant in clusters II–V, representing 35–55% of non-exchangeable hydrogen, followed by saturated oxygenated hydrogen (32–33%). In cluster I, saturated oxygenated hydrogen was predominant. The highest abundance of aryl hydrogen was estimated for clusters I and IV, while carbonyls accounted for up to 1.5% of non-exchangeable hydrogen. Tobacco-flavored e-liquids had an average flavoring molar ratio of 1.8% with saturated oxygenated hydrogen being the predominant group with considerable quantities of aryl (6.8%) and carbonyl (1.5%) hydrogen atoms. Overall, this analysis allowed for the qualitative and quantitative determination of flavorings in e-liquids. This is needed to improve protocols aiming to determine the chemical composition of e-liquids and the feasibility of toxicological investigations.

Graphical abstract: Functional characterization of flavorings in electronic cigarette refill liquids by nuclear magnetic resonance spectroscopy

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Supplementary files

Article information


Submitted
03 Oct 2019
Accepted
09 Dec 2019
First published
11 Dec 2019

Anal. Methods, 2020, Advance Article
Article type
Paper

Functional characterization of flavorings in electronic cigarette refill liquids by nuclear magnetic resonance spectroscopy

O. M. Dada, M. G. Chalbot and I. G. Kavouras, Anal. Methods, 2020, Advance Article , DOI: 10.1039/C9AY02147G

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