A highly selective colorimetric chemosensor for detection of iodide ions in aqueous solution

Article abstract of DOI:10.1039/c6ra18490a

We synthesized a new iodide ion (I^-) chemosensor (CS) based on a hydrazone derivative obtained from the condensation of 2-hydroxy-1-naphthaldehyde and 2,4-dinitrophenylhydrazine. The CS showed selective colorimetric recognition of I^-

Full text of DOI:10.1039/c6ra18490a

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A highly selective colorimetric chemosensor for
detection of iodide ions in aqueous solution†
Cite this: RSC Adv., 2016, 6, 86627
*
Jie Chen, Qi Lin, Qiao Li, Wen-Ting Li, You-Ming Zhang and Tai-Bao Wei
We synthesized a new iodide ion (Iꢀ) chemosensor (CS) based on a hydrazone derivative obtained from the
condensation of 2-hydroxy-1-naphthaldehyde and 2,4-dinitrophenylhydrazine. The CS showed selective
colorimetric recognition of Iꢀ, the miscellaneous competitive anions (Fꢀ, Clꢀ, Brꢀ, HSO4ꢀ, CH3COOꢀ,
Received 20th July 2016
Accepted 30th August 2016
H2PO4ꢀ, SCNꢀ, CNꢀ, ClO4 and Sꢀ) did not lead to any significant interference. The detection limits of
ꢀ
the CS for Iꢀ is 1.1 ꢁ 10ꢀ6 M. The sensor has been successfully applied to estimate the content of iodide
ions in urine. Moreover, ion test strips based on CS were fabricated, which could act as a convenient and
efficient Iꢀ test kit for “in-the-field” measurement of iodide ions.
DOI: 10.1039/c6ra18490a
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The selective sensing of important anions is highly signicant radius, low charge density and low hydrogen bonding ability,
because anions are widely distributed and play important roles iodide is the most difficult halide to be sensed. Therefore, the
in both environmental and life sciences.1–7 Many efforts have development of chemosensors for iodide based on hydrogen-
been made to desꢀign chemosensors for anions such as Fꢀ, CNꢀ, bonding is very difficult, even that in aqueous solution.
Clꢀ, H2PO4ꢀ, SO4 , AcOꢀ, etc.8–19 However, most of the synthetic
In view of these, and as an research interesting in ions
receptors operate in nonprotonic organic solvents while few in recognition,40–42 herein, we report a new iodide ions (Iꢀ) che-
aqueous solution, and they oen require convoluted and time- mosensor (CS) based-on a hydrazone derivative obtained from
consuming syntheses.20–24 It is particularly difficult to develop the condensation of 2-hydroxy-1-naphthaldehyde and 2,4-dini-
anion recognition systems that form hydrogen bonded trophenylhydrazine (Scheme 1). In order to achieve the “naked-
complexes in aqueous solvent, for the obvious reason that the eye” detection for Iꢀ stimuli, the 2,4-dinitrophenyl hydrazone
water competes strongly for the hydrogen bonding sites.
moiety was introduced into the CS as the signal groups as well
Iodine, as we know, is a crucial trace element on earth and as binding sites. The chemosensor CS can optically and visually
mainly exists in seawater. Iodide is known an essential nutrient detect the presence of iodide over a wide range of other
in the human body.25 Iodine exists in the human body competent ions in an aqueous medium with high selectivity.
predominantly in the form of iodide (Iꢀ), which is the bio-
The sensing abilities of CS toward various anions (Fꢀ, Clꢀ,
available form of iodine for thyroid.26 As a major portion of Brꢀ, Iꢀ, HSO4ꢀ, CH3COOꢀ, H2PO4ꢀ, SCNꢀ, CNꢀ, ClO4ꢀ and Sꢀ)
iodine absorbed by the body is excreted in the urine, it acts as were investigated by UV-vis spectroscopy. When 50 equivalents
a sensitive marker of iodine intake in the body and iodine status of these anions were added to the DMSO/H2O (9 : 1, v/v)
change can be monitored through urine analysis. In addition,
elemental iodine is used in a variety of applications, for example
manufacturing of dyes, synthesis of some organic chemicals,
and in medicine.27 Therefore, it is of great importance to realize
rapid, sensitive, and selective detection of iodide in food,
pharmaceutical products, and biological samples such as urine.
