3.3. Effect of flow rate of sample solution
The flow rate of sample solution affects the retention of Tl(I)
on the nanoparticle as an adsorbent and it controls the time
of analysis. Thus the influence of flow rate of sample solution
on retention of Tl(I) ions in a range of 0.5–2.5 mL min1 under
the optimum conditions (pH, eluent, etc.) was studied via pass-ing 50 mL of sample solution through the microcolumn by a
peristaltic pump. We observed that quantitative recovery
(>95%) of Tl (I) was obtained up to a flow rate of
1.5 mL min1 and the recovery decreased when the flow rate
was greater than 1.5 mL min1 due to a decrease in the adsorption
kinetics of reaction at higher flow rate. Thus, a flow rate
of 1.5 mL min1 was employed for subsequent investigations.
3.4. Effect of sample volume
In order to investigate the possibility of achieving high levels of
enrichment factor, we examined the effect of sample volume on
recovery of Tl(I). To achieve to this goal, a series of sample
solution over the range of 25–200 mL containing a fixed quantity
of Tl(I) were processed based on the recommended procedure.
The results were exhibited in Fig. 4.
According to this figure, as shown, quantitative recovery
(>95%) of thallium was obtained for sample volumes of
6100 mL for Tl(I) ions. Thus, the adsorbed Tl(I) can be eluted
with 1.0 mL 1.0 mol L1 HCl, so the enrichment factor of 100
was achieved by this method.
3.5. Adsorption capacity
Adsorption capacity is one of the important parameters in
assessment of the adsorption capacity of different adsorbents,
since it suggests how much adsorbent is required to quantitatively
concentrate the analyte from a solution. The capacity
study method which is used was the one adapted from that recommended
by Maquieira et al. (1994). To determine the
adsorption capacity, 30 mL aliquots of sample solutions containing
the different Tl(I) concentrations (in the range of 0–
30 lg mL1) were adjusted to the appropriate pH with
0.1 mol L1 HCl or NaOH. Then 20 mg of TiO2 nanoparticles
was packed in microcolumn and the preconcentration procedure
described above was applied. The amount of Tl(I) adsorbed
at each concentration level was determined. The
profile of the adsorption isotherm for thallium was gained by
plotting the concentration (lg mL1) of Tl(I) solution versus
the milligrams of Tl(I) adsorbed per gram TiO2 nanoparticles,
and shown in Fig. 5. The result from the adsorption isotherm
shows that the adsorption capacity of TiO2 for Tl(I) was found
to be 25 mg g1.