A dual colorimetric chemosensor based on Schiff base for highly selective and simultaneous recognition of CN? and Sn2+

Article abstract of DOI:10.1016/j.ica.2019.119372

A new colorimetric chemosensor 2-methoxy-6-{(E)-[(4-methylphenyl)imino] methyl}-4-[(E)-(4-nitrophenyl)diazenyl] phenol (SZ) was designed and synthesized for simultaneous detection of CN^? and Sn²⁺ in MeCN: bis-tris buffer solution. Th

Full text of DOI:10.1016/j.ica.2019.119372

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Research paper
A dual colorimetric chemosensor based on Schiff base for highly selective and
simultaneous recognition of CN − and Sn2+
Pravin R. Dongare, Anil H. Gore, Balu D. Ajalkar
PII:
S0020-1693(19)31727-X
https://doi.org/10.1016/j.ica.2019.119372
ICA 119372
DOI:
Reference:
Inorganica Chimica Acta
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3 November 2019
14 December 2019
14 December 2019
Please cite this article as: P.R. Dongare, A.H. Gore, B.D. Ajalkar, A dual colorimetric chemosensor based on Schiff
base for highly selective and simultaneous recognition of CN − and Sn2+, Inorganica Chimica Acta (2019), doi:
https://doi.org/10.1016/j.ica.2019.119372
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A dual colorimetric chemosensor based on Schiff base for highly selective
and simultaneous recognition of CN and Sn2+
Pravin R. Dongarea, Anil H. Goreb and Balu D. Ajalkara*
aDepartment of Chemistry, Shivraj College of Arts, Commerce and D. S. Kadam Science
College, Gadhinglaj, Affiliated to Shivaji University, Kolhapur, Maharashtra, 416 502, India
bDepartment of Chemistry, Uka Tarsadia University, Bardoli- Mahuva Road, Tarsadi,
Gujarat, 394 350, India
Abstract:
A new colorimetric chemosensor 2-methoxy-6-{(E)-[(4-methylphenyl)imino] methyl}-4-
[(E)-(4-nitrophenyl)diazenyl] phenol (SZ) was designed and synthesized for simultaneous
detection of CN and Sn2+ in MeCN: bis-tris buffer solution. The sensor SZ showed quick
and selective colorimetric response towards CN and Sn2+ with a change in color from yellow
to pink and colorless respectively without any interfering anions or cations. Meanwhile, the
1
binding mode of SZ for CN and Sn2+ were studied by H-NMR, ESI-MS, FT-IR
spectroscopy, Job’s plot analysis and DFT calculations. The detection limit of SZ towards
CN and Sn2+ was found to be 0.649 µmol/L and 0.754 µmol/L respectively which are lower
than the WHO guidelines for drinking water. Furthermore, chemosensor SZ was successfully
utilized as a colorimetric chemosensor for the detection of CN and Sn2+.
Keywords: Schiff base; Azo dye; Dual colorimetric chemosensor; Cyanide ion; DFT
___________________
*Corresponding Author Email: bajalkar@rediffmail.com

1. Introduction
The design of colorimetric chemosensor for selective sensing of biologically and
chemically important anions and cations has received huge interest in the past decade [1-6].
Among these cyanide gives particular interest for their toxicity to environment and life
system because, cyanide is readily absorbed through alimentary canal, lungs, skin and has
strongest binding affinity to ferric ion present in the enzyme cytochrome-c oxidase, which
inhibit the mitochondrial electron transport chain results loss of consciousness, convulsion,
palpitation and death [7-9]. Nevertheless, cyanide is widely used in industrial processes, such
as textile manufacturing, metallurgy, silver production, herbicides and gold mining which has
led to the inadvertent release of cyanide from industrial waste which is harmful to
environmental and aquatic life [10-13].
Besides, tin is a soft, silvery-white post-transition metal commonly used in
dentifrices, catalysts in the preparation of indole and coumarin derivatives, biodiesel [14-17].
Further, tin is an essential trace mineral for humans and is found in the thyroid gland, liver,
spleen and brain [18, 19]. It also involved in the hair growth and prevention of cancer in
human beings [20, 21]. The deficiency of tin results in decreased hearing loss, shortness of
breath, asthma and diminished hemoglobin synthesis. While, excess accumulation of tin finds
some severe immunotoxic and neurotoxic effects in human cause symptoms generally
gastrointestinal complaints such as nausea, diarrhea, vomiting and cramps [22, 23].Therefore,
it is important to develop chemosensor for the determination of CN and Sn2+ in an aqueous
medium.
In earlier several modern analytical methods for detection of CN and Sn2+ ion has
been developed such as ion-exchange chromatography [24], electrochemical methods [25,
26], flow injection [27] and atomic absorption spectroscopy [28] required sophisticated
equipment, trained operators and are time-consuming. But, colorimetric chemosensors for the

