Anal. Methods Environ. Chem. J. 6 (4) (2023) 19-36
Research Article, Issue 4
Analytical Methods in Environmental Chemi s try Journal
Journal home page:
Rapid extraction and separation of mercury in water and food
samples based on micelles and azo-thiazoles complexation
before determination by UV-Vis Spectrophotometry
Hesham H. El-Fekya,*, Talaat Y. Mohammeda, Alaa S. Amina and Mohammed A. Kassema, b
a Chemis try Department, Faculty of Science, Benha University, Benha 13518, Egypt.
b Chemis try Department, Faculty of Applied Science, Umm Al-Qura University, Makkah, Saudi Arabia
A simple and sensitive procedure has been es tablished for analyzing
mercury (II) ions spectrophotometrically in the presence of micellar
medium using three azo-thiazoles complexing reagents: 2-amino-
6-(thiazole-2-yldiazenyl)-3-pyridinol (C8H7N5OS), 8-hydroxy-7-
(thiazole-2-yldiazenyl) quinoline-5-sulfonic acid (C12H8N4O4S2), and
1-hydroxy-4-(thiazole-2-yldiazenyl)-2-naphthoic acid (C14H9N3O3S).
H1 NMR spectra validated the three azo thiazoles synthesized
material. Tween 80 (polysorbate 80) and cetyltrimethylammonium
bromide (C19H42BrN as molecular biology) are micellar mediums
to enhance sensitivity. Absorbances were measured for Hg (II)
complexation with R1, R2, and R3 at λmax of 617, 633, and 554 nm,
respectively. The UV-Vis spectrophotometer showed calibration
curves in the 0.2-15 mg L-1. The molar absorptivity, Sandell’s
sensitivity, detection, and quantication limits (LOD, LOQ) were
determined. The interferences of various ions were inves tigated, and
a s tatis tical assessment of the results was performed. The methods
have been applied for trace determination of mercury (II) in food
and environmental water samples. For food samples, all samples
were diges ted before complexation with the azo-thiazoles material
at optimized pH before determination by UV-Vis spectrophotometry.
UV-Vis spectrophotometry,
Water and Food samples
Received 15 Aug 2023
Revised form 13 Oct 2023
Accepted 11 Nov 2023
Available online 29 Dec 2023
*Corresponding Author: Hesham H. El-Feky
1. Introduction
Environmental monitoring is a subject that requires
the development of novel analytical methods. The
speciation of potentially hazardous metal ions is
essential for comprehending their eco-toxicological
and biological properties, which depend on the
chemical species. Extensive research has been
devoted to developing sensitive, relatively simple,
accurate, rapid, and cos t-eective methods for
determining indus trially pertinent metals that may
harm human health [1]. Mercury is a problematic
natural pollutant because it can hurt almos t all living
things [2]. As a result of human environmental
achievements, mercury compounds can exis t in
various settings [3]. They frequently exis t in trace
amounts in natural water types [4]. Mercury
pollution is a signicant problem in the lakes
and rivers near indus trial zones. Therefore, it is
essential to develop new, selective, ecient, and
cos t-eective monitoring procedures for mercury
ions [5]. Low Hg (II) concentrations in the target
species pose a signicant challenge in mercury
determination. In naturally occurring water samples,
the predominant forms of mercury are inorganic
mercury (mercurous and mercuric) and organic
mercury (CH3Hg+). Modern records indicate that
the total (Hg2+, MHg+) concentrations range from
0.2-100 ng L-1 and the organic mercury (CH3Hg+)
has a a concentration of 0.05 ng L-1 in water [6].
Many analytical techniques, such as inductively
coupled plasma (ICP) [7], cold vapour atomic
absorption spectrometry (CV-AAS) [8], neutron
activation analysis (NAA) [9], x-ray uorescence
[10], atomic uorescence spectrometry (AFS) [11],
and spectrophotometric technique [12] had been
advanced to monitor mercury ion at a micro level.
Each of the above methods has some advantages;
however, they may have disadvantages, such as
low reproducibility and limited sample exibility.
Without pre-concentration, the inductively coupled
plasma method was suitable for determining trace
amounts of Hg (II). However, this ins trument
is quite expensive to purchase and maintain.
