Comparative evaluation of trace heavy metal ions in water sample using complexes of dithioligands by flame atomic absorption spectrometry

Article abstract of DOI:10.13005/ojc/340111

Four new complexes were prepared by the metathetic reaction of trace heavy metals like Cd, Zn, Cu and Hg with two different dithioligands of the formula ML₂ [M= Cd, Zn, Cu and Hg and L= potassium-1,1-dicyano-2,2-ethylenedithiolate and potassium

Full text of DOI:10.13005/ojc/340111

ISSN: 0970-020 X
CODEN: OJCHEG
018, Vol. 34, No.(1):
Pg. 100-109
ORIENTAL JOURNAL OF CHEMISTRY
An International Open Free Access, Peer Reviewed Research Journal
2
www.orientjchem.org
Comparative Evaluation of Trace Heavy Metal Ions in
Water Sample Using Complexes of Dithioligands by
Flame Atomic Absorption Spectrometry
VINAY KUMAR MAURYA, RAVI PRATAP SINGH and LAL BAHADUR PRASAD*
Department of Chemistry, Institute of Science, Banaras Hindu University, Varanasi- 221005, India.
*
Corresponding author E-mail: lbprasad@bhu.ac.in
http://dx.doi.org/10.13005/ojc/340111
(Received: November 03, 2017; Accepted: December 15, 2017)
ABSTRACT
Four new complexes were prepared by the metathetic reaction of trace heavy metals like
Cd, Zn, Cu and Hg with two different dithioligands of the formula ML [ M= Cd, Zn, Cu and Hg and
2
L= potassium-1,1-dicyano-2,2-ethylenedithiolate and potassium N-4-fluorobenzyl,
1
13
N butyldithiocarbamate ] and characterized by elemental analysis, IR, UV-visible, H, C NMR and
AAS. Atomic Absorption Spectrophotometric measurements revealed that the N- substituted
dithiocarbamate ligand are more effective. Removal efficiency of heavy metals than carbon
substituted dithiocarbamate ligand. Molar ratio studies show that the complexes have the formula
ML . Solvent extraction measurement indicates that after the extraction of heavy metal in water
2
phase and their dithiocarbamate complexes are completely dissolved in organic phase and are
totally separated from aqueous solution.
Keywords: Atomic Absorption Spectrometry, Dithiocarbamate, Heavy Metal, Removal
Efficiency, Polluted Water.
INTRODUCTION
agrochemicals due to their high efficiency for fungal
7
-10
diseases
and adopt various coordination modes
Dithiocarbamate functional group is a
versatile ligating moiety and readily interacts with
a verity of metal ions to form complexes with varying
such as asymmetric and symmetric chelating,
bridging and rarely monodentate in their complexes,
the most common binding mode is chelating. The
dithiocarbamate ligands show ability to stabilized
high formal oxidation states of the metals and metal
dithiocomplexes exhibits interesting magnetic and
1
nuclearities . They have wide range of application
in medicinal chemistry, industrial chemistry, rubber
2
-6
technology and several carbon substituted and
N-substituted dithiocarbamate complexes used in
1
1-12
optical properties
.
This is an
.0 International License (https://creativecommons.org/licenses/by-nc-sa/4.0/ ), which permits unrestricted
NonCommercial use, distribution and reproduction in any medium, provided the original work is properly cited.
Open Access article licensed under a Creative Commons Attribution-NonCommercial-ShareAlike
4