detection of different ions pay special attention of the researchers of chemical, environmental
sciences owing to their wide range of advantages such as high selectivity, sensitivity, low
cost and direct visual detection of color change without the use of any expensive instruments
[29, 30]. Therefore, it is necessary to develop a colorimetric sensor that is capable of
recognizing both CN and Sn2+.
Schiff bases are the product of condensation reaction between the aromatic amine and
aromatic aldehyde or ketone commonly acts as an important class ligand in various metal
complexes. Moreover, due to their easy synthesis, solubility in common solvents, structural
modification, selectivity towards specific metal ion in presence of other ions due to the
unique size of the ion, charge on the metal ion and the hard-soft acid-base nature of metal and
donor atom from the Schiff base, they have been successfully used as highly selective and
sensitive sensing material for detection of ions in several optical, electrochemical or
membrane chemosensors [31, 32]. Further, Schiff bases containing salicyaldimine based
ligands in conjugation with azo chromophore can be used in the development of inexpensive
colorimetric chemosensors as they show rapid response rate, excellent color changes of the
solution and strong ability to form charge transfer complexes when they interact with cations
and anions [33].
In view of this herein we developed a colorimetric chemosensor SZ based on azo
chromophore containing Schiff-base for selective and simultaneous detection of CN and
Sn2+ in an aqueous organic medium in which CN is sensed by deprotonation of a phenolic
hydroxyl group and Sn2+ by azomethine group in Schiff base which acts as ligand towards
Sn2+. The sensor SZ detect CN and Sn2+ by a change in color from yellow to pink and
yellow to colorless respectively with high selectivity via naked eye in CH3CN/H2O (9:1, v/v)
solution among other tested ions. The interaction of SZ with CN and Sn2+ was investigated

1
using UV-Vis absorption, FT-IR, H-NMR, ESI-mass spectral techniques and theoretically
supported by Density Functional Theory (DFT) calculations.
2. Experimental
2.1. Materials and measurements
p-nitroaniline, vanillin and p-toluidine were purchased from Sigma-Aldrich and used
without further purification. Salts of different cations and anion were purchased from S. D.
Fine-Chem. Ltd. (Mumbai, India). All the analytical grade (A. R.) solvents ethyl alcohol,
acetonitrile were purchased from Research-lab fine Chem, Mumbai and Spectrochem,
1
Mumbai, India respectively and used without further purification. The H-NMR and 13C-
NMR spectra were recorded on a Bruker AC 300 MHz NMR spectrometer using DMSO-d6
as solvent and tetramethylsilane (TMS) as internal standard (δ in ppm). The elemental
analyses were performed on a Vetro-ELIII elemental analyzer. ESI-Mass spectra were
recorded on waters UPLC-TQD Mass spectrometer, UV-Vis absorption spectra were
recorded on ELICO SL-210 UV-Vis double beam spectrophotometer at room temperature
using a quartz cell with 1 cm path length, infrared (IR) spectra of sample and its complex
were recorded on a Shimadzu FTIR-8400 spectrometer and pH values were measured by
using digital pH-meter (Equip-Tronics EQ-614 A).
2.2. Synthesis of Chemosensor
In a first step diazonium salt from p-nitroaniline was prepared according to the earlier
reported method [34, 35]. Similarly, in a second flask phenolate solution of vanillin was
prepared by dissolving vanillin in NaOH and cooled to 0°C and then a solution of diazonium
salt was slowly added to the phenolate solution of vanillin placed in an ice bath with constant
stirring for about one hour and then allowed to room temperature. The precipitate formed
filtered and recrystallized in ethanol to give the desired dye (2-hydroxy-3-methoxy-5-[(E)-(4-