Nowadays, various methods based on different principles have
Scheme 1 Structure and synthesis of the sensor CS.
been proposed to detect and determine iodide ions, including
ion chromatography,28,29 electrochemistry,30–32 and organic
chromophores or uorophores.33–39 Due to the large ionic
Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of Education
of China, Key Laboratory of Polymer Materials of Gansu Province, College of Chemistry
and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu, 730070, P.
Fig. 1 Color changes of CS (2 ꢁ 10ꢀ5 M) after addition of 50 equiva-
R. China. E-mail: weitaibao@126.com; zhangnwnu@126.com; Fax: +86 9317973191;
Tel: +86 9317973191
lents of various anions in DMSO/H2O (9 : 1, v/v). From left to right: only
CS, Iꢀ, Fꢀ, Clꢀ, Brꢀ, AcOꢀ, H2PO4ꢀ, HSO4ꢀ, ClO4ꢀ, SCNꢀ, CNꢀ and S2ꢀ
.
† Electronic supplementary information (ESI) available: Complete experimental
procedures and some of the spectroscopic. See DOI: 10.1039/c6ra18490a
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solutions of CS (2 ꢁ 10ꢀ5 M), respectively, at room temperature,
Fig. 4 shows the family of absorption spectra obtained over
a dramatic color change from purple to yellow was observed by the course of the titration of sensor CS with Iꢀ (0.1 M) in DMSO/
the naked eye only upon the addition of Iꢀ to sensor CS (Fig. 1). H2O (9 : 1, v/v). With the gradual addition of Iꢀ to sensor CS, the
An important feature of the sensor is its specic selectivity intensity of absorption bands at 424 nm increased, while the
toward the analyte over other competitive species. The varia- absorption band at 520 nm began to decrease until it reached
tions of UV-vis absorbance of CS in DMSO/H2O binary solutions a limiting value. Moreover the presence of one isosbestic points
caused by the anioꢀns (Fꢀ, Clꢀ, Brꢀ, HSO4ꢀ, CH3COOꢀ, H2PO4
,
at 461 nm indicated that sensor CS reacts with Iꢀ to form
ꢀ
SCNꢀ, CNꢀ, ClO4 and S2ꢀ) were recorded in Fig. 2. More a stable complex. The association constant (Ka) of CS with Iꢀ
importantly, chloride, bromide, and iodide have a relatively was determined using the Benesi–Hildebrand equation.45–47 The
high free energy of solvation, which indicates that the receptors measured absorbance [1/(AꢀA0)] varied as a function of 1/[Iꢀ] in
have to compete with the medium effectively.43,44 The results a linear relationship (R2 ¼ 0.9919) in Fig. 5. The association
revealed that bromide and chloride did not exhibit any obvious constant of CS with Iꢀ in DMSO/H2O (9 : 1, v/v) was calculated to
color spectral changes. Other anions exerted no inuence be 1.53 ꢁ 106 Mꢀ1. The detection limit of the absorption spec-
detection of iodide in the absorbance at 424 nm. In the presence tral changes calculated on the basis of 3s/S was 1.1 ꢁ 10ꢀ6 M for
of these ions, Iꢀ still produced similar color and optical spectral the Iꢀ.48 As shown in Fig. 6, the minimum concentration of Iꢀ
changes (Fig. 3). The results showed that sensor CS selectivity for the color change observed by the naked eye was 1 ꢁ 10ꢀ4 M.
toward Iꢀ was not affected by the presence of other anions.
To further demonstrate the potential of CS probe for prac-
tical applications, we exemplied its ability to detect Iꢀ ions in
urine samples to realize its applicability in real sample analysis.
Urine samples that were obtained from Lanzhou University
Affiliated Hospital. For the urine samples, 2 ml of acetonitrile
Fig. 2 Changes in the UV/vis spectra of CS (2 ꢁ 10ꢀ5 M) after addition
of 50 equivalents of various anions in DMSO/H2O (9 : 1, v/v).
Fig. 4 UV-vis spectra of CS (2 ꢁ 10ꢀ5 M) in DMSO/H2O (9 : 1, v/v)
upon adding an increasing concentration of Iꢀ (0.1 M).
