{"id":45256,"date":"2020-11-01T13:30:00","date_gmt":"2020-11-01T13:30:00","guid":{"rendered":"https:\/\/discover.restek.com\/uncategorized\/analysis-of-nicotine-and-impurities-in-electronic-cigarette-solutions-and-vapor\/"},"modified":"2025-12-10T20:57:37","modified_gmt":"2025-12-10T20:57:37","slug":"analysis-of-nicotine-and-impurities-in-electronic-cigarette-solutions-and-vapor","status":"publish","type":"post","link":"https:\/\/discover.restek.com\/ja\/application-notes\/ffan2127\/analysis-of-nicotine-and-impurities-in-electronic-cigarette-solutions-and-vapor","title":{"rendered":"Analysis of Nicotine and Impurities in Electronic Cigarette Solutions and Vapor"},"content":{"rendered":"\n

Abstract<\/h2>\n\n\n\n

Electronic cigarettes (e-cigarettes) are growing in popularity exponentially. Despite their ever-growing acceptance, relatively little work has been done to characterize their vapor. To date, the majority of e-cigarette research has focused on characterizing the solutions, which are ultimately vaporized for the end user to inhale. The current study focused on developing a complete analytical package for the quick and simple analysis of electronic cigarette solutions and vapor to determine nicotine content and impurity profiles. Rapid (<5 min) gas chromatography\u2013flame ionization detector (GC-FID) methods (using both helium and hydrogen carrier gas) were developed for the determination of nicotine content in e-cigarette solutions. In addition, a straightforward GC mass spectrometry (GC-MS) method was developed for the determination of impurities in e-cigarette liquids. Lastly, a simple sampling device was developed to draw e-cigarette vapor into a thermal desorption (TD) tube, which was then thermally extracted and analyzed via the same GC-MS method. This novel approach was able to provide detectable levels of volatile organic compounds (VOCs) and semivolatile organic compounds (SVOCs), which were not detected in the liquids, from a single 40 mL puff. All three of the methods may be done with one GC, two detectors, and one analytical column (Rtx-VMS), thereby reducing required resources and affording easy comparison of results.<\/p>\n\n\n\n

Introduction<\/h2>\n\n\n\n

Electronic cigarettes (e-cigarettes) do not burn tobacco, rather they produce an aerosol (without flame or smoke) from a battery-powered, metal heating element and liquid-containing cartridge [1]. The liquid typically consists of humectants (propylene glycol [1,2-propanediol] and\/or glycerin), flavorants, and nicotine [2]. When an e-cigarette\u2019s power source is activated, the heating element vaporizes the liquid to form a mist, which the end user then may inhale (often referred to as \u201cvape\u201d) [3]. The smoke-like vapor imitates tobacco smoke visually and replicates the burning sensation in the throat and lungs (often referred to as \u201cthroat hit\u201d). These similarities to tobacco smoke, combined with the same hand-to-mouth behaviors, have contributed to the rapid adaptation of electronic cigarettes [4-6]. Despite their increasing use on a global scale [3], relatively little is known about the e-cigarette chemical components. The majority of studies have focused primarily on the nicotine content and impurities (e.g., nitrosamines) of e-cigarette liquid (e-juice) [7]. More important, relatively little is known about the chemical composition of the vapor, which is ultimately what end users are exposed to [7, 8].<\/p>\n\n\n\n

Only a few researchers (e.g., Goniewicz et al. [7], Kosmider [9], and Schober et al. [8]) have attempted to characterize e-cigarette vapor by analyzing it for the presence of volatile organic compounds (VOCs), nitrosamines, heavy metals, and polycyclic aromatic hydrocarbons (PAHs); however, their study designs have been relatively complex and\/or required the use of a specialized smoking machine and\/or an array of specialized analytical instruments. Such requirements are often not practical for routine contract laboratory testing. The current study evaluates the nicotine content and impurities of several commercially available e-cigarettes and their respective solutions via simple and rapid GC-FID and GC-MS methods. In addition, the primary e-cigarette emissions were analyzed for VOCs and semivolatile organic compounds (SVOCs) via a simple and novel technique that pairs thermal desorption (TD) with GC-MS. Results, analytical techniques, obstacles, and solutions are discussed.<\/p>\n\n\n\n

