Ags. Prado et C. Airoldi, Adsorption, preconcentration and separation of cations on silica gel chemically modified with the herbicide 2,4-dichlorophenoxyacetic acid, ANALYT CHIM, 432(2), 2001, pp. 201-211
The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), chemically anchored o
n a silica gel surface, has been used for Cu(II), Ni(II), Zn(II) and Cd(II)
adsorption from aqueous and ethanolic solutions at room temperature. The s
eries of adsorption isotherms were adjusted to a modified Langmuir equation
from data obtained by suspending the solid with MCl2 solutions (M = Cu, Ni
, Zn and Cd), which gave the maximum number of moles adsorbed as 0.44, 0.32
, 0.27 and 0.14 mmol g-l in water and 0.75, 0.52, 0.47 and 0.38 mmol g(-1)
in ethanol for Cu, Ni, Zn, Cd, respectively. The retention of cations from
aqueous solution was null at pH less than or equal to 3, however, the adsor
ption increased above this value up to pH 7. The maximum retention capacity
followed the sequence Cu > Ni > Zn > Cd in both solvents and presented a n
on-linear correlation with enthalpy of hydration and also with charge/radiu
s of each cation. The modified silica was applied for preconcentration and
quantification of trace level metal ions present in water and ethanol sampl
es. The immobilized surface was also used as a separation column for these
four cations. Column resolution was determined fbr all cations as the abili
ty of this surface to separate metal ions, determined as Rs(Cd-Zn) = 0.54,
RSCd-Ni = 0.64, Rs(Cd-Cu) = 1.62, Rs(Zn-Ni) = 0.28, Rs(Zn-Cu) = 1.26 and Rs
(Ni-Cu) = 0.68. (C) 2001 Elsevier Science B.V. All rights reserved.