1 Microwave method for extracting arsenic species: Ultra-pure water, 1% HNO3, 1%
HNO3 þ 1% H2O2 (Table 1). The CRM and 0.2000 g of Panax notoginseng were
weighed into 50 ml polypropylene centrifuge tubes and 10 ml of solutions was
added, respectively. Covered centrifuge tubes were allowed to stand overnight
at room temperature. All tubes were randomized, heated in a microwave
accelerated reaction system (CEM Microwave Technology Ltd, USA) using three
temperature steps: (1) maintained samples at 55C for 10 min; (2) at 75C for
10 min; (3) at 95C for 30 min. And each step ramped to temperature over
a 5 min period