nitrophenyl)diazenyl]benzaldehyde). Then the prepared dye (1 mmol) and p-toluidine (1
mmol) with little quantity of acetic acid were mixed in 40 mL of hot absolute ethanol and the
resulting solution was refluxed for 9 hours at 80°C. The progress of the reaction was
monitored by using TLC (n-hexane/ethyl acetate, 2:8, v/v), after completion of the reaction,
the reaction mixture cooled to room temperature and the precipitate obtained was filtered,
washed with ethanol and recrystallized in DMF/H2O to give reddish-brown solid (Scheme 1).
1
(Yield, 74%), Melting point: >300°C; H-NMR (300 MHz, DMSO-d6) δ (ppm), (Fig. S1):
2.36 (s, 3H, –CH3), 3.73 (s, 3H, –OCH3), 7.16–7.17 (d, 2H, HAr), 7.29–7.31 (d, 2H, HAr),
7.46–7.47 (s, 1H, HAr), 8.08–8.08 (s, 1H, HAr), 8.14–8.16 (d, 2H, HAr), 8.44–8.46 (d, 2H,
13
HAr), 8.67 (s, 1H, CH), 10.58 (s, 1H, –OH); C-NMR (75 MHz, DMSO-d6) δ (ppm), (Fig.
S2): 20.9, 55.3, 99.9, 118.9, 122.8, 123.7, 123.9, 125.9, 131.4, 139.1, 146.9, 149.0, 150.3,
152.2, 157.3, 160.8; Anal. Calcd. for C21H18N4O4 (%): C 64.61, H 4.65, N 14.35. Found: C
64.76, H 4.68, N 14.57; MS (ESI-MS) m/z 391 [SZ + H]+ (Fig. S3).
Scheme 1. Synthesis of Chemosensor SZ.
2.3. Experimental procedure
The stock solution of each cation and anion were prepared at 1.0 × 102 mol/L in
MeCN: water and the stock solution of chemosensor 3 × 103 mol/L were prepared in
acetonitrile. For UV-Visible absorbance spectral measurements sensor SZ was further diluted

to 5 ml with MeCN: bis-tris buffer (9:1, v/v; pH= 7.0) to give desired concentration 30
µmol/L and then absorption spectra were recorded by adding 150 µmol/L of each ion to the
solution of SZ.
3. Result and discussion
3.1. Colorimetric sensing of anion
The chemosensing properties of chemosensor SZ (30 μmol/L) towards various anions
2
2
2

such as F, Cl, Br, I, CN, AcO, Cr2O7 , S2O8 , NO3 , SCN, H2PO4 in MeCN: bis-tris
buffer (9:1, v/v; pH= 7.0) was investigated by visible color change and UV-Vis absorption
spectral changes. As shown in Fig. 1, chemosensor SZ showed a high energy intramolecular
charge transfer absorption band located at 371 nm attributed due to π- π* transition of azo
and azomethine chromophores. Upon the addition of 150 µmol/L of each anion, SZ showed a
distinct spectral change in the absorption spectrum in the presence of CN with a naked eye
color change from yellow to pink. While other anions showed little or no absorption spectral
changes of SZ. Indicating chemosensor SZ could be served as a naked eye colorimetric
sensor for cyanide ion. This high selectivity of SZ to CN over other anions may be explained
by the basicity (pKa) and hydrogen bonding of the anions in an aqueous medium. The


basicity of the anions is supposed to be in order of CN> AcO> F> H2PO4 > Cl> HSO4 >

SCN> NO3 > Br> I and that of hydrogen bonding ability based on electronegativity is as

follows; F> AcO> H2PO4 > CN, that is in aqueous medium the hydration energy of F
(ΔHhyd = 505 kJ/mol) and AcO (ΔHhyd = 375 kJ/mol) are comparatively more than CN
(ΔHhyd = 67 kJ/mol) [36]. Hence in aqueous medium CN has weak hydrogen bonding high
basicity as compared to other anions such as F, AcO or SCN as a result, CN deprotonate
phenolic proton of SZ and showing a new charge transfer band at 488 nm.

