Synthesis and spectrophotometric determination of acidity constants of 2,3,4,6′-tetrahydroxy-3′-sulfoazobenzene and their use in determination of aluminum

Article abstract of DOI:10.3906/kim-0908-212

A novel azo derivative, 2,3,4,6′-tetrahydroxy-3′- sulfoazobenzene (THSA), was synthesized by using pyrogallol. The acid dissociation constants, or K^α values, of THSA were determined by the UV-visible spectroscopic technique. The protonation and

Full text of DOI:10.3906/kim-0908-212

Turk J Chem
35 (2011) , 291 – 305.
¨
˙
c
ꢀ TUBITAK
doi:10.3906/kim-0908-212
Synthesis and spectrophotometric determination of
acidity constants of
2,3,4,6ꢀ -tetrahydroxy-3ꢀ-sulfoazobenzene and their use in
determination of aluminum
1
1,∗
1
¨
¨ ˘
˙
˙
Tufan GURAY , Cemil OGRETIR , Tevfik GEDIKBEY ,
2
¨
˙
˙
Abu Ali HUSEYINLI
1Department of Chemistry, Faculty of Arts and Sciences, Eski¸sehir Osmangazi University,
Me¸selik 26480, Eski¸sehir-TURKEY
e-mail: cogretir@ogu.edu.tr
2Baku State University, Faculty of Chemistry, Baku 1148, AZERBAIJAN
Received 2008.2010
A novel azo derivative, 2,3,4,6ꢀ -tetrahydroxy-3ꢀ -sulfoazobenzene (THSA), was synthesized by using
pyrogallol. The acid dissociation constants, or Ka values, of THSA were determined by the UV-visible
spectroscopic technique. The protonation and deprotonation behaviors of the title molecule were studied
from the super basic to the super acid region (i.e. 10 N NaOH to 98% H2 SO4), including the pH region. A
selective and sensitive UV-visible spectrophotometric method was devised for determination of aluminum by
using this ligand. The developed method was successfully applied to an alunite mineral and to pharmaceutical
preparations for the determination of aluminum.
Key Words: Azo dye, acidity constants, aluminum, spectrophotometric determination
Introduction
Azo compounds are still a very important class of chemical compounds receiving much attention in scientific
research due to their chromophoric properties and fine staining qualities. These compounds have been commonly
used in both industry and analytical chemistry.1,2 In particular, 2,2ꢀ -dihydroxyazo compounds are well known
∗Corresponding author
291

¨
Synthesis and spectrophotometric determination of..., T. GURAY, et al.,
for their applications in analytical chemistry as chromogenic indicators.3−5 They are also being used for the
spectrophotometric determination of metal ions.6−10
Recently, tetrahydroxyazobenzene derivatives have started to be used in spectrophotometric determina-
tion of aluminum.9,10 These reagents enhance the stability of the formed band with the aluminum because of
the high electron density between the –OH groups’ ortho to azo group and the nitrogen atom of the azo group.
Most of the commonly used reagents for the determination of aluminum in the literature do not have
high sensitivity11 or require some surfactants for the enhancement of selectivity and sensitivity. 12,13
During the last 20 years, many investigators have focused on the toxicity of aluminum to living systems.14,15
Furthermore, aluminum is widely used as an antiperspirant in both cosmetic and pharmaceutical products. Sci-
entists are currently investigating suggestions of a link between the use of deodorants and both breast cancer
and Alzheimer’s disease.16−18
Commonly used analytical techniques for the determination of aluminum at trace levels are fluorimetry,19
atomic absorption spectroscopy (AAS),20 emission spectroscopy (AES),21 gas chromatography,22 and induc-
tively coupled plasma atomic emission spectrometry (ICP-AES).23
The knowledge of the pKa value of a substance is essential for various investigations in pharmacology and
physiology, for industrial purposes, in structural, environmental, preparative, and analytical studies, and so on.
Hence, we have determined the acidity constants of THSA by the spectrophotometric method. Spectrometry is
an ideal method24 when a substance is not soluble enough for potentiometry or when its acidity constant value
is particularly low or high (i.e. less than 2 or greater than 11).
In the present work, we have synthesized a novel THSA (Scheme 1). We are now reporting on the
determination of the acidity, which is expressed as acidity constants, or pKa values. We also report on the
usage of this reagent in the spectrophotometric determination of aluminum in artificial mixtures, alunite mineral,
and pharmaceutical preparations.
OH
OH
HCl + NaNO2
0 oC
NH2
N
N Cl
HO3S
HO3S
OH
HO
OH
HO
OH
OH
pH=3
+
N
N
OH
OH
N
N Cl
HO3S
Scheme 1. Synthesis of THSA.
HO3S
292

