Generation of Substantially Metal-Reduced but Aldehyde-Rich Aerosol for E-Cigarette Toxicity Studies

Summary

Here, we establish that aerosolization of a commercial e-liquid by a pneumatic atomizer at 200 °C provides a metal-reduced aerosol that has aldehyde levels comparable to those found in real-world e-cigarette aerosol.

Abstract

When e-liquid is aerosolized in an e-cigarette for inhalation by the user, the aerosol becomes contaminated by a mixture of toxicants, including metals and aldehydes. A method to generate e-cigarette aerosol with high aldehyde but low metal content is lacking, yet is needed to untangle the potential independent effects versus toxicological interactions of aldehyde and metal exposure from e-cigarette aerosol mixtures.

The objective of this study was to establish a method for generating aldehyde-rich aerosols from e-liquids that lack, however, the large metal contamination typically found in e-cigarette aerosol. To aerosolize e-liquid at temperatures that promote aldehyde formation (up to 200 °C), a pneumatic atomizer was externally heated. Both a pure propylene glycol/vegetable glycerin (PG/VG) mixture and a commercial e-liquid were aerosolized. Aerosols were analyzed for known e-cigarette-associated toxicants, including 11 aldehydes using liquid chromatography-tandem mass spectrometry and 9 metals (Cr, Cu, Fe, Mn, Ni, Pb, Sr, V, Zn) using inductively-coupled plasma mass spectrometry.

Aldehyde levels in aerosols from the pneumatic atomizer only reached those in a real-world e-cigarette aerosol if the commercial e-liquid was aerosolized at 200 °C. Metal levels in the aerosols from the pneumatic atomizer were then at least 8 times lower than in e-cigarette aerosol from a "Mod" device operated at 50 W. Cu, Ni, and Pb levels were particularly low across all aerosol samples, with some levels below the method detection limit (MDL).

Aerosolization of a commercial e-liquid by a pneumatic atomizer at 200 °C produces aerosol that is low in metal levels (particularly Ni, Cu, Pb), but has aldehyde levels comparable to those found in a real-world e-cigarette aerosol.

Introduction

In the US, e-cigarettes are the most commonly used tobacco product among youth; in 2024, 5.9% of students reported using e-cigarettes¹. This is a public health concern because e-cigarette aerosols, which are inhaled by e-cigarette users, contain a broad range of toxic chemicals that, upon inhalation, can have various adverse health effects². Some toxic chemicals in aerosols may not only emanate from the original e-liquid formulation but also be introduced during device use. For instance, metals leach from the metallic heating coil used to aerosolize the e-liquid through the process of dissolution and evaporation into the....

Protocol

Setting up the pneumatic atomizer
All materials used in the study are listed in the Table of Materials file. To generate simulated e-cigarette aerosol without using a metallic heating coil that releases metals, we used a commercial pneumatic atomizer. To achieve the high temperatures needed to promote aldehyde formation, we heated the pneumatic atomizer as a whole by wrapping heating tape around it. To that end, we loosened the two screws, which secure the actual aerosol unit to its stand, such that the heating tape could be guided through the resultant gap instead of wrapping it around the stand. The temperature of the pneumatic ....

Results

Exploring the conditions that promote aldehyde formation
Aerosols were generated in four phases. At first, we used the pneumatic atomizer to generate aerosols from the PG/VG solution at 50 °C and 100 °C, and we used the "Mod" e-cigarette to generate aerosol from the commercial e-liquid at 30 W and 50 W operating power. As determined by LC-MS/MS, total aldehyde levels were much lower in the PG/VG aerosols than in real-world e-cigarette aerosol (Figure 2A).

Discussion

The total aldehyde concentration (11 aldehydes) of aerosols we generated with the pneumatic atomizer from commercial e-liquid at a temperature of 200 °C was on the order of those measured in aerosols from a Mod device operated at 30 or 50 W. In particular, acrolein occurred at the high levels observed in the real-world e-cigarette aerosols. However, levels of formaldehyde did not match those observed in the e-cigarette aerosols. Altogether, the levels of aldehydes reported in our study, which range from low ng/g to .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Agilent 8900 ICPMS	Agilent	https://www.agilent.com/en/product/atomic-spectroscopy/inductively-coupled-plasma-mass-spectrometry-icp-ms/icp-ms-instruments/8900-triple-quadrupole-icp-ms?
Aldehyde/Ketone-DNPH standards	Supelco	ERA-028
Analyst software	Sciex	version 1.6.2
C18 column	Kinetex	https://www.phenomenex.com/part?partNo=00D-4475-AN	1.7 µm
Collision-type atomizer	TSI	Model 3076
Commercial e-liquid	Beyondvape, Baldwin Park, California, US	Pale Whale Vixen’s Kiss	purchased with a 6% nicotine content
Electrochemical sensor	Sensirion	SFA30
Extreme-temperature PTFE tubing	McMaster-Carr	5239K12	Extreme-temperature hard plastic tubing for chemicals, semi-clear Teflon® PTFE Plastic without Stripe, 3/16" ID, 1/4" OD,
Filtered air supply	TSI	Model 3074B
Heating tape	BriskHeat	TBIH051-020LD	Dual Element, Cloth Insulated Heat Tape, 2 inch x 1/2 inch, 156 Watts
High-temperature silicone tubing	Quickun	Pure Silicone Tubing, 1/16" ID, 1/8" OD
Mars 6	CEM	https://cem.com/mars-6
Microcontroller board	Arduino	Arduino Uno Rev3
Mod e-cigarette	Eleaf Electronics Co., Ltd., Shenzhen City, China	iStick Pico Plus, Melo 4S Tank, EC-A 0.3 Ω coil
Multiquant	Sciex	version 3.0.3
NexION 350S ICPMS	Perkin Elmer	NexION 350S
Nitric acid	Fisher Chemical	Optima	Ultra Trace Elemental Analysis grade
Platinum resistance temperature detector	Adafruit	PT1000
Qtrao 6500 LC-MS/MS System	Sciex	https://sciex.com/products/mass-spectrometers/qtrap-systems/qtrap-6500-system	Tandem mass spectrometer
Shimadzu LC	Shimadzu	https://www.shimadzu.com/an/products/liquid-chromatography/index.html