## Materials and Methods
### Aerosol Sample and Pretreatment Method for EC Aerosol  
For analysis of the aerosol generated using EC, a filter is used for collection of the aerosol [45]. The analysis method for the EC aerosol used the tobacco analysis method of ISO, WHO, and CORESTA N\({}^{\circ}\) 75 [26; 30]. To compare the adsorption capacity of TSNAs on each filter media, CFP (44 mm \(\Phi\)) and QW were prepared [16]. Note that, for this comparative test, a dilution factor in the range of 20 to 100 was chosen to minimize the analytical interference of LC-MS/MS due to the large amount of PG and VG (e.g., >80%) in EC liquid solutions, and to maximize the detection capacity for the TSNAs. The amount of aerosol that is generated per puff and the consumption rate of EC solution were measured by the mass change tracking (MCT) method [46]. The dilution factor can be computed, as follows:  
\[\text{Dilution Factor}=\text{Amount of extraction solution (mL)/Amount of aerosol}\] \[\text{generated by EC smoke automatic sampling device (mL)}\]  
The CFP used as a sampling filter for tobacco mainstream smoke in the ISO, WHO, and CORESTA N\({}^{\circ}\) 75 methods has a large diameter (44 mm) and 20 mL of extraction solution is generally required to extract TSNAs that are captured on CFP. In contrast, the QW filter is prepared manually by packing 15 mg of QW into a quartz tube (6.35 mm \(\times\) 90 mm), and is commonly used for GC-MS-based thermal desorption analysis of indoor air and odor samples [47]. For the evaluation of RR for the CFP, spiked samples were prepared at three concentrations of 500, 1250, and 2500 ng mL\({}^{-1}\) for the extraction of TSNAs captured on CFP using 10 mL extraction solution (dilution factor: \(\sim\)330). In the case of the QW filter, relatively low concentration levels of 100, 500, and 1000 ng mL\({}^{-1}\) of spiked samples were prepared while considering the need for a small amount (1.8 mL) of extraction solution (dilution factor: \(\sim\)60) as compared to CFP. Spiked samples that were collected using two types of sampling filters (CFP and QW) after solvent extraction were prepared at concentrations of 2, 5, and 10 ng mL\({}^{-1}\) to allow quantitative recovery analysis using a LC-MS/MS system.  
An automatic sampling device for EC smoke designed by Chemtekins Co. (Sungnam, Korea) was used to precisely control the rate of generation of EC aerosol [41]. The EC device filled with either a spiked sample or a commercial E-liquid was placed in the EC smoke automatic sampling device for the production of aerosols. For triplicate analysis, the vaped sample was collected onto three individual filters. Sampling of the aerosol onto each filter of CFP and QW was conducted at a sampling (purging) velocity of 1 L min\({}^{-1}\), with the following puff conditions: puff interval, 10 s; puff duration, 2 s; and, the number of puffs, 10. The CFP-collected aerosol samples (A-CFP) were extracted with 10 mL of AA and ultrasonicated for 30 min. Extracted solution (2 mL) was then filtered through a syringe filter (0.45 \(\upmu\)m, PTFE) and transferred to a 2 mL vial. In the case of sampling vapor onto QW filter (A-QW), 1.5 g (\(\sim\)1.8 mL) of AA was filtered directly through a QW filter and transferred to a 2 mL vial. The aerosol sample collected on the QW filter according to the puff conditions selected in this study (as described above) is approximately 30 mg. Hence, the dilution factor of the extraction solvent is about 50. The extraction solution was transferred to a 2 mL amber vial for convenience of final analysis and a 1-\(\upmu\)L sample from the two types of filtered extract solution was analyzed by LC-MS/MS. A schematic diagram of analysis of the aerosol sample for both types of filter is shown in Supplementary Figure S1 online.