¨
Synthesis and spectrophotometric determination of..., T. GURAY, et al.,
Experimental
Instrumentation
The spectrophotometric measurements were carried out using a Unicam 2-UV Spectrometer Double Beam UV-
Visible spectrophotometer with a 1.00-cm quartz cell. The pH measurements were taken using an Orion 720A
pH meter.
Materials
The THSA was synthesized as in the literature.8 A stock solution of THSA was prepared by dissolving 0.1631
g of THSA in 500 mL of deionized water. The solution was stabilized for 1 month.
KOH, H2 SO4 , HCl, CH3 COOH, CH3 COONa, NaOH, KH2 PO4 , Na2 CO3 , NaHCO3 , NaCl, and
standard buffer solutions were obtained from Merck and were not purified further.
Acid solutions were prepared with H2 SO4 (w/w, 0.0049%-98% H2 SO4) in water.25 The CO2 -free
NaOH solutions were prepared with NaOH pellets (1-16.4 mol L−1) in water.26 Buffer solutions were prepared
using Perrin’s descriptions.27 The potentiometric measurements were performed by measuring the hydrogen ion
concentration under nitrogen atmosphere at 25
0.1 M using NaCl.
0.1 ◦ C, and ionic strengths of the media were maintained at
An alunite sample was obtained from S¸aphane, Ku¨tahya, Turkey. It was crushed, powdered, and sieved
through a 150-μm sieve, and samples were collected. The chemical composition of the alunite as determined
by XRF analysis was 43.47% silica, 27.12% alumina (14.386% aluminum), 23.50% sulfur trioxide, and 5.50%
potassium oxide as the major constituents, along with 0.41% of other compounds as impurities.28
r
ꢀ
A commercial preparation of oxethazaine [Mucaine
suspension containing 291 mg of aluminum hydrox-
˙
ide (100.656 mg of aluminum) in 5 mL] was obtained from Wyeth (Istanbul, Turkey), a commercial preparation
r
ꢀ
of dihydroxyaluminum sodium carbonate (DASC) [Kompensan
tablet containing 340 mg of DASC (54.970
˙
mg of aluminum) in 1 tablet (1 g)] was obtained from Pfizer (Istanbul, Turkey), and aluminum solution (ICP
1000 mg L−1 , Merck) was used as a stock solution. All solutions were prepared by diluting appropriate volumes
of the stock solution.
Synthesis of THSA
The THSA was synthesized using a recommended method from the literature.8 In a 3-necked, 250-mL flask was
placed 4.725 g (0.025 mol) of 2-aminophenol-4-sulfonic acid, dissolved by the addition of 5 mL of HCl (d = 1.19
g mL−1) and 50 mL of water. The mixture was stirred mechanically in an ice-water bath until its temperature
dropped to 0 ◦ C. Meanwhile, 1.725 g (0.025 mol) of NaNO2 salt was dissolved in 5 mL of water and added
dropwise to the flask at 0 ◦ C within 30 min. After completion of the addition, the mixture was stirred for 2 h.
The degree of diazotization was checked with starch paper. The excess NaNO2 was removed by the addition
of urea crystals, and 3.2 g (0.0255 mol) of pyrogallol was dissolved separately in 20 mL of water in a 3-necked,
25-mL flask for the azotization reaction. The pH of the solution was adjusted to 3 with HCl. The mixture
was cooled to 0 ◦ C in an ice bath, and a mixture containing diazonium salt was added to it within 30 min
293

