For the alkaline solubilization, about 10 mg of each sample were weighed out and solubilized with 10 mL of 0.1% (m v−1)TMAH, in a microwave oven (Model Multiwave Go, Anton Paar). The heating program consisted of 10 min at 100 °C andcooling to 55 °C during 12 min. The slurries were analyzed by GFAAS.