FTIR method for e-cigarette aerosol characterization
The global electronic cigarettes (e-cig) market and product variety is expected to continue growing over the next years. This growth is being accompanied with interest in methods to compare different products for many reasons, including potential future regulations for example. Thus to screen and assess a large portfolio of e-cigarettes and e-liquids there is a strong need for rapid aerosol characterization methods as an alternative to the classical, time consuming aerosol collection and analysis methods. For this purpose an on-line puff-by-puff liquid aerosol characterization method has been developed to quantify key e-cigarette aerosol constituents using Fourier Transformed Infrared (FTIR) spectroscopy.
The experimental setup is composed of three main parts: 1) a programmable single syringe aerosol generation pump, 2) a transfer section with a heated pump and heated tubes, and 3) a Gasmet™ FTIR spectrometer. For all investigations, aerosol was generated in accordance with the CORESTA recommended e-cigarette puffing protocol. The measured overall IR spectral response of the aerosol mixture was deconvoluted and matched online with reference calibration spectra in order to obtain the concentration in µg/L for water, propylene glycol, glycerol, and nicotine with a time resolution of 3 sample points per second.
In a first comparative study, aerosols of different liquid compositions were investigated using a commercially available e-cigarette. FTIR results were benchmarked against (i) liquid formulation (mass ratios) (ii) classical aerosol collection on filter followed by GC/Karl Fischer analysis of the filter extract (yields/50 puffs) (iii) e-cigarette device mass loss.
After calibrating the response of the system for the puff-to-puff aerosol dynamic FTIR results showed a very good agreement with the liquid formulation data and the analysis results from classical aerosol collection on filter. It is demonstrated that this method allows a simple and fast in depth product performance assessment on a puff-to-puff basis to investigate product yields including end of battery or end of liquid situations.