PRASAD et al., Orient. J. Chem., Vol. 34(1), 100-109 (2018)
101
Heavy metals are high atomic weight metal- contaminated polluted water depends on
elements and their density about five times greater initial parameters like pH, initial metal concentration
than water. Toxicity of heavy metals depends upon and the overall treatment performance. In this study
the doses of individuals, ways of unveiling and their two different moiety of dithiocarbamate ligands (N-
chemical species, as well as age, gender, genetics substituted & C- substituted) were prepared and
and nutritional states of unveiling individuals. compared their performance for the removal
Environmental water pollution through toxic heavy efficiency of heavy metal from the water sample with
metals has great anxiety and a dangerous problem the help of flame atomic absorption spectrometer.
due to the liberation and prejudicial effects. These
13
metals found through anthropogenic activities and
liberated into the atmosphere, and they destroy the
metabolic function by their accumulation and disturb
MATERIALS AND METHODS
All the experiment were carried out in the
the function of vital organs and glands such as heart, open atmosphere at room temperature. The solvent
14
were dried and distilled before use following the
brain, kidney, bone, liver etc. and or plants . By the
consumption of food, beverages, skin exposure and
the inhaled air these toxins, have been introduced
into our bodies.
standard procedure. The chemicals Malononitrile,
4
-Fluorobenzaldehyde, Butyl amine, NaBH , CS ,
4 2
Dioxane, Dichloromethane, and KOH (E.Merck)
were used as received.
In this article we have chosen pollutants
like cadmium, zinc, copper and mercury. These
metals have wide applications in applied
engineering works, pulp and paper industries,
leather tanning, plastic stabilizers, pigments,
photographic materials, fertilizers, batteries etc.
Additionally, cadmium and lead are known as toxical
effects and have a harmful impact on the humans
Instrumentation
The concentrations of Cd, Zn, Cu and Hg
were determined using a ALICO SL -168 Model
Flame Atomic Absorption Spectrometry (FAAS)
equipped with a hollow cathode lamp. A mixture of
acetylene as a fuel, air as an oxidizing agent and
air acetylene Flame burner were used. The ratio of
the metal to the ligand was determined using a UV-
Spectrophotometer (SHIMADZU 1700). For pH
adjustment, we used a Metrohm pH Meter. The
melting points of the ligands and complexes were
15
health and living organisms . Zinc and copper are
comparatively non-toxic to humans and animals at
low level but toxic to plants and algae at higher
16
level while cadmium replace zinc biochemically ,
causes high blood pressure, kidney damage and
red blood cells and mercury is a highly toxic
particularly as methylmercury, causes irreversible
nerves and brain damage. Many methods have
been adopt for the separation of heavy metals from
recorded by digital melting point apparatus in open
capillary. Infrared spectra were carry out as
KBr Pellets on a Varian Excallibur 3100 FT-IR
-
1
Spectrophotometer in the range of 4000-400 cm .
The contents of C, H, N, were determined with the
various water sample before being discharged into help of an Elementar Analysen System GmbhVario
the atmosphere but in some cases difficulties are EL V 3.00 instruments.
arises in determining the heavy metals in the
Preparation of ligands
Preparation of potassium-1,1-dicyano-2,2-
ethylenedithiolate (KL1)
environmental samples due to scanty sensitivity and
1
7-18
or matrix interferences
.
Therefore, a new approach of separation
The ligand KL was synthesized by the
1
21
and enrichment for heavy metals ions and reported method with some minor modification . To
determination by AAS was undertaken here. It is a suspension of pulverized KOH(11.2 g, 0.2 mol) in
used as usual instrumental techniques for the dioxane, a mixture of carbon disulphide (6.3 ml, 0.1
analysis of element in water samples. It is a very mol) and malononitrile (6.1 ml, 0.1 mol) in the same
1
9-20
sensitive technique and have very low interference
,
solvent (50.00 ml) was added gradually with
and detect element up to few ppm level when constant stirring. The temperature of the reaction
o
graphite furnace is used for the atomization. The mixture was maintained at bellow15 C using an
selection of more appropriate treatment for the ice bath in order to inhibit any possible

