For the heavy metals determination, leaves, stems, and flowers of Stevia rebaudiana plants of each weighed approximately 0.5 grams into a Teflon digestion vessel, to which was added exactly 7 ml high purity concentrated 65% of nitric acid (HNO3) and 1 ml high purity concentrated 30% of
hydrogen peroxide (H2O2). The vessels were then capped and fitted into rotor segments and inserted into the microwave digestion system. The samples were radiated for 20 min. Upon cooling, the vessels were uncapped and solutions transferred into 50 ml volumetric flasks.