Quantitation of E-Cigarette Aerosol Mass in Liquid Impinger Solution Using the ¹³C of E-Liquids: Application for...

Liquid impingers, i.e., bubbling gaseous or aerosol samples through a liquid-based collection solution, are often used in electronic cigarette (e-cigarette) research to capture aerosols for metal analysis. However, a key limitation is the accurate quantitation of the mass of aerosol collected in the impinger solution for metal data normalization, which is necessary for comparison with prevaped e-liquid metal concentrations and for comparison across studies. To address this gap, we developed a novel approach to quantitate collected aerosol mass in a simple liquid impinger by leveraging the carbon-13 (¹³C) of aerosolized e-liquids, which enabled the parallel determination of aerosol mass and metal concentration by inductively coupled plasma mass spectrometry (ICP-MS). The method demonstrated low limits of detection and quantitation, excellent solution stability (≤4 months), and high accuracy and precision across spiked quality control samples, diverse e-liquid formulations, and multiple aerosol collection techniques (84.4-101% recovery with ≤4.6% relative percent deviation). Compared with an aerosol condensate collection method, the liquid impinger was equally effective at collecting metals, with metal concentrations on a mass-per-puff (ng/puff) basis within ∼7% for chromium (Cr), nickel (Ni), iron (Fe), copper (Cu), zinc (Zn), antimony (Sb), and lead (Pb). Aerosol metal concentrations on a mass-per-mass basis (ng/g) quantified using the ¹³C-derived aerosol mass from the liquid impinger were strongly correlated with (R² ≥ 0.97) but consistently greater than those from the condensate collection approach, due to differences in aerosol collection efficiency between methods. The liquid impinger enabled parallel aerosol mass and metal quantitation, offering a new approach for future e-cigarette aerosol studies, with potential application for investigations into future liquid impinger collection optimizations, e-liquid-to-aerosol metal transfer, and redox-sensitive speciation (e.g., Fe, Cu, Cr, Sb).