6. Evaluation of toxic heavy metal contamination
All 13 samples were analyzed for toxic heavy metal contamination.
Microwave-assisted acid digestion was used for all of the
samples, and the elemental contents and their infusions were
determined by FAAS and ICP-AES. Microwave digestion procedure
was applied under optimized conditions for dissolution
of herbal plants.
6.1. Acid digestion, FAAS and ICP-AES
In 400 ml cylinder, 300 ml of concentrated HCl and 100 ml of
concentrated HNO3 were added. The mixture was transferred
to a 1000 ml volumetric flask and the volume was made up with diH20. The mixture was inverted to mix and allowed to
stand.
Samples were dried at 70 C for 24 h after which they were
grinded in a Spex mill. Crucibles and caps were prepared by
washing in 10% HNO3 and muffled at 75 C for 2 h. Ground
samples of 0.5 g were placed in each crucible using a Mettler
(four-place) balance and placed in muffle furnace to bring
down to ashing temperature (45 C) slowly for 90 min and
ashed for 4 h. Crucibles were allowed to cool. Linear range
of concentrations was determined for the wavelength to be
used and an appropriate sample dilution scheme was devised.
Diluted extract was measured for metal content by an atomic
absorption spectrophotometry.
In the analyses of heavy metal contamination, the permissible
concentrations were set as follows; maximum of 0.15 mg/
kg for nickel (Ni), maximum of 0.2 mg/kg for lead (Pb), maximum
of 0.5 mg/kg for cadmium (Cd), maximum of 10 mg/kg
for copper (Cu), maximum of 50 mg/kg for zinc (Zn) and maximum
20 mg/kg for iron (Fe)