Experimental<\/h2>\n\n\n\n

Electronic Cigarettes and Liquids<\/h3>\n\n\n\n

Four commercially available electronic cigarettes (Table I) were chosen from the \u201cBest E-Cigarettes of 2014,\u201d which is a top 10 list of e-cigarettes as viewed by \u201cexperts and users\u201d [10]. It is important to note that these four chosen e-cigarettes also routinely appeared on other web-based review sites as \u201ctop 10\u201d performers. In addition, these four brands were readily obtained from local stores. All four e-cigarettes were \u201c1st generation\u201d cigarettes (i.e., generally mimicking the size and look of regular cigarettes) [11] and, with the exception of vendor D, were disposable. In addition to the e-cigarettes, their respective e-liquids (i.e., same brand, flavor, and nicotine content) were obtained.<\/p>\n\n\n\n

Vendors A, B, and C indicated their claimed nicotine percentage was based on wt\/wt analysis. Vendor D indicated their labeled value was based on vol\/vol analysis; however, one side of the D refill solution bottle denoted 1,000 mg of nicotine, which is in keeping with a wt\/wt analysis (which appears to be the industry standard) or a wt\/vol analysis. Therefore, it was not entirely clear how vendor D determined their nicotine concentrations. Upon receipt, 1 mL of each e-cigarette solution was pipetted with a calibrated syringe onto a calibrated scale to determine the density of each solution. Measured densities were later used to convert wt\/wt label claims to wt\/vol values for direct comparison to the analytically determined wt\/vol values using the following equation:<\/p>\n\n\n\n

\"decorative\"<\/figure>\n\n\n\n

Table I:<\/strong> Characteristics of Electronic Cigarettes and Liquids<\/p>\n\n\n

Vendor<\/strong><\/th>Claimed Nicotine % (wt \/wt)<\/strong><\/th>Style<\/strong><\/th>Measured Density (g\/mL)<\/strong><\/th><\/tr><\/thead>
A<\/td>1.8 (18 mg\/1,000 mg)<\/td>Classic Tobacco<\/td>1.1179<\/td><\/tr>
B<\/td>1.2 (12 mg\/1,000 mg)<\/td>Classic Tobacco<\/td>1.1843<\/td><\/tr>
C<\/td>1.2 (12 mg\/1,000 mg)<\/td>Menthol<\/td>1.2006<\/td><\/tr>
D<\/td> 1.8 (18 mL\/1,000 mL)*<\/td>Classic Tobacco<\/td>1.1271<\/td><\/tr>
*One label on the solution refill bottle indicated the % nicotine was based on % vol\/vol; however, the other side of the bottle denoted 1,000 mg, which is in keeping with wt\/wt analysis.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n

Nicotine<\/h3>\n\n\n\n

The following system was used to analyze electronic cigarette e-liquid nicotine concentrations: an Agilent 7890A GC equipped with an Agilent FID. An Rtx-VMS column was chosen as the analytical column based on its unique ability to separate volatile compounds. The GC-FID parameters for both helium and hydrogen carrier gases are presented in Table II. The nicotine levels of the e-cigarette solutions were determined by calibrating the GC-FID with a National Institute of Standards and Technology (NIST) traceable nicotine standard (cat.# 34085). The 1,000 \u00b5g\/mL nicotine standard was serially diluted with methylene chloride to generate a 7-point external calibration curve (Table III). Although not shown, a United States (U.S.) Environmental Protection Agency (EPA) Method 8260 internal standard (cat.# 30074) was found to be suitable for the current work.<\/p>\n\n\n\n

All electronic cigarette solutions were diluted with methylene chloride by one hundred fold. This dilution was carried out for the following reasons: 1) Initial work with the e-cigarette solutions indicated the liquids were relatively viscous in nature. This viscosity resulted in the formation of air bubbles in the autosampler syringe. A 100:1 dilution remedied any viscosity issues. 2) The e-cigarette solutions chosen for this study appeared to have nicotine concentrations of ~15\u201325 mg\/mL, which was outside the concentration range of the calibration curve (Table III). A 100:1 dilution resulted in nicotine levels that fell between the upper and lower limits of the calibration curve. It is important to note that methylene chloride was chosen as the diluent instead of methanol because the methanol solvent peak coeluted with the ethanol (one of the major constituents of e-cigarette solutions) peak.<\/p>\n\n\n\n