¨
Synthesis and spectrophotometric determination of..., T. GURAY, et al.,
(Scheme 1). The final mixture was stirred with a mechanical stirrer for 2 h. The mixture was transferred to
a 250-mL beaker, and after the addition of 5 mL of concentrated HCl, it was kept on the bench for 1 night.
The crude product was chloride salt. The precipitate formed was filtered off with a Bu¨chner funnel, air-dried,
recrystallized from ethanol twice, and kept in a desiccator. The purity of the ligand was checked with thin
layer chromatography. The yield of the reaction with regard to pyrogallol was 47.8%, decomposed at >200 ◦ C.
Elemental analysis for C12 H10 O7 N2 S: Found (%) C 44.04, H 2.95, N 8.10; Calculated (%) C 44.17, H 3.09,
N 8.59. Moreover, the ultraviolet spectrum, infrared spectrum, 1 H-NMR, and 13 C-NMR were also applied for
structure elucidation.
Spectrophotometric determination of acidity constants of THSA
The general procedure was applied as follows: a stock solution of the compound under investigation was prepared
by dissolving about 10-20 mg of the compound in water in a volumetric flask. Aliquots (1 mL) of this solution
were transferred to 10-mL volumetric flasks and diluted to the mark with buffers of various pH values. The
pH was measured before and after addition of the new solution. The optical density of each solution was then
measured in 1-cm cells, against solvent blanks, using a constant temperature cell holder Unicam UV2 UV-Vis
scanning spectrometer thermostated at 25
0.1 ◦ C. The wavelength was chosen such that the fully protonated
form of the substrate had a much greater or a much smaller extinction coefficient than the neutral form. The
analytical wavelengths, the half-protonation values, and the UV absorption maximum are shown in Tables 1
and 2.
This method depends on the direct determination of the ratio of the concentration of molecular species,
that is, the neutral molecules corresponding to the ionized species in a series of nonabsorbing buffer solutions
for which pH values are either known or measured.24,29 For a weak base B, which ionizes by simple proton
addition, the Ho , H , or pH values at half-protonation were measured during the course of the present work using
the UV-Vis spectrophotometric method of Johnson et al.30 This method takes into account any effect of the
medium on the wavelength of the maximum UV absorption and the corresponding extinction coefficient. This
effect is particularly significant at high acidities. The protonation of a weak base can be defined as follows:25
HX + SH ꢀ X− + SH2+,
(1)
where SH is the solvent.
Calculations of half-protonation values were carried out as follows: the sigmoid curve of optical density
or the extinction coefficients at the analytical wavelength (OD, λ) were first obtained (Figure 1). The optical
density of the fully protonated molecule (ODca , optical density of conjugated acid) and the pure free base
(ODfb , optical density of free base) at an acidity were then calculated by linear extrapolation of the arms of
the curve. The following equation, Eq. (2), gives the ionization ratio in which the ODobs (the observed optical
density) is in turn converted into molar extinction, εobs , using Beer’s law of OD = ε.b.c (b= cell width, cm;
c = concentration, mol L−1):
I = (HX)/(X−) = (ODobs − ODfb)/(ODca − ODobs) = (εobs − εfb)/(εca − εobs).
(2)
294

¨
Synthesis and spectrophotometric determination of..., T. GURAY, et al.,
295

¨
Synthesis and spectrophotometric determination of..., T. GURAY, et al.,
The linear plot of log I against Ho or pH, using the values -1.0 < log I < 1.0, had slope m, yielding a
half-protonation value of H1/2 or pH1/2 at log I = 0 (Figure 1). The pKa values were calculated by using Eq.
(3):
pKa = H1/2 + logI,
(3)
which can mathematically be expressed as a straight line (y = mx + n) with a slope of m, thus becoming Eq.
(4).
pKa = m · H1/2 + logI
(4)
(5)
Since at the half-protonation point, log I will be equal to 0, we end up with Eq. (5):
pKa = m · H1/2
.
As the half-protonation value is equal to pKa in the pH region, pKa is equal to the H1/2 value of 6.10.
30000
1.5
25000
20000
15000
10000
5000
0
1
0.5
0
pH
3
4
5
6
7
8
-0.5
-1
-1.5
-2
0
2
4
6
8
10
12
pH
-2.5
a
b
Figure 1. a) The sigmoid curve pH-ε469 nm plot. b) The log I−pH plot for THSA for the first protonation (R2
0.99).
=
General procedure for determination of aluminum
An aluminum solution (5 × 10−4 mol L−1) was transferred into a 25-mL calibrated flask. THSA (2 mL of
1 × 10−3 mol L−1) was then added to this solution, and the colored solution was diluted with appropriate
solutions of pH 1-11. The final concentrations of aluminum and THSA in the reaction mixture were 2 × 10−5
mol L−1 and 8 × 10−5 mol L−1 , respectively. The absorbances were measured by using either a blank reagent
or water at 480 nm.
296

