Chemistry Reference
In-Depth Information
O
HO
C
C
N
NN
C
N
•
HO
C
H
OIV
Scheme 3.2
Anchoring of imidazole 4,5-dicarboxylic acid moiety onto DVB polystyrene matrix.
Comments
The work shows a comparative study between the two radiation grafted chitosan derivatives -
cross-linked chitosan (CRC) and cross-linked chitosan after hydrolysis (CRCH). The polymers can be
effective for the preconcentration and separation of uranium from different matrices. Evidently, the method
of biosorption is simple, eco-friendly and could be effective for the determination of trace amounts of uranium.
3.2.2.3
Green speciation of vanadium using a solid phase exchanger
Metal speciation is currently very important from the perspective of environmental, biological, geological
and medical applications. Vanadium is a real challenge in the field of speciation. This is because of its
complex chemistry and also this element has been proved to be essential after the discovery of its insulin
like properties [16]. Different forms of vanadium like V
2
O
5
, vanadates as vanadium (V) species and
vanadyl as vanadium (IV) are of different physiological action and toxicity. Hence differentiation and
quantification of vanadium in these two oxidation states are important. Co-precipitation followed by
instrumental analysis is the common method for speciation of vanadium but it is tedious, time consuming
and applicable to higher concentrations. Solvent extraction has also been used for the preconcentration
and separation of vanadium but due to excess solvent requirement, the use of such technique is restricted.
On the other hand, solid phase extraction could be a method of choice for preconcentration of vanadium
species at very low level.
Green laboratory proposal
[17]
The use of chelating resin has been popular with the introduction of
chelating group like imidazole 4,5-dicarboxylic acid anchored by -N
N- into the polystyrene -DVB matrix
(Scheme 3.2) and its application to the preconcentration and separation of vanadium species from natural
water. A glass column of 130 mm × 10 mm was used for the present work. Air dried resin (1 g) was immersed
in deionized water for 24 h and allowed to swell. The column was packed with swollen beads of the resin. The
bed volume of the column was 2 ml. The sorption and recovery characteristics for V (IV) and V (V) were
thoroughly examined under the flow rate of 0.5 ml min
-1
. The sorbed V (IV) and V (V) were eluted by 0.1 mol
l
-1
malonic acid solution and 0.15 mol l
-1
NaOH solution respectively. The samples of natural water were
filtered using 0.45
=
m Millipore membrane filter. Taking 500 ml of each sample, the pH was adjusted to 3 and
passed through the column at a flow rate of 0.5 ml min
-1
. After elution using the proposed method (10 ml of
eluent was used in each portion) the concentration of vanadium was measured in the final solution. The
results of vanadium speciation in different samples are shown in Figure 3.6.
μ
Comments
The speciation study of vanadium in natural water can be effectively carried out using solid
phase extractor containing imidazole 4,5-dicarboxylic acid as the ligating site. Both V (IV) and V (V) are
sorbed at pH 3 and thereby eluted with 0.1M malonic acid for V (IV) and 0.15 M NaOH for V (V). Therefore,
