N1,N2-Bis[1-(2-hydroxyphenyl)methylidene] ethanedihydrazide as a neutral ionophore for preparation of a new Ho 3+ PVC-membrane sensor

Article abstract of DOI:10.1016/j.cclet.2010.10.056

N¹,N²-Bis[1-(2-hydroxyphenyl)methylidene] ethanedihydrazide (MEH) was used as new compound which plays the role of an excellent ion carrier in the fabrication of a Ho(III) membrane electrode. The electrode shows a good selectivity fo

Full text of DOI:10.1016/j.cclet.2010.10.056

Available online at www.sciencedirect.com
Chinese Chemical Letters 22 (2011) 701–704
www.elsevier.com/locate/cclet
1
N ,N -Bis[1-(2-hydroxyphenyl)methylidene]ethanedihydrazide as a
2
neutral ionophore for preparation of a new
3
+
Ho PVC-membrane sensor
Hassan Ali Zamani
Department of Applied Chemistry, Quchan branch, Islamic Azad University, Quchan, Iran
Received 25 September 2010
Abstract
1
2
N ,N -Bis[1-(2-hydroxyphenyl)methylidene]ethanedihydrazide (MEH) was used as new compound which plays the role of an
excellent ion carrier in the fabrication of a Ho(III) membrane electrode. The electrode shows a good selectivity for Ho(III) ion with
respect to most common cations including alkali, alkaline earth, transition and heavy metal ions. This electrode has a wide linear
ꢁ
6
ꢁ2
dynamic range from 1.0 ꢀ 10 to 1.0 ꢀ 10 mol/L with a Nernstian slope of 19.8 ꢂ 0.3 mV per decade and a low detection limit
ꢁ
7
of 5.8 ꢀ 10 mol/L in the pH range of 2.5–9.8, while the response time was rapid (<10 s). The suggested sensor was applied to the
determination of Ho(III) ions in tap water and river water samples.
#
2010 Hassan Ali Zamani. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Ion-selective electrode; Potentiometry; Sensor; PVC membrane
The determination of individual rare earth elements (REEs) in their mixtures is still very difficult because they are
so similar in nature. Many techniques have been developed in order to determine the value of Ho(III) in real samples
such as: inductively coupled plasma atomic emission spectroscopy and neutron activation analysis. But almost all of
them are expensive and time consuming. In this report we are going to introduce a new simple and non-expensive
1
2
method which is based on an electrochemical sensor with a sensitive and selective component N ,N -bis[1-(2-
hydroxyphenyl)methylidene]ethanedihydrazide (MEH) (Fig. 1). This sensor has relatively high selectivity and low
detection limit relative to the other sensor which has been developed for determination of one of lanthanides even in
presence of other lanthanides. There are a few reports on holmium potentiometric sensors [1–4].
Reagent grade nitrobenzene (NB), dibutyl phthalate (DBP), benzyl acetate (BA), acetophenone (AP), high relative
molecular weight PVC, sodium tetraphenyl borate (NaTPB), tetrahydrofurane (THF) and chloride and nitrate salts of
the cations used were purchased from Merck and Aldrich and used as received. All solutions were prepared using
doubly distilled deionized water.
The salycilaldehayde (2 mmol, 0.244 g) was dissolved in hot ethanol. Then, the oxalohydrazide (1 mmol, 0.118 g)
was added to the solution. The obtained mixture was refluxed for 1 h. Then, the solid product was crystallized in
solution of acetone and ethanol (1:1).
E-mail address: haszamani@yahoo.com.
1001-8417/$ – see front matter # 2010 Hassan Ali Zamani. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2010.10.056