¨
Synthesis and spectrophotometric determination of..., T. GURAY, et al.,
Result and discussion
The protonation and deprotonation behaviors of the THSA
UV-Vis spectroscopic data related to the deprotonation and protonation processes of THSA are depicted in
Tables 1 and 2. Possible protonation patterns are shown in Schemes 2, 3, 4, and 5. The obtained results will
be discussed using the scale of Scheme 6.
OH
HO
OH
OH
OH
HO
OH
OH
α
α
β
β
H2O
N N
A
N N
A
B
B
O3S
HO3S
Scheme 2. Ionization of sulfonate group in THSA.
Deprotonation in the sulfonate group is very acidic and not detectable in the pH range of determination
(Scheme 2).
pH 7-pH 1 region: The first protonation (pKa = 6.10) of the studied molecule presumably occurs within
this slightly acidic region. The slope of 1.02 for the first protonation of THSA seems to occur at the azo (–
N=N–) group (path I in Scheme 3).31−33 The presence of 3 phenolic hydroxide groups on ring B at the ortho,
meta, and para positions will increase the electron density on βN through mesomeric electron donation. In the
THSA molecule, the electron-donating power of the o-hydroxyl group on ring A has obviously subsided, and
the electron-withdrawing power of the sulfonium group comes into effect, making αN more electron-poor.
pH 1-50% H 2 SO 4 region: The obtained acidity constant for this region was 0.61. The second protonation
of THSA seems to occur on the second azo nitrogen atom, which is next to the quarter nitrogen atom, as depicted
in Scheme 4.
0.1 N NaOH-pH 7 region: The obtained acidity constant for this region was 8.20 (path II in Scheme
5). Therefore, the first deprotonation would be possible from the p-hydroxyl group of ring B (a phenolic
deprotonation).
10 N NaOH-0.1 N NaOH region: The obtained acidity constant for this region was 13.64. The same
situation is acceptable for the second deprotonation (path VII in Scheme 5). The second deprotonation would
be possible from the o-hydroxyl group of ring B (a phenolic deprotonation).
Absorption spectra of aluminum-THSA complex
The UV-Vis spectrum of the aluminum-THSA complex was given against water and ligand (Figure 2). The
aluminum-THSA complex showed maximum absorbance at 480 nm. The reagent showed a minimum absorbance
at the maximum absorbance of the complexes. Therefore, all of the spectral measurements of the complexes
were carried out at 480 nm.
297

¨
Synthesis and spectrophotometric determination of..., T. GURAY, et al.,
Scheme 3. Possible protonation pathways for THSA.
298

¨
Synthesis and spectrophotometric determination of..., T. GURAY, et al.,
OH
HO
OH
OH
HO
OH
A
N
N
H
OH
A
N
H
N
H
OH
B
B
HO3S
HO3S
H
O
H
H
Scheme 4. Possible second protonation for THSA.
Effect of pH
It is well known that the acidity of the medium has an important effect on complexation. The variation of the
absorbance of the aluminum-THSA complex was investigated in a wide pH range. The obtained results are
given in Figure 3. These show that the aluminum-THSA complex had a maximum absorbance at pH 5. For
this reason, the UV-Vis spectrum of the aluminum-THSA complex was given at pH 5 against water and ligand
(Figure 2).
0.6
0.5
0.4
0.3
0.2
0.1
0
1.5
1
2
1
0.5
0
3
480
300
350
400
450
500
550
600
0
2
4
6
8
10
12
Wavelength, nm
pH
Figure 2. The UV-Vis spectra of 1) the THSA (blank
water), 2) the complex (blank water), and 3) the complex
(blank ligand); CM = 2 × 10−5 mol L−1 , CL = 8 ×
10−5 mol L−1 , pH = 5.
Figure 3. The variation of the absorbance of the
aluminum-THSA complex versus pH at 480 nm, CM
2 × 10−5 mol L−1 , CL = 8 × 10−5 mol L−1 , blank
reagent.
=
Calibration curve
Under the optimum conditions given in “General Procedure for Determination of Aluminum,” the complex
absorbance obeys Beer’s law in the aluminum ion concentration range of 0.018-1.075 μg mL−1 . The molar
absorption coefficient was found to be 4.17 × 104 L mol−1 cm−1
absorbance and concentration was found to be as follows:
. The linear relationship between the
(A = 0.0312C + 0.0542, r = 0.9988).
299

¨
Synthesis and spectrophotometric determination of..., T. GURAY, et al.,
Scheme 5. Possible deprotonation pathways for THSA.
300