Fig. 1 UV-Vis absorbance spectra of SZ (30 µmol/L) in presence of different anions (150
µmol/L) in MeCN: bis-tris buffer (9:1, v/v; pH= 7.0) solution.
To further study the preferential selectivity of chemosensor SZ for CN competitive
experiments was conducted in presence of various competing anions (F, Cl, Br, I, AcO
2
2
2

Cr2O7 , S2O8 , NO3 , SCN, H2PO4 ). For competitive experiment chemosensor SZ (30
μmol/L) was mixed with 150 µmol/L of CN and 150 µmol/L of other competitive anions.
The results indicate that SZ shows good selectivity for CN in the presence of coexisting
anions makes it useful in practical application for CN in the presence of coexisting anions
(Fig. 2).

Fig. 2 UV-Vis absorbance responses of SZ in absence and presence of CN ion (150 µmol/L)
and other competing anions (150 µmol/L) in MeCN: bis-tris buffer (9:1, v/v; pH= 7.0)
solution at wavelength 488 nm.
Based on the selectivity of the sensor SZ towards CN, the binding affinity of SZ (30
μmol/L) towards CN was further investigated by UV-visible titration experiment at different
concentration levels of cyanide ion. Fig. 3 shows that with the gradual addition of CN from
0.0150 µmol/L the absorption peak of SZ decreases gradually at 371 nm and a new
absorption peak emerges at 488 nm with an isosbestic point at 403 nm indicating the
formation of new intermediate in the reaction medium. Furthermore, a large red shift of 117
nm in absorption spectra of SZ led us to the transition of internal charge transfer (ICT) band
through the deprotonation phenolic OH proton attached with electron-deficient NO2 group
by the CN ion, is mainly due to the π delocalization of aromatic proton which reduces the
energy gap of p-p transition [37] results a new absorption band at 488 nm with remarkable
color change from yellow to pink.

Fig. 3 UV-visible absorbance spectral changes of SZ (30 µmol/L) with increasing
concentrations of CN in MeCN: bis-tris buffer (9:1, v/v; pH= 7.0) solution.
Also, the stoichiometry of chemosensor SZ and CN ion complex was determined by
Job’s plot method [38] by considering the sum of the concentration of CN and SZ constant
and varying the mole fraction from 0.1 to 0.9. The Job’s plot reached a maximum value at 0.5
confirming that, 1:1 stoichiometry complex between SZ and CN (Fig. S4) with binding
constant; Ka= 1.702 × 103 M1 determined by using the Benesi-Hildebrand equation (1) [39]
(Fig. S5),
1
1
1
(1)
=
+

[
)
CN
]
(
A A

Ka Amax
A
Amax A

0

0
0
Moreover, to validate the chemosensing performance of SZ in a real sample, the
experimental data obtained from UV-Vis titration for a concentration of CN were plotted to
obtain a linear relationship. Fig. S6 showed SZ gives a good linear relationship in the

calibration graph (AA0) as a function of CN concentrations at wavelength 488 nm in the
range 1.575 µmol/L with correlation coefficient 0.9972. Moreover, after the gradual
addition of 75 µmol/L of CN, no further variation is observed in the absorption spectra of
SZ indicating that the SZ reached a saturable concentration of CN (Fig. S7). Importantly,
the plot of (AA0) against the concentration of CN fit a linear Beer-Lambert equation.
The limit of detection (LOD) was calculated by equation (2) [40],
3