1
02
PRASAD et al., Orient. J. Chem., Vol. 34(1), 100-109 (2018)
decomposition of the product due to nature of the
reaction is exothermic. The reaction mixture was
stirred for about 30 min. after the complete addition
of the reactants and after some time it was diluted
with 250 ml of the diethyl ether. The yellowish
precipitate was formed out and it was suction filtered,
washed with mixture of dioxane - ether and dried
in vacuum.
Analysis
Found (calcd.) % for C N S K .H O: C,
4
2
2
2
2
20.28(20.34); N, 11.84(11.86); S, 26.45(27.12); H,
1.06(0.95)
N
N
C
C
N
N
C
C
SK
SK
Dioxane
CH2
2 KOH
CS2
C=C
o
at 15-20 C
Malononitrile
(
Scheme A)
Preparation of potassium N-4-fluorobenzyl,N-
butyldithiocarbamate (KL2)
solvent removal. The dithiocarbamate ligand were
synthesizedby the reaction of the secondary amines
prepared earlier and dissolved in 15 mL THF, KOH
The KL2 ligand was prepared from
secondary amine, obtain by reduction of Schiff
(5.60 g,0.1 mol) and add CS (7.60 g, 0.1 mol) drop
2
2
2-23
base ,which was prepared
by using the
wise with constant stirring under temperature
0
4
-fluorobenzaldehyde (12.4 g, 0.1 mol) and butyl
bellow 10 C . The yellow precipitate was formed
amine (7.30 g, 0.1 mol) and dissolved in 25 mL
ethyl alcohal and refluxed on paraffin oil bath for 8
hours and reducing it by the mixture was kept on
which was again stirring about 4 h and filtered it.
The residue washed with 2-3 times of diethyl ether
and dried .
ice bath, stirred well and then NaBH and methanol
4
were added, the secondary amine produce, then it
was extracted with 50 ml CH Cl solution and
Analysis
Found (Calcd.) % for C H FNS K: C,
2
2
12 15
2
washed with 45 ml distilled water three times . The
oily yellow to light pink product was collected on
48.78(48.84); N, 4.74(4.78); S, 21.70(21.78); H,
5.12(5.18)
C H OH
2
5
o
reflux at 80 c
F
CHOH
F
CH N
H N
2
Butyl amine
p-Flourobenzaldehyde
reduse with
NaBH4
KOH
F
CH2
F
CH2
NH
CS2
ice cold condition
N
C
S
SK
(
Scheme B)

PRASAD et al., Orient. J. Chem., Vol. 34(1), 100-109 (2018)
103
2
2-23
Synthesis of the complexes of heavy metal with molar ratio . All the reaction mixture was stirred
(
KL ) and (KL ) Ligands
for 6 h at room temperature for the precipitation of
metal-complexes. The precipitate obtain was
1
2
The complexes were prepared by taking filtered and washed with methanol followed by
0 mL methanolic solution of the ligands KL1 (0.218 diethyl ether and analyzed by different
2
g, 1 mmol) and KL (0.295 g, 1 mmol) and 20 mL spectroscopic techniques. The elemental analysis
2