¨
Synthesis and spectrophotometric determination of..., T. GURAY, et al.,
50% H2SO4
super acidity region
pH=7
10 N NaOH
pH=1
0.1 N NaOH
super basicity region
basicity region
acidity region
Scheme 6. Used acidity scale for acidity of THSA.
Here, C is μg Al(III) 25 mL−1 and A is the absorbance of the complex solution.
Effect of the ligand concentration
In the case of the addition of the increased concentrations of THSA to aluminum solution, the absorbance of
the aluminum-THSA complex increased and became constant in 8 × 10−5 mol L−1 THSA at 480 nm. For
this reason, the present study was carried out with the 8 × 10−5 mol L−1 THSA concentration.
Effect of temperature and standing time
The aluminum immediately formed the complex with THSA, and the absorbance of this complex remained
constant for 3 days. The complex was stable at up to 60 ◦ C.
Effect of interfering species
The effect of the interfering species upon the complex was investigated by the use of the proposed method at
optimum conditions. Fe(III) and Cu(II) interferences were masked by using ascorbic acid and thiourea masking
agents, respectively. The results are given in Table 3.
Composition of the complex
The molar composition of the complex was studied using Job’s method and the mole ratio method, which
indicated a 1:1 ratio of aluminum and THSA in the complex.
Applications of the method
Determination of aluminum in artificial mixture
Some different artificial mixtures were prepared, and these mixtures were analyzed by this method. The method
was successfully applied to aluminum determination in an artificial mixture. The mixtures were prepared as
follows:
I- 0.5 mg aluminum + 5 mg Fe3+ + 1 mg Zn2+
II- 0.5 mg aluminum + 5 mg Fe3+ + 1 mg Co2+
These mixtures were transferred into 50-mL calibrated flasks and diluted with a buffer solution of pH
5. Aliquot parts of these solutions, in the range of 0.2-0.8 μg mL−1 , were put into a 25-mL calibrated flask.
The absorbances at 480 nm were recorded according to the general procedure. It was observed that samples
containing 0.2-0.8 μg mL−1 of aluminum ion could be analyzed with a standard deviation (s) ≤ 0.045 (I) and
301

¨
Synthesis and spectrophotometric determination of..., T. GURAY, et al.,
0.039 (II) for the ion. In order to ensure the accuracy of the method, 5 replicated measurements were carried
out with standard solutions containing 0.5 μg mL−1 (I and II) of aluminum. The accuracy was calculated from
the equation of absolute value of accuracy (%):
|(Found Al – (Spiked Al + Aliquot Al)) × (Spiked Al + Aliquot Al)−1| × 100.
(6)
The accuracy for determination was 2.40% (I) and 0.80% (II), respectively.
Table 3. Comparison of the effect of interfering species on the determination of aluminum with THSA at pH 5 and 480
nm. CAl = 2 × 10−5 mol L−1 , CL = 8 × 10−5 mol L−1
.
Interfering
Limiting mass
Interfering
species (I)
F−
Cl−
Br−
I−
MoO24−
AsO−4
Limiting mass
ratio (Al:I)
1:100
species (I)
ratio (Al:I)
1:4000
1:2200
1:4000
1:15
K+
Na+
Mg2+
Pb2+
Bi3+
Hg2+
Cd2+
Mn2+
Cr3+
Sn2+
Sr2+
Be2+
Si2+
Zn2+
1:2500
1:6550
1:7200
1:15
1:25
1:100
1:2300
1:250
1:400
1:150
1:700
1:220
1:55
1:100
B4O27−
HPO24−
SCN−
1:125
1:1540
1:2500
1:2500
1:4000
1:2500
Thiosulfate
Ascorbic acid
Thiourea
1:6
Co2+
1:6
Ni2+
1:6
Fe3+ + Ascorbic acid
Cu2+ + Thiourea
1:13
1:25
Application of the method to alunite
The method was applied to an alunite mineral; 0.1002 g of alunite was put into a platinum crucible with 1 mL of
HClO4 and 3 mL of HF added, and the solution evaporated almost to dryness on the sand bath. After cooling,
1 mL of HClO4 , 1 mL of HNO3 , 2 mL of HCl, and 20 mL of distilled water were added and the solution was
gently warmed until all of the salts dissolved. The solution was cooled and diluted to 100 mL.
From that solution, 1 mL was diluted to 10 mL. The aliquot part of the solution, in the range of 0.018-
1.075 μg mL−1 , was transferred to a 25-mL calibrated flask, and then 2 mL of a 1 × 10−3 M THSA reagent
was added. The obtained mixture was diluted with a buffer solution of pH 5. The absorbance of the colored
solution was measured at 480 nm. The aluminum content of the alunite was 14.276
1.463 (S.D. = 0.355,
302