(2)
LOD =
k
Where σ is the standard deviation of the y-intercept of the regression line and k is the
slope of the calibration curve. Here, the colorimetric LOD for CN is 0.649 µmol/L which is
lower than the maximum permitted level of cyanide in drinking water regulated by world
health organization (1.9 μmol/L) [41].
3.2. Colorimetric sensing of cation
The colorimetric sensing study of chemosensor SZ was further carried towards
biologically important cations including (Na+, K+, Mg2+, Ca2+, Ba2+, Al3+, Sn2+, Pb2+, Fe2+,
Fe3+, Co2+, Ni2+, Cu2+, Ag+, Zn2+, Cd2+, Hg2+) by naked eye and UV-Visible absorption
spectra measurements in MeCN: bis-tris buffer (9:1, v/v; pH= 7.0). Fig. 4 shows upon the
addition of 150 µmol/L of each cation, only Sn2+ shows a significant increase in the intensity
of the absorption spectrum at 283 nm and color changes from yellow to colorless with a
hypsochromic shift. At the same experimental conditions, other cations did not induce any
spectral or color change of the SZ. Thus, sensor SZ can be used for the colorimetric detection
of Sn2+ in an organic-aqueous medium.

Fig. 4 UV-Vis absorbance spectra of SZ (30 µmol/L) in the presence of different cations (150
µmol/L) in MeCN: bis-tris buffer (9:1, v/v; pH= 7.0) solution.
To further study the selectivity of SZ as a colorimetric chemosensor for Sn2+,
competition experiments were conducted in the presence of other competitive cations. For a
competitive experiment, 30 μmol/L of sensor SZ was treated with 150 µmol/L of Sn2+ in
presence of other competitive cations (150 µmol/L). As shown in Fig. 5 no interference was
observed for the detection of Sn2+ in the presence of competitive cations. Hence, SZ shows
better selectivity over other tested competitive cations with a notable color change from
yellow to colorless.

Fig. 5 Absorbance responses of SZ in absence and presence of Sn2+ ion (150 µmol/L) and
several competing cations (150 µmol/L) in MeCN: bis-tris buffer (9:1, v/v; pH= 7.0) solution
at wavelength 283 nm.
Moreover, the UV-Vis titration experiment with different concentrations of Sn2+ ion
was conducted by using 30 μmol/L solution of SZ to examine the binding affinity of SZ with
Sn2+. Fig. 6 shows the gradual addition of Sn2+ from 0.0 to 150 µmol/L. to the solution of SZ,
absorption band emerges at 283 nm with an isosbestic point at 318 nm signifying conversion
of SZ into a single SZ Sn2+ species which may be due to the LMCT and the selectivity of
SZ to Sn2+ is according to the Pearson’s hard-soft acid-base theory [42], nitrogen from imine
(HC=N) is a middle-intensity base and Sn2+ is a soft borderline acid. Therefore, Sn2+ is likely
to form its stable complex with SZ.

Fig. 6 UV-visible absorbance spectral changes of SZ (30 µmol/L) with increasing
concentrations of Sn2+ in MeCN: bis-tris buffer (9:1, v/v; pH= 7.0) solution.
To get a clear understanding of the stoichiometry of the SZ Sn2+ complex, Job’s plot
method was conducted [38]. The Job’s plot analysis shows a maximum of 0.33 representing
2:1 stoichiometry between SZ and Sn2+ ion (Fig. S8). Besides, from the UV-Vis titration
experimental data for the concentration of Sn2+, the binding constant of SZ for Sn2+ was
estimated to be; Ka= 4.195 × 103 M1 using equation (3) (Fig. S9) [39],
1
1
1
(3)
=
+
2 +
A A

(
)
[
Sn
0
Amin A

0
]
Ka Amin
A
0

Furthermore, the LOD for Sn2+ was measured by using the formula 3σ/k is found to
be 0.754 µmol/L with correlation coefficient 0.9959.

