Chemistry Reference
In-Depth Information
the calibrations obtained for the spectrophotometric measurement of standard iodide solutions, amplified
after microwave-assisted oxidation (calibration line: 0.0040
+
0.0666
μ
g ml
-1
) and classical oxidation
(0.0297
g ml
-1
) by using periodate along with the corresponding analytical characteristics found
following both procedures. It can be seen that the microwave-assisted procedure provides the better precision
and low blank value.
+
0.0527
μ
Comments
The microwave-assisted procedure described here is a fast and reproducible method for the
quantitative oxidation of iodide, which can be applied as a previous step requiring periodate oxidation. As
compared to the classical method of periodate oxidation, the use of microwave energy for activation of
amplification reaction has made the reaction not only shortening of time (4 min instead of 2 h) but also
consumption of less energy, closed reactor for amplification (24-fold) was effective for avoiding any
sample loss.
3.2.4.3
Use of naturally occurring reagents for extraction - spectrophotometric determination of iron
Today flow injection analysis (FIA) has become a very powerful analytical tool. By introducing FIA, not only
several-fold increase in the sensitivity could be achieved by coupling on-line between preconcentration and
detection techniques, but also eco-friendly and low-cost procedures can be improved based on the on-line
separation followed by analyte determination. The potential of flow systems to develop greener analytical
procedures, by replacement of toxic reagents, waste minimization, and in-line treatment and recycling has
been emphasized [32]. Gaining popularity, the Green Analytical Chemistry aims to explore the use of
alternative reagents or alternative synthetic methods that minimize the use of toxic chemicals. Thus a natural
guava (
Psidium guajava L.
, Myrtaceae family) extract has been investigated as an alternative natural indicator
for iron quantification by the flow injection (FI) technique.
Green laboratory proposal
[33]
Fresh guava leaves (10 g) were treated in 150 ml water (pH 7), diluted
hydrochloric acid (pH 4.8) or sodium acetate buffer (pH 4.8) in a blending machine for 5 min. Then the
suspension was filtered through filter paper (Whatman no. 1) and the filtrate was kept at room temperature
for further use. It was found that guava leaf extract is stable for at least 4 h, which is sufficient for a continuous
experiment using FI. Thus the extract was prepared daily before use.
Both Fe (II), Fe (III) solutions (10 and 100 ppm each) were prepared in water, HCl solution and acetate
buffer. Guava leaf extracts in the three media were mixed with iron solutions prepared in the matching
medium at the ratio of 1:1 (
v/v)
for example, 10 ml extract:10 ml iron solution. Guava leaf extract without iron
solution was used as the blank solution. Mixtures of the guava leaf extract and iron solution were scanned for
absorption spectra, measured against each medium in the visible region using a UV/Visible spectrophotometer.
Finally, it was set at 570 nm and connected to a computer to record the FIA program. The FI manifold with
two lines, where the reagent was injected into the stream of buffer that was later mixed with the stream of
sample solution, is depicted is Figure 3.11.
The typical analytical characteristics of the reverse FI method are as follows. It has much better sensitivity
(1 ppm) and low blank value in comparison to normal FI system. It has the linear calibration with R
2
=
0.9997
in the working range 1-10 ppm iron. Percent recoveries in tap water spiked with Fe(III) was 95-97
%
. Sample
throughput was 20 injections/h.
Comments
The striking aspect of this green method is that no sample treatment is needed for iron
concentrations at or below 30 ppm since Fe (III) and Fe (II) absorbances are similar, probably due to complete
reduction of Fe (III) by some chemicals like tannin naturally present in the guava leaves. Higher concentrations,
however, might be measured by adding a reducing agent such as hydroxylamine to convert Fe (III) to Fe (II).
