Stock solutions of Cu(II),
Pb(II), Cr(III), Cd(II), Ni(II), Zn(II), Co(II) and Mn(II) were prepared
by dissolving an appropriate amount of analytical reagent grade
metal nitrate-salt in milli-Q water. For Fe(III) and Al(III) stock standard
solution were prepared from FeCl3 and AlCl3, respectively