2.1. Reagents and solutions
All chemicals used were of analytical grade. Double-deionized
water was used for preparing the solutions and for all dilutions.
All stock solutions of metals (1000 or 100 mg L1) were prepared
from the nitrate salts of metals. Plant digests were prepared using
HNO3 (Merck, Germany). A certified reference material (GBW
07604 Poplar Leaves obtained from National Institute of Standards
and Technology, Beijing, China) was used to verify the accuracy of
the results of analyses.