An alternative strategy for the determination of metals in the aerosol from electronic cigarettes
Methods for the determination of metals in mainstream cigarette smoke, in general, have limited flexibility and are susceptible to sporadic high levels of background contamination when applied to the collection of aerosol from electronic devices. To address these limitations, a procedure using pad collection principles and a standard linear smoking machine was developed for the analysis of 21 metals (Ag, Al, As, Au, Be, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Se, Sn, Sr, Ti, W, Zn, Zr) in aerosol from electronic cigarettes.
Multiple collection strategies were investigated with aerosol collection onto a quartz fiber filter providing the lowest, and most consistent, levels of background for most of the metals investigated. The capacity of the collection pad was determined to be approximately 400 mg accumulated aerosol mass. The sample preparation procedure was finalized to a simple extraction with 35 mL of 10% (v/v) ultrahigh purity nitric acid solution. The extract was analysed directly using ICP-MS.
The limits of quantification (LOQ) range from 2 ng/collection for Ag, to 59 ng/collection for Zn. The potential impact on quantification of the metals from the aerosol matrix was investigated by comparing slopes from calibrations built with standard solutions containing 10% methanol (for impact of carbon load), and various ratios of propylene glycol (PG) to glycerol (GLY), with calibrations of standards prepared in 10% HNO3. For most metals, matrix matched calibration slopes ranged of 80 to 100% of the slope from standards prepared in acid. However, metals such as As and Se, showed significant differences with slopes ranging from 39-56% and 30-43% respectively, dependent on the specific matrix. In cases where quantifiable levels of these metals are identified, a standard additions analysis using aliquots of the original extract would be required for accurate quantification.
For many metals, the background levels found in the collection pad were below the LOQ. However, quantifiable levels of Al, As, Cr, Fe, Mo, Ni, Pb, Sr, W, Zn and Zr were found. Collection of air blanks by drawing room air through the collection pads under the same puffing regime as test samples suggests metals from the environment are insignificant in comparison to the levels measured. The collection pads showed some lot-to-lot, as well as package-to-package variability within the same lot. However, pads within a single package showed very consistent background levels. Strategies for handling test sample results and background will be further discussed. This procedure can reduce the variability in the background which could mask the deliveries of metals in aerosol from electronic cigarettes.