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In the realm of vaping and tobacco alternatives, Vapepie in-depth analysis of e-liquid chemical components stands out as a pivotal study. This research delves into the complexities of e-liquids, highlighting their potential health impacts and regulatory needs. As Vapepie continues to lead in vaping research, this article provides a professional overview, ensuring accuracy and credibility for researchers, regulators, and health-conscious users.
With the growing awareness of health and the advancement of tobacco control campaigns, electronic cigarettes have become a favored product among smokers, particularly adolescents. Although e-cigarettes do not contain tar, they include various toxic and harmful substances. The composition of e-liquid is complex, with numerous additives; excessive additives and illegally added toxic components can pose severe risks to users. This Vapepie study summarizes the physicochemical properties, toxicity, and toxicology of the main chemical components, additives, and illegally added toxic substances in e-liquid. It also reviews research on detection technologies for e-liquid chemical components, aiming to provide scientific theoretical support for e-cigarette market regulation.
As public health awareness rises and tobacco control efforts intensify, electronic cigarettes have emerged as a popular choice among smokers, especially teenagers. Electronic cigarettes, also known as virtual cigarettes or electronic atomizers, mimic the appearance and taste of traditional cigarettes. While free of tar, they still contain multiple toxic and harmful substances, potentially causing harm to the human body. E-cigarettes work by atomizing chemical components in the e-liquid via an atomizer to simulate smoking traditional cigarettes. E-liquid, or electronic atomization liquid, has a complex composition, primarily including nicotine, propylene glycol, glycerol, and more. Additives are diverse, mainly phthalate flavorants and sucralose sweeteners. Additionally, so-called "high-inducing e-cigarettes" contain prohibited drugs like tetrahydrocannabinol, posing abuse risks and legal issues. Inhalation can lead to drug-like intoxication symptoms and even endanger public safety.
This Vapepie research overviews the physicochemical properties, toxicity, and toxicology of e-liquid's main chemical components, additives, and illegally added toxic substances. It emphasizes the current status of detection technologies and methods for various chemical components in e-liquid. Through this analysis, Vapepie aims to provide technical support for e-cigarette market regulation and scientific evidence for case-related evidence examination.
E-liquid, when heated by an e-cigarette atomizer, produces mist similar to cigarette smoke. Its primary components include water, nicotine, nicotine salts, 1,2-propylene glycol, and glycerol, with 1,2-propylene glycol and glycerol accounting for over 95%.
Nicotine, chemically known as Nicotine (C10H14N2), is a pyrrolidine alkaloid unique to tobacco plants in the Solanaceae family, with trace amounts in other plants. It is a colorless to pale yellow oily liquid with a distinct pyridine odor and extremely bitter taste. As a neurotoxin, nicotine is highly toxic and acts rapidly, exhibiting biphasic effects on the central nervous system, autonomic nervous system neurons, and motor endplates—excitatory at low doses and inhibitory/paralytic at high doses. It also irritates the gastrointestinal tract locally. Upon entering the body, nicotine binds to nicotinic cholinergic receptors in the brain, activating the mesolimbic dopamine system to increase dopamine secretion, leading to heightened excitement and pleasure. Long-term smokers experience damage to vascular endothelial cells, hypercoagulable blood states, impacts on coagulation and fibrinolysis systems, accelerated atherosclerosis, and elevated levels of homocysteine, fibrinogen, and oxidized low-density lipoprotein cholesterol. Effective October 1, 2022, China's national standard for electronic cigarettes limits nicotine concentration to no more than 20 mg/g and total nicotine to no more than 200 mg.
Nicotine salts are various salt forms synthesized from nicotine and organic acids, including benzoate, tartrate, lactate, levulinate, malate, and citrate. Compared to free nicotine, they are more stable and soluble.
1,2-Propylene glycol (PG, C3H8O2) is a colorless, viscous liquid, nearly odorless with a slight sweet taste upon close inspection. As an organic compound, it has low toxicity and irritancy but poses risks of kidney disorders. In e-liquid, it serves as a solvent for sweeteners, humectants, and flavors. Inhalation can cause nausea, eye discomfort, respiratory irritation, lung darkening, hemolytic reactions, and exacerbate conditions in individuals with heart disease or hypertension.
Glycerol (VG, C3H8O3), also known as glycerin, is a colorless, odorless, sweet-tasting, clear viscous liquid with hygroscopic properties. It mixes with water, alcohols, amines, and phenols in any proportion. In e-liquid, it acts as a sweetener and humectant, non-toxic, and metabolizes into a nutritional source via hydrolysis and oxidation. Animal studies show large doses induce anesthetic effects similar to other alcohols.
