Sample preparation
The glassware and polyethylene containers used for analysis were
washed with tap water, then soaked over night in 6N HNO3 solution
and rinsed several times with ultra pure water to eliminate
absorbance due to detergent13. The standard procedure described in
AOAC was followed for the preparation of samples for analysis of
heavy metals14. Accurately weighed (0.5 g) plant samples were
transferred in to a silica crucible and kept in a muffle furnace for
ashing at 450° C for 3 hours and then 5 ml of 6M HCl was added to
the crucible. Further, the crucible containing acid solution was kept
on a hot plate and digested to obtain a clean solution. The final
residue was dissolved in 0.1 M HNO3 solution and made upto 50 mL.
Standard solutions were prepared according to the Shimazdu Perkin
Elmer Pure Atomic Spectroscopy Standards guidelines (NIST
traceable CRM, Perkin Elmer Corporation, USA and Merck ‐
Germany). Working standard solutions were prepared by diluting
the stock solution with 0.1 M nitric acid for checking the linearity.