The recommended microwave-assisted acid digestions were carried out in TFM® closed vessels (ETHOS 1600,Milestone, Italy) in triplicate according to the following procedure: 1000mg of dried and ground material was accurately weighed, transferred to the vessels, and kept overnight (approximately 15 h) with 10 mL of 65% (v/v) HNO3 at room temperature in a fume hood