Sample preparation and analysis
Plant
The plant edible part (leaves and stem) samples were washed thoroughly with tap water
before being rinsed with de-ionized water, then
dried at 70 °C in an oven. The samples were
ground into fi ne powder in an agate mortar. Plant
tissue was digested with concentrated HNO3 and
HClO4 (5:5, volume/volume; v/v). The extracted
samples were then analyzed using a fl ame-atomic
absorption spectrophotometer (Z-8200 Polarized
Zeeman; Hitachi, Ltd.; Tokyo, Japan).