methanol: water (80:20) solution of M (OOCCH ) . data and % yield of the prepared complexes are
3
2
2
H O ( 0.5 mmol) [M= Cd, Zn, Cu and Hg] in 2 : 1 shown in Table 1 and 2.
2
Table. 1:The elemental analysis (%) and the yield (%) of complex formation for ligand KL1
S.No.
Complexes
C %
N %
S %
Metal %
Yield (%)
1
2
3
4
[Cd(C N S ) ]
28.58(28.34)
27.94(27.12)
27.79(27.47)
24.75(24.23)
16.66(15.96)
16.29(16.02)
16.20(15.98)
14.43(14.03)
38.15(37.12)
37.29(37.16)
37.09(36.86)
33.04(32.82)
16.61(15.89)
18.48(18.32)
18.91(18.48)
27.78(27.32)
98.72
99.01
99.18
98.79
4
2
2 2
[Zn(C N S ) ]
4
2
2 2
[Cu(C N S ) ]
4
2
2 2
[Hg(C N S ) ]
4
2
2 2
Table. 2:The elemental analysis (%) and the yield (%) of complex formation for ligand KL2
S.No.
Complexes
C %
H %
N %
S %
Metal % Yield (%)
1
2
3
4
[Cd(C H NFS ) ] 50.69(50.46) 5.32(5.11) 4.93(4.86) 22.56(22.12) 9.82(9.78) 98.88
1
2
15
2 2
[Zn(C H NFS ) ] 50.02(49.89) 5.25(5.13) 4.86(4.78) 22.26(22.16) 11.03(10.92) 99.09
12
15
2 2
[Cu(C H NFS ) ] 49.86(49.78) 5.23(5.16) 4.85(4.73) 22.18(22.07) 11.31(11.24) 99.21
1
2
15
2 2
[Hg(C H NFS ) ] 46.45(46.13) 4.87(4.39) 4.51(4.42) 20.67(20.51) 17.38(17.22) 98.93
1
2
15
2 2
-
1
-1
RESULTS AND DISCUSSION
observed in 2190-2207 cm and 1383-1395 cm
region in all the complexes.
Infrared spectra
The ligands (KL1 and KL ) act as a
The splitting in ϑ(C≡N) observes in the
bidentate ligand. The (KL ) ligand can be most of the complexes may be related to the lower
2
1
represented in three forms as shown under
symmetry for these complexes. This may be
indicative of bidentate bridging behavior of (KL )
1
-1
The ligand (KL ) and all the complexes ligand. The ϑ(C-S) vibration occurring at 950 cm and
1
-
1
-1
-1
-1
shows IR absorption near 2000 cm , 1400 cm and 874 cm in (KL ) is observed in 866-950 cm region
50 cm associated to ϑ(C≡N), ϑ(C=C) and ϑ(C-S) in the complexes thereby indicating coordinating
. The two most important behavior of isomaleonitriledithiolate ligand.
feature of the spectra are the shift 12-30 cm in
ϑ(C≡N) and 15-21 cm in ϑ(C=C) from the ligand
KL ) spectra to that of the complexes. In ligand showed the IR absorption near 2926 cm ,1206
spectra, two bands ϑ(C≡N) and ϑ(C=C) are located cm ,1149 cm and 994 cm associated to ϑ(CH3),
near at 2178 cm (split band) and 1375 cm
1
-
1
9
2
6-27
mode respectively
-
1
-
1
The ligand (KL ) and all the complexes
2
-
1
(
1
-
1
-1
-1
-
1
-1
ϑ(C-N), ϑ(C=S) and ϑ(C-S) mode respectively.Upon
-
1
respectively. Upon complexation these bands are complexation these bands are shifted 14-19 cm in
N
N
C
C
N
C
C
N
N
C
S
S
S
S
C=C
C
C
C
C
N
S
C
S
(
I )
(
II )
( III )

