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.