3.3. Effect of pH
For successful practical application of chemosensor SZ, proper pH condition of the
sample solution is an important factor that affects the spectral properties of the SZ. The effect
of pH on the absorption spectrum of the SZ was studied in the pH range 212 by using bis-
tris buffer solution and the pH value of buffer solution was adjusted by mixing a diluted
solution of HCl and NaOH. The results of changes in the absorption intensity of the SZ at
488 nm and 283 nm were recorded in the presence of CN and Sn2+ ion as shown in Fig. S12.
In the presence of CN and Sn2+, SZ shows maximum and stable absorbance intensity in the
pH range 610. Therefore, the present work was carried at pH= 7.0 by using the bis-tris
buffer at room temperature.
3.4. NMR, IR and ESI-MS Studies for CN and Sn2+
1
To explore the sensing mechanism of chemosensor SZ towards CN and Sn2+, H-
1
NMR titration experiment, IR and ESI-MS studies were performed. Fig. 7 shows the H-
NMR spectra of sensor SZ in the absence and presence of CN and Sn2+ in DMSO-d6. In the
absence of CN and Sn2+, SZ shows singlet resonance peak at δ= 10.58 and 8.67 ppm for
phenolic proton and imine proton respectively. When 30 µmol/L of CN was added to the
sensor SZ, the phenolic proton peak at δ= 10.58 (s, 1H) ppm almost disappeared, and other
aromatic ring protons specifically phenyl protons possessing –OH group are involved in
delocalization show small upfield shifts. Indicates that deprotonation of phenolic –OH group
of SZ by CN may be delocalized through the whole molecule during the recognition process.
Similarly, upon the addition of 15 µmol/L of Sn2+ to sensor SZ, the phenolic –OH proton
peak at δ= 10.58 (s, 1H) ppm completely disappeared and the imine proton peak at δ= 8.67 (s,
1H) ppm shifted downfield to δ= 8.85 ppm along with marginal downfield of aromatic proton

peaks. Indicating the phenolic –OH and nitrogen (-CH=N-) of SZ takes part in the
complexation.
Fig. 7 1H-NMR spectra of SZ in absence and presence of CN and Sn2+ ion.
Furthermore, Fig. 8 shows the IR spectrum of the SZ in the absence and presence of
CN and Sn2+. In the IR spectrum of the SZ, the stretching absorption peaks of HC=N
appeared at 1624 cm1 and a broad as well as in-plane bending vibration peak of –OH
observed around at 3400 cm1 and 1320 cm1 respectively. After the interaction with CN, the

vibrational peak corresponds to the –OH proton get reduced while this spectrum shows the
stretching absorption peaks of the HC=N group. However, upon complexation with Sn2+, the
absorption vibration peaks of HC=N and –OH almost disappeared. Indicates that, CN
deprotonate the phenolic –OH group and Sn2+ had complexation with imine (HC=N) nitrogen
and phenolic –OH group of SZ. To get further information for the binding mode of the SZ
Sn2+ complex, ESI-MS study was carried out. As shown in Fig. S13, the positive ion the peak
at m/z 899 was corresponding to [2SZ+ Sn2+ 1H]+, which provides strong evidence for the
2:1 stoichiometry between SZ and Sn2+.
Fig. 8 IR spectra of chemosensor SZ, SZ CN and SZ Sn2+.
3.5. DFT Studies
In addition, to better understand the binding mode of sensor SZ with CN ions,
theoretical studies were performed by using the ORCA program package (version 3.0.3). The
geometries of SZ and SZ CN complex were optimized by using B3LYP/def2-TZVP [43,
44]. As shown in Fig. 9, the electron density of SZ at HOMO is mainly spread over the entire
molecule whereas unoccupied orbital LUMO is localized mainly on 4-[(E)-(4-

nitrophenyl)diazenyl]phenol unit. On complexation of the SZ with CN, HOMO is localized
on 4-diazenyl-2-methoxyphenol moiety and LUMO is localized on 2-methoxy-4-[(E)-(4-
nitrophenyl)diazenyl]phenol moiety. Likewise, the energy band gap (∆E) between HOMO
and LUMO of SZ and corresponding SZ CN were decreased from 3.1066 eV to 2.4657 eV
respectively. These results predicted intramolecular charge transfer from 4-diazenyl-2-
methoxyphenol to 2-methoxy-4-[(E)-(4-nitrophenyl)diazenyl] phenol moiety induced by CN
ion and is in closed agreement with the new charge transfer absorption band observed at 488
nm in the UV-Visible spectra.
Thus by considering the above results, the sensing mechanism of chemosensor SZ for
CN and Sn2+ was shown in Scheme 2 and Scheme 3.
Fig. 9 Geometry optimized structure and HOMO and LUMO energy level of (a) SZ and (b)
SZ CN.