Table II:<\/strong> Analytical system and parameters utilized for quantifying the nicotine content of electronic cigarette liquids.<\/p>\n\n\n

\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Agilent 7890A GC-FID<\/strong><\/td>\n<\/tr>\n
Column<\/strong><\/td>\nRtx-VMS, 30 m, 0.25 mm ID, 1.40 \u00b5m (cat.# 19915)<\/td>\n<\/tr>\n
Injection<\/strong><\/td>\nDiluted (100:1) electronic cigarette liquid<\/td>\n<\/tr>\n
Inj. Vol.<\/td>\n1.0 \u00b5L split (200:1)<\/td>\n<\/tr>\n
Liner<\/td>\nRestek Premium Precision liner w\/wool (cat.# 23305)<\/td>\n<\/tr>\n
Inj. Temp.<\/td>\n250 \u00b0C<\/td>\n<\/tr>\n
Septum Purge Flow<\/td>\n3 mL\/min<\/td>\n<\/tr>\n
Detector<\/strong><\/td>\nFID @ 250 \u00b0C<\/td>\n<\/tr>\n
Carrier Gas<\/strong><\/td>\nHe, constant flow<\/td>\nH2<\/sub>, constant flow*<\/td>\nH2<\/sub>, constant flow*<\/td>\n<\/tr>\n
Flow Rate<\/td>\n2.0 mL\/min<\/td>\n2.50 mL\/min<\/td>\n2.50 mL\/min<\/td>\n<\/tr>\n
Linear Velocity<\/td>\n44.4 cm\/sec<\/td>\n67.2 cm\/sec<\/td>\n67.2 cm\/sec<\/td>\n<\/tr>\n
Oven<\/strong><\/td>\n100 \u00b0C to 260 \u00b0C at 35 \u00b0C\/min
(hold 0.25 min)<\/td>\n		100 \u00b0C to 260 \u00b0C at 54 \u00b0C\/min
(hold 0.15 min)<\/td>\n		100 \u00b0C to 240 \u00b0C at 35 \u00b0C\/min<\/td>\n<\/tr>\n
*Requires a fast ramping oven\u00a0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/figure>\n\n\n

Table III:<\/strong> External nicotine calibration curve for quantifying the nicotine content of electronic cigarette liquids.<\/p>\n\n\n\n

1.00 mg\/mL Nicotine Standard (cat.# 34085)<\/strong><\/td><\/tr>
Level<\/strong><\/td>\u00b5L of Previous Level<\/strong><\/td>\u00b5L of Methylene Chloride<\/strong><\/td>Total Volume (\u00b5L)<\/strong><\/td>Concentration (mg\/mL)<\/strong><\/td><\/tr>
1<\/td>NA<\/td>NA<\/td>NA<\/td>1.00<\/td><\/tr>
2<\/td>100<\/td>100<\/td>200<\/td>0.500<\/td><\/tr>
3<\/td>100<\/td>100<\/td>200<\/td>0.250<\/td><\/tr>
4<\/td>100<\/td>100<\/td>200<\/td>0.125<\/td><\/tr>
5<\/td>100<\/td>100<\/td>200<\/td>0.063<\/td><\/tr>
6<\/td>100<\/td>100<\/td>200<\/td>0.031<\/td><\/tr>
7<\/td>100<\/td>100<\/td>200<\/td>0.016<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Impurities<\/h3>\n\n\n\n

The following analytical system was used for the qualitative determination of any impurities found in the electronic cigarette solutions: an Agilent 7890B GC coupled with an Agilent 5977A MS detector. The GC-MS parameters are presented in Table IV. This analysis also utilized the Rtx-VMS column based on its proven performance for volatile compounds.<\/p>\n\n\n\n

Table IV:<\/strong> Analytical system and parameters utilized for determination of electronic cigarette solution impurities.<\/p>\n\n\n\n