1
04
PRASAD et al., Orient. J. Chem., Vol. 34(1), 100-109 (2018)
-
1
-1
ϑ(C=S), 6-12 cm in ϑ(C-S) and 11-18 cm in
we take zinc metal and their concentration fixed at
5 pp min. a solution at pH 7 considered as blank
sample. Then the absorbance of the sample to be
determines containing the metal plus the ligand at
concentration i.e. 1, 2, 4, 6, 8, 10, 12, 15, 20 and 25
ppm respectively. By the extrapolating the graph,
the intercept of plot becomes 10 ppm, this is the
double concentration of the metal, suggesting that
23
ϑ(C-N) in all the complexes .
Yoe-Jones Method for the Determination of
Stoichiometry of complexes
In this studies, a set of series of sample
solution were prepared in which the concentration
of one reactant is kept as constant and other is
different. The absorbance of each solution is
determined and plot a graph between absorbance
and the concentration of the ligand. For example
2
4-25
a complex have formula ML2 . This method was
repeated for each metals with both ligands. A
representative example are shown in Figure. 1 and 2.
Fig. 1. Determination the of Zn ratio to (KL ) ligand
1
Fig. 2. Determination of Zn ratio to (KL ) ligand
2

PRASAD et al., Orient. J. Chem., Vol. 34(1), 100-109 (2018)
105
The Solvent extraction of the heavy metal 9-11.Our main aim for the extraction of heavy metal
dithiocarbamate
from water solution is to separate trace level of heavy
metal ions from the solution. The heavy metal
precipitateted as metal dithiocarbamate complex
0
.1% of known amount of ligands was
taken in R.B. and 0.05 mg/L and 5 mg/L water
standered solution of heavy metal ions was added
and stirred for 30 min. at room temperature. Similarly
the metal complexes were extracted with 10 ml
of dichloromethane solution. The heavy metal
absorbance in water phase was determined by
atomic absorption spectrometry (flame system and
furnace system) at different pH (3-11) after removing
the organic phase of the solution and it was
compared with the absorbance of initial solution of
heavy metal ion (0.05 and 5.0 mg/L HM standard
solution). The pH of the solution was adjusted with
HCl and NaOH or maintained by a suitable buffer
at desired volume. Acetate buffer for pH 3-5,
after using 10 ml volume of the CH Cl solution for
2
2
the extraction. The absorbance of heavy metal
ions (0.050 and 5.0 mg/L) are measured before
and after adding the dithiocarbamate solutions by
the atomic absorption spectrometry. After the CH Cl
2
2
extraction shows that absorbance of trace heavy
metal ions in the water phase is lower than the
absorbance of initial concentration of trace heavy
metal solution by the AAS measurement. This
measurement demonstrate that after the extraction
of heavy metal in water phase and their
dithiocarbamate complexes are completely
dissolved in organic phase and are totally separated
phosphate buffer of 6-8 and carbonate buffer for pH from water solution.
Table. 3: Metal removal efficiency of KL1 ligand with 0.05 mg metals
Metal
Cd
Initial concentration
ppm)
Remaining concentration in
aqueous solution (ppm)
pH
Removal
(
efficiency (%)
0.813
0.941
0.792
0.911
0.172
3
5
78.84
79.33
87.20
84.87
83.27
0
0
0
0
.168
.104
.123
.136
7
9
11
Zn
Cu
Hg
0.197
3
5
79.06
82.78
84.27
89.58
86.29
0
0
0
0
.162
.148
.098
.129
7
9
11
0.115
3
5
85.47
86.48
89.52
90.40
87.37
0
0
0
.107
.083
.076
7
9
0
.1
11
0.172
3
5
81.11
83.42
88.03
89.24
84.96
0
0
0
0
.151
.109
.098
.137
7
9
11

1
06
PRASAD et al., Orient. J. Chem., Vol. 34(1), 100-109 (2018)
Table. 4: Metal removal efficiency of KL ligand with 5 mg metals
1
Metal
Cd
Initial concentration
ppm)
Remaining concentration in
aqueous solution (ppm)
pH Removal
efficiency (%)
(
0.911
0.137
3
5
84.96
85.83
86.60
85.62
84.74
82.25
82.82
83.61
86.12
85.21
87.09
88.41
89.02
89.74
88.05
86.03
86.46
86.24
87.95
85.60
0
0
0
0
.129
.122
.131
.139
7
9
11
3
5
Zn
0.879
0.829
0.156
0
0
0
0
.151
.144
.122
.130
7
9
11
3
5
Cu
0.107
0
0
0
0
.096
.091
.085
.099
7
9
11
3
5
Hg
0.938
0.131
0
0
0
0
.127
.113
.129
.135
7
9
11
Table. 5: Metal removal efficiency of KL ligand with 0.05 mg metals
2
Metal
Cd
Initial concentration
ppm)
Remaining concentration in
aqueous solution (ppm)
pH Removal
efficiency (%)
(
0.921
0.087
3
5
90.55
91.20
92.50
92.07
90.77
87.08
87.84
88.27
91.04
89.59
91.93
92.61
93.75
94.43
93.18
91.91
92.50
92.98
94.05
93.22
0
0
0
0
.081
.069
.073
.085
7
9
11
3
5
Zn
0.759
0.880
0.098
0
0
0
0
.095
.089
.068
.079
7
9
11
3
5
Cu
0.071
0
0
0
0
.065
.055
.049
.060
7
9
11
3
5
Hg
0.841
0.068
0
0
0
0
.063
.059
.050
.057
7
9
11

