Abstract
In the last few years, electronic cigarette has quickly increased. In evaluating their safety, and in view of upcoming guidelines, toxic heavy metals are the most potential to be monitored in the liquids of electronic cigarette (e-liquids). A sensitive analytical method using magnetic-graphene oxide extractor and inductively coupled plasma with optical emission spectroscopy (ICP-OES) was developed and validated to measure the levels of seven heavy metals in twenty five e-liquids from a local brand. Extraction of heavy metals by magnetic-graphene oxide had concentrated the level of metals and reduced the significant matrix effect generated from other e-liquid constituents. Regardless the lack of reference materials for e-liquids, the developed method demonstrated high linearity, precision, and allowed the quantification of low levels of heavy metals with quantification limit < 85 µg/L for Ni, Hg, Cd and Co. For the examined e-liquids, analysis indicated that the results were not normally distributed and presence of many outliers, hence, median value was more convenient than average value to evaluate the existence of heavy metals in the samples. The highest level of metals in unused e-liquids was reported for Cu, Cr, and Ni with average values of 2.51, 5.64 and 8.60 µg/g, respectively. Upon vaping, the level of Ni and Cu were increased by 2 and 37 folds, respectively, in the remaining liquid mainly due to contact with the device coil. Although there are no local or international standards on the quality of e-liquids, the proposed analytical method is transposable for official laboratories responsible for the quality of regular and electronic cigarettes.