Additionally, this technique has some signicant
interference [11]. Due to its simplicity, atomic
absorption spectrometry was a suitable and widely
utilised technique for accurate Hg(II) determination.
In the meantime, its application is limited due to
its limited linear range and signicant spectral
interference from volatile subs tances [13]. Due to
the low Hg (II) concentration, these practises are not
directly applicable to environmental and biological
models and/or frequently require pre-concentration
s teps to enhance selectivity. Several photometric
reagents have been used for spectrophotometric
mercury ion determination. Dithizone was the mos t
common reagent used for this purpose [14]. Before
photometric analysis, the Hg(II)-dithizone complex
is taken out with either CCl4 or CHCl3 [15]. Based
on the absorbance measurements of the formed
complexes in the presence of surfactants, we report
for the rs t time the direct spectrophotometric
determination of the Hg(II) ion with three novel azo
dyes. Also, many methods based on nanotechnology
were used for mercury extraction/removal from
dierent water, air, human and food (vegetable and
nut) samples. Mousavi et al used Tetraethyl thiuram
disulde [(C2H5)2-NCSS2CSN-(C2H5)2; TET] mixed
with ionic liquids for extraction/speciation mercury
in human samples by dispersive liquid-liquid
microextraction (DLLME) coupled to CV-AAS
[16]. Osanloo et al used silver nanoparticles coating
on micro glassy balls for removal mercury from air
and Rouhollahi et al can be determined mercury
in air and human samples [17-19]. Golbabaei,
Bagheri and hassani showed that mercury can be
determined in biological human samples based on
adsorbent by the CV-AAS. In addition, they used
the nano-palladium functionalized on the silica
nanoparticles for mercury removal from air by the
GFSC method [20-22]. Moreover, some methods
based on adsorbents such as MWCNTs, pyrrolic
and pyridinic nitrogen doped porous graphene
nanos tructure(N-D-PNG) extracted mercury from
water, food, and air samples [23-25].
In this s tudy, we prepared the azo dyes based
on new synthesis include, 2-amino-6-(thiazole-
2-yldiazenyl)-3-pyridinol (C8H7N5OS) [R1],
8-hydroxy-7-(thiazole-2-yldiazenyl) quinoline-5-
sulfonic acid (C12H8N4O4S2) [R2], and 1-hydroxy-
4-(thiazole-2-yldiazenyl)-2-naphthoic acid
(C14H9N3O3S) [R3] (Fig. 1). The H1 NMR spectra
of all synthesized azo dyes. Herein, Hg(II)
was successfully measured at the micro level
in dierent water and food samples using the
proposed methodologies by UV-Vis spectrometry
after complexation with azo dyes. The food
samples were diges ted before the complexation
and determination procedure. The approach has
several advantages, including its low cos t, ability to
be applied to real samples, and broad linear range.
2. Experimental
2.1. Ins trumentation
All absorption measurements are taken with a
Jasco UV-Vis spectrophotometer (model V530,
Jasco, Tokyo, Japan) with a scanning speed of
400 nm/min, a bandwidth of 2.0 nm, and 1.0 cm
pair-matched quartz cells. A pH meter (HI 8014,
HANNA Ins truments, Woonsocket, RI, USA) was
used to adjus t the pH of all solutions. We used a
Fluoromax-4 (Horbiba Scientic, Kyoto, Japan)
for the spectrouorimetric observations. Both the
excitation and emission slit widths were 9 nm.
Anal. Methods Environ. Chem. J. 6 (4) (2023) 19-36
2.2. Reagents and Chemicals
All chemicals and reagents employed in this s tudy
were of analytical grade (Merck, Darms tadt,
Germany), and the solutions were prepared using
bi-dis tilled water. A s tock solution of 1×10-2 M
mercuric chloride was prepared by weighing out
0.679 g HgCl2.2H2O, dissolved in the leas t amount
of bi-dis tilled water and completed in a 100-mL
measuring ask to the mark with bi-dis tilled water.