PRASAD et al., Orient. J. Chem., Vol. 34(1), 100-109 (2018)
107
Table. 6: Metal removal efficiency of KL ligand with 5 mg metals
2
Metal
Cd
Initial concentration
ppm)
Remaining concentration in
aqueous solution (ppm)
pH
Removal
efficiency(%)
(
0.965
0.099
3
5
7
9
11
3
5
7
9
11
3
5
7
9
11
3
5
7
9
11
89.74
91.08
91.60
90.77
89.94
87.72
88.19
88.31
89.96
88.42
89.90
90.62
91.24
92.58
91.65
90.41
91.07
92.40
92.84
91.85
0
0
0
0
.086
.081
.089
.097
Zn
0.847
0.971
0.104
0
0
0
0
.100
.099
.085
.098
Cu
0.098
0
0
0
0
.091
.085
.072
.081
Hg
0.908
0.087
0
0
0
0
.081
.069
.065
.074
Fig. 3. Effect of pH on the % recovery of heavy
Fig. 4. Effect of pH on the % recovery of heavy
metal ions (0.05 mg) with KL ligand
1
metal ions (5 mg) with KL ligand
1
Fig. 5. Effect of pH on the % recovery of heavy
Fig. 6. Effect of pH on the % recovery of heavy
metal ions (0.05 mg) with KL ligand
metal ions (5 mg) with KL ligand
2
2

1
08
PRASAD et al., Orient. J. Chem., Vol. 34(1), 100-109 (2018)
Metal removal capacity of ligands
The method involved for trapping metals
dithiocarbamate metal complexes shows higher
stability than the C-substituted dithiolate metal
complexes due to presence of free lone pair on the
nitrogen which upon delocalization the partial
C−N double bond character after the complexation,
indicating the removal efficiency primarily depends
on the types of ligands are used.
from its solution using different dithiocarbamate
ligands (KL and KL ) were study using AAS at
1
2
different pH values. The result obtained by AAS
measurement shown in table 3-6 indicate that
removal efficiency of all the heavy metals are varies
with varying the pH. The optimal removal efficiency
was found 87.20 % in the case of cadmium metal
CONCLUSION
(
0.05 mg) with ligand KL at pH 7; but when water
1
All the complexes were found in 98.72-
sample were spiking with 5 mg of metal with same
ligand, the removal efficiency are decrease i.e.
9
9.21% of yields by facile metathetical reactions
between metals and the potassium salt of the ligands
KL and KL ) in a 1:2 molar ratio in 80:20 v/v methanol:
8
6.60 % this is because when the concentration of
(
1
2
metal reaches at 100 times the stability of ligand-
metal complex are decrease. Whereas in basic and
water solution. The complexes are stable at r.t. and
o
melt/decomposeinthe135-200 Ctemperature range.
acidic medium lower efficiency of KL ligand with
1
All the ligands and complexes have been analyzed
cadmium metal was observed. Likewise the
removal efficiency was observed at maximum 89.58
%
1
by different spectroscopy techniques like IR, H and
13
C NMR and UV-Vis Spectroscopy.The ultraviolet
at highly basic medium for zinc metal and it was
0.40 % and 89.24 % observed for copper and
spectroscopy clearly indicate that the complexes
9
have the formula ML .The dichloromethane
2
mercury at basic medium. Whereas the highest
removal efficiency 92.50 % was noted in the case
of cadmium metal at pH 7 with 0.05 mg of metal
extraction of the heavy metal complexes showed
that it was quantitatively pass from the water phase to
the small volume of the organic phase and were
successfully separated into organic phase. It was
observed that the N-substituted dithiocarbamate ligand
was more effective in removing the trace heavy metal
ions from water sample solution compared to the
C-substituted dithiocarbamate ligand at the same
pH value.
with ligand KL while when the water sample spike
2
with 5 mg of the metal the efficiency decrease 91.60
%
, this indicate that when the water sample is
contaminated maximum with cadmium metal the
removal efficiency decrease. Same observation
was observed for another heavy metal ions. So, pH
values and concentration of metal plays an
important role in the removing efficiency for the
heavy metal ions and it was changes upon
changing the pH and metal concentration for the
same ligand. The graphical representation of pH
vs % removal efficiency was shown in Figure. 3-6.
ACKNOWLEDGEMENT
We gratefully acknowledge the University
Grant Commission (UGC), New Delhi for financial
assistance in the form of Senior Research Fellow
Ref. No: 22/12/2013 (II) EU-V. Authors are thankful
to Mr. Himanshu, Department of Metallurgical
Engineering, IIT, B.H.U. Varanasi for the FAAS
measurement.
Finally, it was observed that the ligand KL2
have higher removal efficiency in comparison to
the ligand KL , this is because the N-substituted
1
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