About 0.5 g sample was weighed into dry, clean PTFE
digestion vessel. One milliliter of DDW was added first
and then supplied with appropriate digestion mixture:
HNO3/H2SO4, 2 + 1 (v/v) for wet digestion method 1 (WD1),
and HNO3/H2SO4/H2O2, 4+1+1 (v/v) for WD2. When the
initial reaction has subsided, vessel contents were gently mixed
and heated, first at lowtemperature (about 125 ◦C), then the temperature
was gradually increased until heavy evolution of fumes
ceases.