The s tock solution was then s tandardized by EDTA
[26]. All used solutions were carefully diluted from
a s tock solution. At room temperature, the solution
held up for a whole month. The preceding method
was used to prepare universal buer solutions. As
a result of the low Hg (II) concentration, these
methods are either not directly applicable to
environmental and biological models or necessitate
additional pre-concentration processes to increase
selectivity. Mercury ion concentrations have been
measured spectrophotometrically using a variety
of photometric reagents. The mos t commonly
used reagent for this was dithizone [27]. Tween
80 [0.5% (v/v)], Triton X-100 [0.5% (v/v)],
cetyltrimethylammonium bromide (CTAB) [0.5%
(w/v)], and sodium dodecyl sulphate (SDS)
[0.5% (w/v)] were used as surfactants due to their
commercial availability in a highly puried form,
low toxicity, and low charge. Tween 80 and Triton
X-100 were prepared by adding 0.5 mL of each
surfactant to 50 mL of bi-dis tilled water and then
bringing the volume to 100 mL to achieve a 0.5%
(v/v) solution. In the case of SDS and CTAB, a
0.5% (w/v) solution was intended by dissolving 0.5
g of the surfactant in 50 mL of bi-dis tilled water
and then lling a 100 mL measuring ask with bi-
dis tilled water to the desired volume. Nitric acid
(HNO3), 70 %, and hydrogen peroxide (H2O2),
30 % (w/w) in H2O, were obtained from Aldrich.
Rapid mercury determination by azo-thiazoles and UV-Vis Hesham H. El-Feky et al
Fig.1. Synthesis of azo dyes include, 2-amino-6-(thiazole-2-yldiazenyl)-3-pyridinol (C8H7N5OS)
[R1], 8-hydroxy-7-(thiazole-2-yldiazenyl) quinoline-5-sulfonic acid (C12H8N4O4S2) [R2],
and 1-hydroxy-4-(thiazole-2-yldiazenyl)-2-naphthoic acid (C14H9N3O3S) [R3]
2.3. Synthesis of reagents
A solution of 2-aminothiazole (10.014 g, 0.1 mole)
dissolved in 1:1 (v/v) HCl aqueous solution was
cooled in an ice bath at ca. – 5.0 oC. To this solution,
while s tirring vigorously, a cold aqueous solution of
sodium nitrite (6.903 g, 0.1 mole) was added, and
the reaction mixture was kept in an ice bath at a
temperature range of 0-5.0oC for 30 min. The obtained
cold diazonium salt was used for coupling with an
equivalent quantity of cold solution of 2-amino-3-
hydroxypyridine (11.01 g, 0.1 mole), dissolved in
10 % (w/v) NaOH. The formed azo dye (R1) was
kept for 40 min in an ice bath at ca. -5.0oC, ltered
o, washed with bi-dis tilled water, and dried. The
obtained azo compound was nally re-crys tallized
using absolute C2H5OH. For the preparation of the
other azo compounds, 8-hydroxy-7-(thiazole-2-
glaze) quinoline-5-sulfonic acid [R2] and 1-hydroxy-
4-(thiazole-2-ylazo)-2-naphthoic acid [R3], a typical
procedure was used using 8-hydroxyquinoline-5-
sulphonic acid (26.125 g, 0.1 moles) and 1-hydroxy-
2-naphthoic acid (18.81 g, 0.1 moles), respectively.
The reaction yield was in the range of 75-85 %.
The azo compounds showed a sharp melting
point, indicating high purity. The compounds were
characterized using 1H-NMR spectroscopy (Fig. 2a-
c). The reagent solutions were prepared by dissolving
0.110, 0.033 and 0.148 g of R1, R2 and R3 in 100 mL
ethanol to obtain 5×10-3, 1×10-3 and 5×10-3 mol L-1 of
R1, R2 and R3, respectively.
2.4. General procedure
In a typical procedure, for the reagents R1 and R2,
an appropriate volume of the sample containing 1 ×
10-3 M of Hg(II) was placed in a 10 mL measuring
ask. The universal buer of pH 6.0 (5 mL) or pH
Anal. Methods Environ. Chem. J. 6 (4) (2023) 19-36
Fig. 2a. 1H-NMR spectroscopy of 2-amino-6-(thiazole-2-yldiazenyl)-3-pyridinol (C8H7N5OS) [R1]
Fig. 2b. 1H-NMR spectroscopy of 8-hydroxy-7-(thiazole-2-yldiazenyl) quinoline-5-sulfonic acid (C12H8N4O4S2) [R2]
R1 R2 R3