Scheme 2. Proposed binding mode of chemosensor SZ for CN.
Scheme 3. Proposed binding mode of chemosensor SZ for Sn2+.
3.6. Applications of the proposed Chemosensor SZ
3.6.1. Solid-state detection of CN and Sn2+
To explore the practical application of SZ for quantitative, quantitative and on-site
detection of CN and Sn2+ ion the test strips of chemosensor SZ were prepared by immersing
Whatman filter paper into solution of chemosensor (1 mmol) prepared in MeCN: bis-tris
buffer (9:1, v/v, pH=7.0), dried in air and then the test strips were dipped in aqueous solution
of CN and Sn2+ prepared at different concentration. An immediate color change was
observed from yellow to pink and yellow to colorless respectively. As depicted in Fig. 10 the
expected LOD of test strip coated with SZ for CN and Sn2+ was 25 µmol/L.

Fig. 10 Photographs of the filter paper coated with SZ in different concentrations of (A) CN
and (B) Sn2+.
3.6.2. Determination of CN from industrial waste water
To check practical utility, the proposed chemosensor SZ was successfully applied for
the determination of CN in industrial waste water samples collected from Industrial estate,
Ichalkaranji (West Maharashtra, India). The collected water samples were first filtered
through Whatman No. 41 filter paper to remove suspended solid material, impurities, etc.
After that, samples were spiked with a standard solution of CN ions at two different
concentration levels and finally diluted within the working linear range and examined with
the proposed method by standard addition method [40, 45]. The results are summarized in
Table 1 which shows that the chemosensor SZ can measure the concentration of CN in
water samples with good recoveries in the range of 101.23% and 102.19%. Hence, the
chemosensor SZ can be applicable for CN determinations in different water samples.

Table 1: Determination of CN in industrial wastewater samples via a standard addition
method (n=3).
Amount of
Standard
CN Added
(µmol/L)
Recovery
of CN
added
Total CN
found (n=3)
(µmol/L)
Relative
Error
(%)
Name of the
sample
RSD
(%)
(n=3) (%)
Industrial
waste-water I
20.0
30.0
20.0
30.0
20.27
30.32
20.36
30.77
101.39
101.06
101.81
102.57
0.85
0.85
0.71
0.61
1.39
1.06
1.81
2.57
Industrial
waste-water II
Industrial estate, Ichalkaranji (West Maharashtra, India)
4. Conclusions
In conclusion, we have developed a simple and cost-effective azo linked Schiff base
as a colorimetric chemosensor (SZ) for selective detection of CN and Sn2+ over other
competitive ions in CH3CN: bis-tris buffer (9:1, v/v) medium. SZ displayed remarkable
changes in absorption band and significant color change in the presence of CN and Sn2+ with
detection limit 0.649 µmol/L and 0.754 µmol/L respectively. Binding mechanism of SZ for
1
CN and Sn2+ was studied by H-NMR, IR and ESI-MS studies. Furthermore, DFT studies
were supported the experimental result and sensing mechanism for CN is due to ICT.
Importantly, chemosensor SZ was also successfully applied for quantitative detection of CN
in an industrial wastewater sample and colorimetric test kit was designed for quantitative and
onsite detection of CN and Sn2+.
Acknowledgments
Authors are thankful to Shivraj College, Gadhinglaj, Department of Chemistry;
Shivaji University, Kolhapur and SAIF CSIR-CDRI, Lucknow, India for providing the all

necessary infrastructural and instrumental facility. One of the author AHG gratefully
acknowledges DST-SERB, New Delhi for providing research grants under young scientist
scheme (File no. YSS/2015/001806).
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Graphical abstract:

[46]
Highlights:

A new colorimetric chemosensor (SZ) based on azo chromophore containing Schiff base.

Chemosensor exhibited dual ions selectivity towards CN and Sn2+ over other coexisting ions
with lowest limit of detection.



The experimental results theoretically supported by DFT studies.
Test strips coated with SZ can easily detect CN and Sn2+ ion in aqueous solutions.
Chemosensor was successfully used for quantitative and onsite detection of CN and Sn2+.
[47]