2.3. Digestion procedure
Approximately 200 mgof sample or certified referencematerialwas
placed directly into a microwave-closed vessel. Nine milliliter of 65%
(m/m) HNO3 and 3.0 mL of 37% (m/m) HCl were added to each vessel.
The microwave oven was operated according to the parameters
presented in Table 2, for the simultaneous digestion of nine vessels.
All experiments were performed in triplicate. The digests were put
into a 50 mL erlenmeyer and heated on a hot plate at 110 °C to near
dryness. After drying, the digested sample was diluted to 15 mL with
0.53 mol L−1 hydrochloric acid. In standard solutions and bauxite samples
were added 10 mg L−1 of internal standard. Gallium was determined
by ICP OES.