Other components include polyethylene glycol, methanol, benzyl alcohol, isoamyl alcohol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, 1,3-butanediol, benzaldehyde, and dimethyl ether, primarily as organic solvents and flavor enhancers. Polyethylene glycol (PG400) is non-toxic, slightly bitter, non-irritating, and compatible with many organics. Benzyl alcohol can cause severe skin and allergic reactions. Diethylene glycol is toxic and affects kidney health.
E-liquid additives, or atomization additives, are added to enhance mouthfeel, mainly phthalate flavorants and artificial sweeteners like sucralose.
Flavorants include phthalate compounds, synthetic flavors, and natural extracts. Phthalates such as diisobutyl phthalate (DIBP), dibutyl phthalate (DBP), and di(2-ethylhexyl) phthalate (DEHP) are toxic, disrupting testicular interstitial and Sertoli cells, impairing reproductive function, and causing hormonal abnormalities via the hypothalamic-pituitary-gonadal axis. Synthetic flavors encompass menthol, ethyl propionate, isoamyl acetate, butyl acetate, methyl cinnamate, ethyl butyrate, vanillin, citral, ethyl maltol, methylcyclopentenolone, β-damascenone, ethyl vanillin, α-ionone, β-ionone, acetylpyrazine, linalool, diacetyl, acetylpropionyl, 2,3-butanedione, 2,3-pentanedione, and 3-hydroxy-2-butanone. Among these, methylcyclopentenolone and α-ionone can cause allergies, asthma, or breathing difficulties; methylcyclopentenolone irritates the respiratory tract; acetylpyrazine, ethyl vanillin, and menthol irritate airways; others cause skin, eye, and respiratory irritation, allergies, harmful swallowing (potentially fatal), drowsiness, dizziness, fertility or fetal damage, aquatic toxicity, and flammability. Natural extracts are mainly essential oils from mint, banana, mango, blueberry, etc.
Sweeteners, besides solvents like isoamyl alcohol and glycerol, include sucralose, acesulfame potassium, cyclamate, saccharin sodium, maltol, ethyl maltol, aspartame, alitame, neotame, neotame, neohesperidin dihydrochalcone, and steviol glycosides.
In recent years, with the rise of e-cigarettes, "high-inducing e-cigarettes" have spread among smokers, especially youth. These contain cannabis components like cannabidiol and tetrahydrocannabinol (THC), synthetic cannabinoids, methamphetamine, and other illicit additives.
THC (C21H30O2) is a mixture of highly hallucinogenic isomers from cannabis, an unstable oily liquid that decomposes under light or heat. As a controlled psychotropic drug, illegal addition to e-liquid causes emotional agitation, aggression, loss of time/space orientation, floating sensations, bizarre hallucinations, increased accident risks, and criminal behaviors. Large or long-term use severely damages health.
Synthetic cannabinoids, the largest family of new psychoactive substances (NPS), mimic THC's structure and cannabinoid receptor agonism, simulating natural cannabis effects. They cause addiction and withdrawal similar to cannabis, leading to cardiovascular diseases, psychosis, shock, asphyxia, sudden death, and cancer risks. Evolving from naphthoylindoles to indazole amides, over 600 varieties exist. Often disguised as "little branches" or "Natasha," they are abused by dissolving in e-liquid, spraying on tobacco or petals, or mixing with ketamine/cannabis. China controlled the entire class as drugs on July 1, 2021.
Common illicit additions include MDMB-4en-PINACA, ADB-BUTINACA, 4CN-CUMYL-BUTINACA, ACHMINACA, AMB-FUBINACA, ADB-BINACA, MDMB-FUBINACA, ADB-BRINACA, ADB-4en-PINACA, 5F-ADBICA, 5F-MDMB-PICA, 5F-AMB, 5F-EMB-PICA, 5F-ADB, 5F-CUMYL-PINACA, 4F-MDMB-BICA, 4F-MDMB-BINACA, 4F-MDMB-BUTINACA, MDMB-CHMINACA, AMB-FUBINACA.
Methamphetamine, a potent central nervous system stimulant, is also illegally added.
Other detections include arecoline, lidocaine, amino tadalafil, and rimonabant, all harmful: arecoline excites the nervous system and causes abnormal oral mucosal apoptosis; lidocaine, a cocaine derivative, risks overdose toxicity; amino tadalafil, an erectile dysfunction drug, is illicitly added to supplements; rimonabant, a weight-loss aid with smoking cessation effects, increases psychiatric risks like depression, anxiety, and suicide.