¨
Synthesis and spectrophotometric determination of..., T. GURAY, et al.,
R.S.D. = 2.487). The obtained result was compared with the XRF value (Al % = 14.358).28 There was good
agreement between the values obtained by the spectrophotometric method and XRF.
Application of the method to pharmaceutical preparations
Aluminum was detected in the same pharmaceutical preparations using the method described in the pharma-
copeia procedures given in USP XXIV.34
r
ꢀ
For the analysis of aluminum, the method was applied to a Mucaine
suspension (containing 100.656
r
ꢀ
mg of aluminum in a 5-mL suspension) and a Kompensan
tablet (54.970 mg of aluminum in a 1-g tablet).
A stock solution of the suspension was prepared by following the pharmacopeia procedure as given in USP
XXIV.34
From the stock solution, 1 mL was taken and diluted to 100 mL. The aliquot part of this solution, in the
range of 0.018-1.075 μg mL−1 , was transferred to a 25-mL calibrated flask, and 2 mL of a 1 × 10−3 M THSA
reagent was added. The obtained mixture was diluted with a buffer solution of pH 5. The absorbance of the
colored solution was measured at 480 nm.
When the proposed method was compared with the pharmacopeia procedure, high reproducibility and
¯
insignificant differences were observed at the 95% probability level (Table 4). The results (X , SD, RSD%, and
confidence limits (CL)) by the proposed method are in good agreement with those of the pharmacopeia procedure
as given in USP XXIV.34 General rules for the quantification of aluminum hydroxide gel were employed for
the acceptance criteria. These allow for the equivalent of not less than 90.0% and not more than 110.0% of the
labeled amount of aluminum hydroxide (Al(OH)3) in aluminum hydroxide gel. Likewise, this rule was employed
for aluminum hydroxychloride and dihydroxyaluminum sodium carbonate.
Table 4. Determination of aluminum in pharmaceutical preparations by the proposed method and the pharmacopeia
procedure.
Proposed method (n = 8)
Pharmacopeia procedurea (n = 8)
Mucaine
suspensionb
99.811
Kompensan
tabletc
53.917
98.084
2.312
Mucaine
suspensionb
101.912
101.250
2.030
Kompensan
tabletc
¯
X(mg)
55.789
¯
X (%)
99.152
101.490
3.355
dS.D. (s)
1.090
eR.S.D. (%)
1.092
4.288
1.99
6.014
f CL (P = 0.05) 99.811 0.911
53.917 2.870 101.912 1.700 55.789 4.166
r
ꢀ
r
a Ref. 34, b Mucaine
tablet−1 d S.D. (s) =
suspension: 100.66 mg Al 5 mL suspension−1
,
c Kompensan
tablet: 54.970 mg Al 1 g
ꢀ
2
2
2
(x −x) +(x −x) +.....+(x
i1 i2
−x)
s
f
ts
e R.S.D. (%) = X¯ .100, CL =X
iN
¯
√
,
,
N−1
N
Conclusion
In this study, a novel azo dye, THSA, was synthesized, and we proved the feasibility of a UV-Vis spectroscopic
method that uses absorbance values to determine the ionization constants of THSA in water solutions.
303

¨
Synthesis and spectrophotometric determination of..., T. GURAY, et al.,
The new UV-Vis spectrophotometric method was developed for determination of aluminum. Earth
alkaline, alkaline elements, rare earth elements, halides, phosphates, Mn2+ , Hg2+ , Sn2+ , Cr3+ , Cd2+ , and
Sr2+ did not interfere in this method. Molar absorptivity of the complex was 4.17 × 104 L mol−1 cm−1 . The
stoichiometry of the complex was found to be 1:1 at optimum conditions. The method obeyed Beer’s law in the
range of 0.018-1.075 μg mL−1
.
This new reagent does not require surfactants for enhancement of the selectivity and sensitivity of the
method and does not require separation techniques like extraction.
This method has been successfully applied to alunite mineral and certified pharmaceutical preparations.
In conclusion, the developed method is selective, sensitive, reproducible, rapid, simple, and economical. Hence,
this method can be successfully applied as an alternative to existing methods for determination of aluminum.
Acknowledgements
We are grateful to the Research Fund of Eski¸sehir Osmangazi University for the financial support for this work
with Project No. 200319011.
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