J Fluoresc
Fig. 7 Color changes of the filter
paper containing chemosensor 1
treated with various anions
v) at room temperature. The optical absorbance of
chemosensor 1 with CN¯ (Fig. 3) was not influenced by the
subsequent addition of competing anions, which indicated that
chemosensor 1 had shown specific selectivity for CN¯
maximum absorbance was observed at about 0.7 mol fraction
of [CN¯]/[CN¯] + [sensor], suggesting a 1:2 stoichiometry
ratio between the chemosensor 1 and cyanide ion.
The proposed reaction mechanism was shown in Scheme
2. Investigating the recognition mechanism indicated that
CN¯ is expected to be detectable by nucleophilic attack to-
ward the carbon atom of the C = C group, which is activated
by the powerful electron-withdrawing feature of cyanide
groups. The results confirmed a 1:2 stoichiometry between
chemosensor 1 and CN¯ ions. Furthermore, compound 7
was previously synthesized and characterized by Bock and
co-workers [33]. The properties of compound 7 completely
correspond to the Bock’s compound; its Mass spectrum and
the proposed fragmentations are presented in Fig. 6 and
Scheme 3, respectively.
To evaluate the influence of CN¯ concentrations on the
UV-Vis absorption of the chemosensor 1, titration experiment
was carried out in DMSO/EtOH (1:9, v/v) solution with dif-
ferent concentrations of CN¯. As shown in Fig. 4, the absor-
bance of chemosensor 1 increases gradually upon addition of
different amounts of CN¯. The Fig. 4 inset shows two good
linear relations between the absorbance at 567 nm and the
concentration of CN¯ with the linear equation of
4
Absorbance = 1.465 × 10 [CN¯] + 0.0114 in the equivalent
2
ranges from 0 to 0.8 with regression coefficient of R = 0.939,
4
and the linear equation of Absorbance = 6.326 × 10 [CN¯]-
0
.3761 in the equivalent ranges from 0.8 to 1.8 with
2
R = 0.9923. The detection limit (DL) of chemosensor 1 as a
colorimetric sensor for the analysis of CN¯ was also deter-
mined by the following equation:
Filter Paper Test
To assess the practical applicability of chemosensor 1, a pre-
liminary paper test strip system was constructed as shown in
Fig. 7. The neutral filter papers were immersed into the solu-
tion of chemosensor 1 (500 mM) and dried in air. Then, the
prepared test papers were dipped into the various solutions of
anions. Only CN¯ changed the color from light yellow to
purple. This phenomenon demonstrated that chemosensor 1
could be used as a simple and useful paper test for the rapid
detecting CN¯.
KSd
DL ¼
m
Where S is standard deviation of blank solution measured
d
six times, m is the slope of the absorbance versus CN¯ con-
centration; and K is confident level which is generally set to 3.
Therefore, the colorimetric DL of Chemosensor 1 for CN¯
ions was tested by absorption changes was calculated to be
.07 × 10− M (0.3 μM, 0.03 ppm). According to the standard
7
Conclusion
3
of World Health Organization (WHO), the highest allowable
level of cyanide in drinking water should not be more than
In conclusion, we have successfully synthesized a highly sen-
sitive and specific colorimetric chemosensor 1 for cyanide ion.
It showed high selectivity towards CN¯ against various com-
1
.9 μM [35] and the US Environmental Protection Agency
(
(
EPA) has established the Maximum Contaminant Level
MCL) for cyanide in drinking water to be 0.2 ppm [36].
2
−
peting anions such as F¯, Cl¯, Br¯, I¯, CO , HCO ¯,
3
3
2
−
2−
Importantly, the chemosensor 1 is a high selective and sensi-
tive cyanide sensor which its detection limit is much lower
than that mentioned in guidelines of the WHO.
To confirm the stoichiometry of a binding between
chemosensor 1 and cyanide ion, Job’s plot analysis was di-
rected in DMSO/EtOH (1:9, v/v) solution (Fig. 5). The
CH COO¯, SO , S O , NO ¯, NO ¯, H PO ¯, and
3 4 2 3 2 3 2 4
SCN¯. Moreover, the detection limit of the chemosensor 1
-
7
toward CN¯ was 3.07 × 10 M. The colorimetric
chemosensing study showed that the chemosensor 1 is able
to detect various values of cyanide ions by the Bnaked-eye^
with a visible color change. Additionally, the color intensity of