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Flow Injection Analysis for Aluminium using 3-Hydroxy-4-Chloroflavone.

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Dev. Chem. Eng. Mineral Process., 11(5/6), pp. 437-444, 2003.
Flow Injection Analysis for Aluminium
using 3=Hydroxy=4'-Chloroflavone
Hiroshi Nishioka* and Tohru Nagahiro
Dept of Engineering Science, Faculty of Engineering, Himeji
Institute of Technology, 21 67 Shosha Himeji 671-2201, Japan
A flow injection system is described for the determination of aluminium. This
method is based on the formation of a fluorescent complex with 3-hydroxy-l'-
chloroflavone. The maximum wavelength of its excitation and emission spectra
are 397 and 455 nm, respectively. A 2 0 0 ~ 1aliquot of sample solution is
injected into a carrier (distilled water) which is pumped at 1.1 ml min-'. The
reagent solution is prepared by mixing the flavone ethanol solution ( I x ~ O M)
-~
and buffer solution (PH4) in the volume ratio of 5:l. The reagent solution is
also pumped at I . 1 ml min-I. Aluminium ion in the sample solution reacts with
fravone in the coil (0.5 mm i.d. x 3 m) to form afluorescent complex. A linear
relationship was observed between peak heights and aluminium
concentrations in the range of 2.4-100 ng mr'. The relative standard
deviation for five replicate injections is 0.9%. A routine sampling rate of 20
determinations per hour can be achieved by the proposed method.
Introduction
Aluminium is widely used in many industrial fields and it is desirable to
develop various analytical methods for aluminium detection. There are several
methods for the determination of aluminium in water, such as fluorometry [l31, spectrophotometry [4-71 and other methods [8, 91. The fluorometric
method is useful when using a reagent that gives strong fluorescence intensity
* Author for correspondence (nishioku@esci.eng-himeji-tech.ac.jp).
43 7
H.Nishioka and T.Nagahim
cs
1.1
Rs
1.1
S
I
-
:.....-..----.--..--1
* ,
L..
--..--...
'
1-455
nm
by forming a complex with aluminium. Recently, we synthesized several
derivatives of 3-hydroxyflavone (flavonol) and found that 3-hydroxy-4'chloroflavone forms a complex with aluminium to give stronger fluorescence
intensity than that of a flavonol-aluminium complex. In this work, we
synthesized 3-hydroxy-4'-chloroflavone, and studied its availability as a
reagent for the determination of aluminium by FIA.
Experimental Details
(i) Apparatus
A Hitachi Model 650-10s spectrofluorophotometer was used for recording
excitation and emission spectra. The detector used in the flow system was a
Hitachi Model F-1150 spectrofluorophotometer with a 40 pl flow cell. A
Nihon Seimitsu Kagalcu Model SP-D-2502U double plunger pump was used to
drive all flow streams. A Rheodyne Model 5020 sample injection valve and
PTFE mixing joint were also used. A Rikadenki Kogyo Model R-031 chart
recorder was used to record the peak heights. The manifold was built with 0.5
mm i.d. PTFE tubing and a Y-shaped connector. A schematic diagram of the
FIA system employed is shown in Figure 1.
(ii) Reagents
Aluminium solutions were prepared by diluting 1000 mg/l of standard solution
for atomic absorption spectrometry. All chemicals were of analytical-reagent
grade and distilled deionized water was used throughout. A procedure for the
(4'-chloroflavonol) is as follows. A
synthesis of 3-hydroxy-4'-chloroflavone
mixture of equimolar amounts of o-hydroxyacetophenone and 4chlorobenzaldehyde was stirred at 400 in alkaline methanol medium for 3
hoursand 2'-hydroxy-4-chlorochalconewas formed as an intermediate in the
438
Flow Injection Analysis for Aluminium using 3-Hydmp4'-Chlomflavone
p
3
0
I w
I
+
DC1
H
II
'
0
0
II
0
Figure 2. Synthesis of3-hydroxy-4 '-chloroflavone(4'-chloroflavonol).
solution. 3-hydroxy-4'-chloroflavonewas synthesized by the ring closure and
oxidation of this chalcone with alkaline hydrogen peroxide at 0°C. Figure 2 is
a schematic of this reaction.
Results and Discussion
(i) Fluorescent characteristics of several aluminium complexes
Under optimum conditions, the fluorometric characters of several flavonolaluminium complexes are summarized in Table 1, where the fluorescence
intensities are shown as relative values. The 4'-chloroflavonol gave the
highest fluorescence intensity in these complexes and no reagent blank
fluorescence was observed, so we chose 4'-chloroflavonol as a ligand for the
fluorometric determination of aluminium.
(ii) Preparation of reagent solution
The complex of aluminium and 4'-chloroflavonol was successfully formed in
the pH range of 3 to 5 , so we used buffer solution of pH 4 to prepare the
reagent solution. The solubility of 4'-chloroflavonol in water was very low,
and increasing the 4'-chloroflavonol solution seems to cause negative effects
such as an increase in reagent blank or a precipitation in the tubing. Therefore,
1.0 x lom4
M of 4'-chloroflavonol concentration was selected for this system.