Agilent 7890<\/strong>B\/5977A GC-MS Parameters<\/strong><\/td><\/tr>
Column<\/strong><\/td>Rtx-VMS, 30 m, 0.25 mm ID, 1.40 \u00b5m (cat.# 19915)<\/td><\/tr>
Injection<\/strong><\/td>Diluted (2:1) electronic cigarette liquid<\/td><\/tr>
Inj. Vol.<\/td>1.0 \u00b5L split (10:1)<\/td><\/tr>
Liner<\/td>Restek Premium 4 mm Precision liner w\/wool (cat.# 23305)<\/td><\/tr>
Inj. Temp.<\/td>250 \u00b0C<\/td><\/tr>
Purge Flow<\/td>3 mL\/min<\/td><\/tr>
Oven<\/strong><\/td>35 \u00b0C (hold 1 min) to 250 \u00b0C at 11 \u00b0C\/min (hold 4 min)<\/td><\/tr>
Carrier Gas<\/strong><\/td>He, constant flow<\/td><\/tr>
Flow Rate<\/td>2.0 mL\/min<\/td><\/tr>
Linear Velocity<\/td>51.15 cm\/sec<\/td><\/tr>
Detector<\/strong><\/td>MS<\/td><\/tr>
Mode<\/td>Scan<\/td><\/tr>
Transfer Line Temp.<\/td>250 \u00b0C<\/td><\/tr>
Analyzer Type<\/td>Single quadrupole<\/td><\/tr>
Source Temp.<\/td>230 \u00b0C<\/td><\/tr>
Quad Temp.<\/td>150 \u00b0C<\/td><\/tr>
Electron Energy<\/td>70 eV<\/td><\/tr>
Tune Type<\/td>BFB<\/td><\/tr>
Ionization Mode<\/td>EI<\/td><\/tr>
Acquisition Range<\/td>15 \u2013 550 amu<\/td><\/tr>
Rate<\/td>5.2 scans\/sec<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Vapor<\/h3>\n\n\n\n

Electronic cigarette vapor was analyzed for nicotine and impurities by trapping the vapor on thermal desorption tubes. Goniewicz et al. and other researchers have used smoking machines (e.g., Teague TE-2, Borgwaldt RM20S) to generate and collect e-cigarette aerosols; however, access to such an apparatus was not available for this study [7]. Therefore, in order to provide reproducible and quantitative results, a simple sampling device (Figure 1) was adapted from a 50 mL gas-tight syringe (cat.# 24761). The syringe was used to draw 40 mL of vapor in ~4 seconds from the e-cigarettes across a stainless steel thermal desorption tube packed with Tenax TA, Carbograph TD, and Carboxen 1003 (unconditioned [cat.# 26469] or conditioned [cat.# 26470]). This tube was chosen based on the optimized combination of three sorbents to screen for VOCs in the C2-3<\/sub>\u00a0range up to SVOCs in the C30-32<\/sub>\u00a0range. Although this method was manual, a ~4-second puff was utilized, as suggested based on Farsalinos et al.\u2019s observations on e-cigarette topography [12]. In addition to the single puff sample, a 10-puff sample was also taken in order to mimic a smoking regime. This sample was taken by manually drawing ten 4-second puffs separated by 10-second intervals between puffs. The desorption tube was then transferred to the following analytical system for determining the VOCs and SVOCs directly emitted from an e-cigarette: a Markes UNITY thermal desorption system paired with an Agilent 7890B GC coupled to an Agilent 5977A MS detector. The UNITY system and GC-MS parameters are presented in Table V and Table IV, respectively.<\/p>\n\n\n\n

The vapor concentrations of selected VOCs were calculated from a 5-point calibration curve generated by analyzing a series of volumes of a 10.0 ppbv primary standard (Table VI). The 10.0 ppbv primary standard was generated by injecting 180 mL of a 1.00 ppmv 75 component TO-15 + NJ mix (cat.# 34396) and 180 mL of a 1.00 ppmv ozone precursor mixture\/PAMS (cat.# 34420) into an evacuated 6-liter SilcoCan air monitoring canister (cat.# 27309) and pressurizing the canister to 30 psig with 50% RH nitrogen. Ochiai et al. [13] determined 50% RH to be optimal for stability. The standard was allowed to age for 7 days.<\/p>\n\n\n

Figure 1:<\/strong>\u00a0Gas-tight syringe sampling apparatus for quantitatively drawing electronic cigarette vapor into a thermal desorption tube.<\/div>
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