Fig. 3 Absorbance responses of CS (2 ꢁ 10ꢀ5 M) after addition of 50
equivalents of various anions in DMSO/H2O (9 : 1, v/v) in the presence
of 50 equivalents of Iꢀ with 50 equivalents of various anions ions in
DMSO/H2O (9 : 1, v/v). Bars represent absorbance at 424 nm. The
black bars represent the addition of the competing anions ions to the
solution of CS. The red bars represent the addition of competing Fig. 5 Plot of the intensity at 424 nm for a mixture of CS (2 ꢁ 10ꢀ5 M)
anions ions and Iꢀ to the solution of CS.
in DMSO/H2O (9 : 1, v/v) and Iꢀ in H2O.
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Fig. 6 Naked-eye detection limit.
Table 1 Determination of iodide content in urine samples (n¼3)
Urine
Amount of Iꢀ
Adding I Foumd Recovery RSD
sample before adding Iꢀ (mM)
(mM)
(%)
(n ¼ 3, %)
Fig. 8 IR spectra of compound CS and CS–Iꢀ in KBr disks.
1
2
—
—
20
50
21.2
52.2
106
104
0.93
1.3
indicated that the N–H group and the H–C]N group formed
Iꢀ/H–C]N and N–H/Iꢀ hydrogen bond (Scheme 2).
and 6 ml of deionized water were added along with 2 ml urine in
centrifuge tubes. The tubes were vortex for 2 minutes and
centrifuged at 1500 rpm for 20 minutes. The supernatant of
these solutions were taken and ltered through 0.22 mm
membrane prior to use. Urine samples were analyzed using the
standard addition method. The results show an average
recovery of 105% with Relative Standard Deviation (RSD) of
1.12% for urine samples (Table 1). The experimental results
indicate that the sensor possessed excellent applicability for
real sample analysis. The development of a “dip-sticks”
approach was extremely attractive for “in-the-eld” measure-
ments that did not require any additional equipment. The test
strips were prepared by immersing lter papers into a DMSO/
H2O (9 : 1, v/v) solution of CS (1 ꢁ 10ꢀ3 M) then drying in air. As
shown in Fig. 7, when the different amount of Iꢀ (5 ꢁ 10ꢀ3 M, 1
ꢁ 10ꢀ2 M, 2 ꢁ 10ꢀ2 M) was added on the test kits, the obvious
color changes from purple to yellow were observed. Therefore,
the test strips of CS have excellent application value in the
detection of Iꢀ.
As shown in Fig. 9, before the addition of Iꢀ, there were two
intramolecular hydrogen bonds in the molecular structure of
CS. The formation of these hydrogen bonds led to the 1H NMR
chemical shis of –OH, N–H and HC]N appeared at 11.80,
11.10 and 9.59 ppm, respectively. Upon gradual addition of Iꢀ,
the –OH peak at 11.80 ppm and N–H 11.10 ppm became broad.
At the same time, the HC]N peak at 9.59 ppm decreased
gradually that is ascribed to the molecular structure underwent
an intramolecular rotation, which induced the breaking of
1
To explore the sensing mechanism of CS to Iꢀ, the IR, H
NMR titration and ESI-MS were investigated, which illustrated
the characteristic structural changes occurring upon interaction
with Iꢀ. In the IR spectra of CS, the stretching vibration
Scheme 2 A possible sensing mechanism of the sensor CS to Iꢀ.
absorption peaks of N–H, and H–C]N appeared at 3267 cmꢀ1
,
1612 cmꢀ1 respectively. However, when CS coordinated with Iꢀ,
the stretching vibration absorption peaks of N–H shied to
2960 cmꢀ1, while, the stretching vibration absorption peaks of
H–C]N shied to 1619 cmꢀ1 (Fig. 8). These phenomena
Fig. 7 Photographs of test strips (a): only CS, (b) CS + Iꢀ (5 ꢁ 10ꢀ3 M) Fig. 9 Partial 1H NMR spectra of CS (0.01 M) in DMSO upon addition of
(c) CS + Iꢀ (1 ꢁ 10ꢀ2 M) (d) CS + Iꢀ (2 ꢁ 10ꢀ2 M).
Iꢀ.
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