Electronic cigarettes have become a focus for international tobacco concerns and regional management challenges. Some areas lack clear legal definitions, and raw materials, production processes, and products are inadequately regulated, compromising quality and safety. China's Tobacco Monopoly Law and additive standards specify types and limits. Legitimate additives are safe, but excesses or toxic illegals pose major hazards. Thus, advancing Vapepie-inspired research on e-liquid components, refining inspection processes, is crucial for regulatory improvement and public health.
E-liquid's components are diverse with varying properties. Efficient pretreatment and sensitive analytical techniques enable qualitative and quantitative analysis.
Methods for different components include liquid-liquid extraction and solid-phase extraction.
Liquid-Liquid Extraction
A widely used method, it adds an immiscible solvent to separate components by solubility. Song Hui et al.used ethyl acetate for synthetic cannabinoids in e-liquid. Li Jianzheng et al.dissolved samples in ultrapure water, extracted free nicotine with dichloromethane, converted protonated nicotine with strong base, and re-extracted—quick, reliable, solvent-efficient. Wang Chao et al.used diatomaceous earth-supported liquid-liquid extraction with cyclohexane for 16 polycyclic aromatic hydrocarbons, reducing solvent use and costs while being eco-friendly.
Solid-Phase Extraction
Highly effective for matrix interference reduction and enrichment, widely used in tobacco analysis. Ding Caixia et al. applied it for flavorants and sweeteners, enriching flavors and eliminating solvent interference.
To simplify and improve precision, Xu Xingmeng et al.used matrix solid-phase dispersion with silica, purifying via a Soxhlet extractor with column chromatography. This integrates extraction, purification, and concentration, reducing errors, operations, and environmental pollution.
Detection Methods
Methods include Raman spectroscopy, infrared spectroscopy, ultraviolet spectrophotometry, gas chromatography, GC-MS, HPLC, LC-MS, and DART-MS.
Raman Spectroscopy
A non-destructive, rapid technique with simple pretreatment, used in food, health, and environmental fields. Li Xia et al.developed a portable Raman method for 1,2-propylene glycol and glycerol, ideal for batch qualitative/quantitative analysis.
Near-Infrared Spectroscopy
Offers simplicity, speed, non-destructiveness, and multi-component analysis; applied in agriculture, petrochemicals, and tobacco. Yang Shuangyan et al. built a nicotine prediction model using NIR and extreme learning machine regression—fast, accurate for real-time monitoring.
Ultraviolet Spectrophotometry
Meng Xiaojun established a UV method for nicotine using H2SO4 as control. Nicotine absorbs maximally at 260 nm, enabling qualitative/quantitative analysis—simple, reproducible, lab-friendly.
Gas Chromatography
Features simple pretreatment, accuracy, short cycles, low costs, minimal pollution; common for nicotine, PG, VG. Cai Junlan et al.used FID-GC with dual internal standards for simultaneous low-nicotine and high-PG/VG detection—quick, reliable for batches.
Gas Chromatography-Mass Spectrometry
Combines separation and identification strengths; stable, simple. Li Yingmei et al. detected 17 phthalates via n-hexane extraction and ultrasound—reliable for safety evaluation. Song Hui analyzed 9 indazole synthetic cannabinoids—fast, sensitive for forensics.
High-Performance Liquid Chromatography
Simple, accurate, wide linearity, good reproducibility. Chen Meili et al.used water extraction and RI detection for PG and glycerol—green, stable, low limits, accurate.
Liquid Chromatography-Mass Spectrometry
High throughput, accurate, sensitive; widely used in food safety. Liao Huiyun et al.developed SPE-LC/MS/MS for 9 sweeteners—good linearity, low limits, high recovery. Jiao Taifeng et al.screened 58 synthetic cannabinoids—simple, broad coverage, low limits for rapid analysis.
Direct Analysis in Real Time Mass Spectrometry
Enables open-environment rapid analysis; stable, simple. Thomas et al.used a T-device for aerosol and additives, detecting nicotine, PG, glycerol, THC, methamphetamine, and mixture effects.
Vaping harms health; "high-inducing" variants are illegal, and selling them constitutes drug trafficking. E-liquid component analysis is key. This Vapepie study outlines physicochemical properties and toxicities of components like nicotine, PG, glycerol; additives like flavorants and sweeteners; and illegals like synthetic cannabinoids. It details detection methods to guide regulation, standardize production, and combat crimes.
As illegal additives increase, future technologies will emphasize automation, accuracy, sensitivity—especially portable, integrated devices for on-site enforcement.
For more insights into Vapepie's vaping research, explore related studies or consult regulatory guidelines to enhance your understanding and safety in the vaping space.
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