The results indicate the highest efficiency of extraction using 50% (v/v)
HCl. Other acids such as HNO3 and HClO4 did not show significant improvement
on Hg extractions. However, a previous study revealed that
a HNO3 solution presented higher efficiency to extract other metals
such as Pb, Cd and Cu in similar fertilizer samples . The efficiency of
HCl is probably due to the high affinity of chloride ions to mercury rather
than the oxidant power of nitric or perchloric acids. Next, the concentration
of HCl was varied in order to optimize the acid concentration keeping
5 min of sonication and 150 mg of sample. Once 50% (v/v) HCl resulted in
99% of recovery, lower concentrations of HCl were evaluated such as 30%
and 10% (v/v). The percentage recovery values were 100%±1 and 43%±
2, respectively.Hence, 30% (v/v) HCl (equivalent to 3.6 mol L−1)was used
for further studies of Hg extraction.