A simplified analytical method for determining metals in e-liquid
An analytical method for simultaneous determination of eight metals in mainstream cigarette smoke using inductively coupled plasma mass spectrometry (ICP-MS) was reported at the Tobacco Science Research Conference (TSRC) in 2009. The method does not require digestion during sample preparation. The method was modified for determination of 15 metals in e-liquid and reported at the 2017 CORESTA Smoke-Techno Joint Study Groups Meeting. In general, the sensitivity of the method to metals with a high ionization potential, such as arsenic and selenium, was influenced by the presence of organic components such as propylene glycol and glycerol, the so-called “matrix effect”. Under this modified method, the matrix effect was minimized by using calibration standards with methanol and an additional internal standard for the two metals, thereby improving the quantitation of the 15 metals. The complexity of these additional procedures and the need to increase the number of metals quantitated in an e-liquid sample, however, remained challenges to be solved. In this study, we used two approaches to simplify the procedure and quantitate more metals. The first approach was to optimize ICP-MS parameters instead of adding methanol to the calibration standards. The second approach was to optimize internal standards to increase the number of metals quantitated. We validated the two approaches with a verification test. Spiked e liquid samples and calibration standards were diluted with a nitric acid solution and analyzed by an ICP-MS instrument equipped with a collision/reaction cell. The calculated recovery rates were sufficient to quantitate more than 20 metals in an e liquid sample simultaneously. These two approaches contributed to simplifying the procedure and increasing the number of metals quantitated.