439
H. Nishioka and T.Nagahim
When 100 ng d-'
of aluminium sample is injected, this reagent concentration
corresponds to 11-fold excess of 4'-chloroflavonol in molar ratio at the
reaction coil.
Table I . Fluorescence intensity of aluminium complexes with flavonol and its
derivatives.
Fla von01
Fluorescence
Flavonol
Fluorescence
intensity
derivatives
derivatives
1
Complex
Flavonol
4 '-methyl
4 '-ethyl
4'-isopropyl
4'-isobutyl
4 '-ethoxy
4'-propoxy
4 '-butoxy
4'-phenyl
65
19
100
29
71
21
40
12
38
Blank
4
8
23
6
13
8
38
12
23
Complex
4 '-phenoxy
4 '-c hloro
6-methy1
6-fluoro
3'-methyl
3'-hydroxy-4'methoxy
7-methoxy-4'methyl
1
Blank
2
88
19
10
0
2
2
0
25
21
2
2
12
100
I
(ili) Effect of manifold variables
The effects of pump flow rate, sample loop volume, reaction coil length and
its temperature on the fluorescence intensity were stpdied with the optimum
reagent condition.
The peak height depends on the residence time of the sample zone in the
system (on the flow rate and tube length). Although low flow rates gave
higher peak heights, they also caused lower sample throughput. Thus a flow
rate of 1.1 ml min-' for each channel was selected as the best compromise
between sensitivity and throughput in this system.
The effect of sample loop volume was studied with a pump flow rate of 1.1
ml min" and reaction coil length of 3 m. The sample volume was varied
between 50 and 250 p1. The peak heights linearly increased in proportion to
sample volume up to 250 p1. In general, a large sample volume sometimes
causes double peaks on recording chart. It means there is an excess of sample
volume over reagent volume. Thus a sample volume of 200 p1 was chosen for
further experiments.
Figure 3 shows the effect of reaction coil length on the fluorescence
intensity with other optimized manifold parameters. Short reaction coils gave
440
Flow Injection Analysisfor Aluminium using 3-Hydroxy-4'-Chlomjlavone
I
I
I
I
I
Figure 3. Effect of reaction coil length on peak height.
higher peak heights, but at a coil length of 1 m the peak height reproducibility
was poor. Thus the length chosen for the reaction coil was 3 m.
The effect of temperature on the formation of the complex was also studied
under the above conditions. As shown in Figure 4, high peaks were observed
in the range 40 to 5OOC. Above 5OoC, peak heights lowered with the rise in
temperature. It seems that these reductions indicate temperature quenching of
fluorescence caused by lack of cooling with the cooling coil placed at the back
of the reaction coil. These reductions will be recovered by using a cooling coil
longer than 1 m. However the longer the lengths of cooling coil, the lower the
sample throughput. Thus, we selected a reaction temperature of 45°C in this
system.
(iv) Calibration curve and precision
Under the optimum conditions described above, a series of standard solutions
of aluminium was injected into the manifold to test the linearity of the
a linear
calibration curve. For the concentration range 20-100 ng d-',
relationship between aluminium concentration and fluorescence intensity was
obtained with a correlation coefficient of 0.9989. The limit of quantification
was 2.4 ng ml-', which is calculated as the concentration equal to 10 times the
standard deviation of the background signal. The relative standard deviation
44 I
H.Nishioka and I: Nagahim
Figure 4. Effect of temperature.
was 0.9% for five replicate injections with 50 ng ml-’ of aluminium solution.
The sampling rate was about 20 samples per hour.
Tolerance ratio [Ion]/[Al]
Diverse ion
~~
100
50
10
5
Co(II), Ni(I1)
Cu(II), Mg(II), In(III), tungstate, molybdate
Cr(V1)
Sn(II), Fe(III), Ga(II1)
(v) Effect of diverse ions
The effect of diverse ions on the determination of aluminium was examined
under the above conditions. The results are given in Table 2. The tolerance
limit was defined as the concentration ratio of added species causing less than
5% relative error. It is necessary to remove or mask these ions before sample
injection if sample water contains them with over tolerance ratio.
442
Flow Injection Analysis for Aluminium using 3-Hydroxy-4'-Chloroflavone
Conclusions
The proposed method is a simple, rapid, semi-automatic and inexpensive
technique for the determination of trace amounts of aluminium as low as 2.4
ng ml-'. This FIA system will be available for on-line monitoring of
aluminium in water.
Nomenclature
cs
Carrier solution
Reagent solution
Pump
Sample injection valve
Reaction coil
Cooling coil
Detector
Recorder
Waste
RS
P
S
RC
cc
D
R
W
References
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[4] Miyada, M. and Taniguchi,
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[7] Sombra. L., Luconi. M., Femanda Silva, M., Olsina, A. and Fernandez, L. 2001.
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[S] Salomon, S., Giamarchi, P., le Bihan, A., Becker-Ross, H. and Heitmann, U. 2000.
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444
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