New Analytical Method for Quantifying Flavoring Chemicals of Potential Respiratory Health Risk Concerns in e-Cigarette Liquids.

Michelle K Page,Maciej L Goniewicz

doi:10.3389/fchem.2021.763940

Abstract

Numerous flavoring chemicals are added to e-cigarette liquids to create various flavors. Flavorings provide sensory experience to users and increase product appeal; however, concerns have been raised about their potential inhalation toxicity. Estimating potential health risk of inhaling these chemicals has been challenging since little is known about their actual concentrations in e-cigarette products. To date, a limited number of analytical methods exist to measure the concentrations of flavoring chemicals in e-cigarette products. We have developed an analytical method that accurately and precisely measures the concentrations of 20 flavoring chemicals of potential inhalation risk concerns: 2,3,5-trimethylpyrazine, acetoin, benzaldehyde, benzyl alcohol, butanoic acid, dl-limonene, ethyl maltol, ethyl salicylate, ethyl vanillin, eucalyptol, eugenol, furaneol, isovanillin, l-menthol, maltol, methyl salicylate, pulegone, trans-cinnamaldehyde, triacetin, and vanillin. Calibration and QC solutions were prepared in 50:50 propylene glycol (PG):vegetable glycerin (VG) and 5% H2O and flavoring concentrations ranging from 0.02 to 10.00 mg/ml. Samples of commercial e-cigarette liquids, calibration and QC solutions were combined with 30 µL of an internal standard mix (benzene-d6, pyridine-d5, chlorobenzene-d5, naphthalene-d8 and acenaphthene-d10; 1 mg/ml each) and were diluted 100-fold into methanol. Analysis was performed on an Agilent 7890B/7250 GC/Q-TOF using a DB-624UI column (30 m x 0.25 mmID x 1.4 μm film thickness), with a total runtime of 13.5 min. Calibration curves were fit using a weighted quadratic model and correlations of determination (r 2) values exceeded 0.990 for all chemicals. Bias and precision tests yielded values less than 20% and lower limits of quantitation (LLOQ) ranged from 0.02 to 0.63 mg/ml. Over 200 commercially available products, purchased or collected from adult e-cigarette users and spanning a range of flavor categories, were evaluated with this method. Concentrations of pulegone, a suspected carcinogen, varied from below limit of quantitation (BLOQ) to 0.32 mg/ml, while acetoin and vanillin, known precursors to more cytotoxic byproducts, ranged from BLOQ to 1.52 mg/ml and from BLOQ to 16.22 mg/ml, respectively. This method features a wide dynamic working range and allows for a rapid routine analysis of flavoring additives in commercial e-cigarette liquids.

Highlights

Flavoring chemicals are a main constituent of e-cigarette liquids and help impart either a characteristic flavor or contribute to the overall sensory experience of e-cigarette users
Initial findings suggest a link between inhalation toxicity of e-cigarettes and flavorings (Bahl et al, 2012; Leigh et al, 2016), while more recent in vitro studies have demonstrated specific chemicals such as cinnamaldehyde, benzaldehyde, ethyl vanillin, ethyl maltol and vanillin to be highly cytotoxic to respiratory cells (Behar et al, 2018; Hua et al, 2019; Rickard et al, 2021), as well as disruptive to normal cellular and immune function (Gerloff et al, 2017; Hickman et al, 2019)
Selected flavoring chemicals have been shown to form free radicals when heated in e-cigarette devices (Muthumalage et al, 2017; Bitzer et al, 2018), as well as known carcinogens such as benzene (Pankow et al, 2017), while others react with solvents used in e-cigarette liquids to form more highly cytotoxic acetal byproducts (Erythropel et al, 2019; Jabba et al, 2020)

Summary

Introduction

Flavoring chemicals are a main constituent of e-cigarette liquids and help impart either a characteristic flavor or contribute to the overall sensory experience of e-cigarette users (vapers). Initial findings suggest a link between inhalation toxicity of e-cigarettes and flavorings (Bahl et al, 2012; Leigh et al, 2016), while more recent in vitro studies have demonstrated specific chemicals such as cinnamaldehyde, benzaldehyde, ethyl vanillin, ethyl maltol and vanillin to be highly cytotoxic to respiratory cells (Behar et al, 2018; Hua et al, 2019; Rickard et al, 2021), as well as disruptive to normal cellular and immune function (Gerloff et al, 2017; Hickman et al, 2019). Ethyl vanillin and vanillin have been revealed to contain potentially addictive properties (Truman et al, 2019)

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