[()TD$FIG]
7
02
H.A. Zamani / Chinese Chemical Letters 22 (2011) 701–704
OH
HO
O
N
NH
NH
N
O
Fig. 1. The MEH structure.
The required amounts of the membrane ingredients (30 mg powdered PVC and 66 mg NB as plasticizer) were
mixed and dissolved in 5 mL of THF. To this mixture, 2 mg NaTPB and 2 mg ionophore MEH were added and the
solution was mixed well. The resulting mixture was transferred into a glass dish of 2 cm in diameter. The THF content
of the mixture was evaporated slowly, until an oily concentrated mixture was obtained. A Pyrex tube (3–5 mm in
diameter) was dipped into the mixture for about 10 s, so that a transparent membrane of about 0.3 mm in thickness was
formed. Afterwards, the tube was removed from the solution kept at room temperature for 12 h and filled with an
ꢁ
3
internal solution (1.0 ꢀ 10 mol/L HoCl ) [5–13]. The electrode was finally conditioned for 36 h by soaking in a
3
ꢁ
3
1
.0 ꢀ 10 mol/L solution of HoCl . A silver/silver chloride coated wire was used as an internal reference electrode.
3
The emf measurements with the polymeric membrane were carried out with the following cell assemblies: Ag–
ꢁ
3
AgClj1.0 ꢀ 10 mol/L HoCl jPVC membrane: test solutionjHg–Hg Cl , KCl (satd).
3
2
2
A Corning ion analyser 250 pH/mV meter was used for the potential measurements at 25.0 8C. The activities were
calculated according to the Debye–Huckel procedure [14].
In order to check selectivity of MEH toward lanthanide cations, MEH was used as a neutral carrier to prepare the
PVC membrane ion-selective electrodes for a wide variety of cations, including alkali, alkaline earth, transition and
heavy metal ions and the corresponding resulting data are listed in Fig. 2. The respective potential responses of the
most sensitive ion-selective MEH-based electrodes clearly exhibited that only the Ho(III) ion illustrated a strong
response (with a slope of 19.8 ꢂ 0.3 mV per decade) to the MEH-based membrane sensors in comparison with the
3
+
other tested cations. This observation is most probably due to the proper size of Ho ion to the semi cavity of flexible
3
MEH, and the rapid exchange kinetics of the resulting MEH–Ho complex.
+
Because the degree of sensitivity and selectivity for a certain electrode is greatly related to the membrane
ingredients [15–17], the influence of the membrane composition on the potential responses of the Ho(III) sensor was
inspected. The corresponding results are provided in Table 1. The effect of the nature and the amount of the plasticizer,
3
+
the amount of PVC and the additive on the potential response of the developed Ho electrode were investigated. The
best performance was obtained with a membrane composition of 30% PVC, 66% NB, 2% MEH and 2% NaTPB.
[()TD$FIG]
Fig. 2. Potential responses of various ion-selective electrodes based on MEH.

H.A. Zamani / Chinese Chemical Letters 22 (2011) 701–704
703
Table 1
Optimization of the membrane ingredients.
No.
1
Composition (wt %)
Linear range (mol/L)
Slope (mV/decade)
PVC
30
Plasticizer
MEH
2
NaTPB
2
ꢁ
6
NB, 66
1.0 ꢀ 10
19.8 ꢂ 0.3
ꢁ
2
–
1.0 ꢀ 10
ꢁ6
ꢁ2
ꢁ2
ꢁ2
ꢁ2
ꢁ2
ꢁ2
ꢁ2
ꢁ2
2
3
4
5
6
7
8
9
30
30
30
30
30
30
30
30
DBP, 66
AP, 66
BA, 66
NB, 68
NB, 67
NB, 65
NB, 67
NB, 65
2
2
2
2
2
2
1
3
2
2
2
0
1
3
2
2
1.0 ꢀ 10 –1.0 ꢀ 10
17.3 ꢂ 0.3
18.6 ꢂ 0.5
17.7 ꢂ 0.2
12.4 ꢂ 0.4
17.8 ꢂ 0.5
18.5 ꢂ 0.6
17.3 ꢂ 0.5
18.3 ꢂ 0.3
ꢁ6
1.0 ꢀ 10 –1.0 ꢀ 10
ꢁ6
1.0 ꢀ 10 –1.0 ꢀ 10
ꢁ6
1.0 ꢀ 10 –1.0 ꢀ 10
ꢁ6
1.0 ꢀ 10 –1.0 ꢀ 10
ꢁ6
1.0 ꢀ 10 –1.0 ꢀ 10
ꢁ6
1.0 ꢀ 10 –1.0 ꢀ 10
ꢁ6
1.0 ꢀ 10 –1.0 ꢀ 10
The emf response of the polymeric membrane indicated a Nernstian slope of 19.8 ꢂ 0.3 mV per decade across an
ꢁ
6
ꢁ2
extended holmium concentration range from 1.0 ꢀ 10 to 1.0 ꢀ 10 mol/L. The limit of detection, as determined
ꢁ
7
from the intersection of the two extrapolated segments of the calibration graph, was 5.8 ꢀ 10 mol/L.
ꢁ
3
The pH dependence of the responses of the membrane was investigated by the sensor behavior in a 1.0 ꢀ 10 mol/
3
+
L Ho solution, while varying the solution pH in a range of 2.0–12.0. The potential response of the sensor is
independent of pH, in the pH range of 2.5–9.8. There are, however, potential changes at pH values that are out of this
range. The potential decrease at higher pH values (>9.8), is due to the formation of insoluble of Ho(OH) , while the
3
observed increases in the potential response of the sensor, at lower pH values (<2.5), is most probably due to the
responds of the sensor to the hydrogen ions (protonation of nitrogen atoms of ion carrier).
ꢁ
3
The pH dependence of the responses of the membrane was investigated by the sensor behavior in a 1.0 ꢀ 10 mol/
3
+
L Ho solution, while varying the solution pH in a range of 2.0–12.0. The potential response of the sensor is
independent of pH, in the pH range of 2.5–9.8. There are, however, potential changes at pH values that are out of this
range. The potential decrease at higher pH values (>9.8), is due to the formation of insoluble of Ho(OH) , while the
3
observed increases in the potential response of the sensor, at lower pH values (<2.5), is most probably due to the
responds of the sensor to the hydrogen ions (protonation of nitrogen atoms of ion carrier).
Table 2
3
Comparison of selectivity coefficients, detection limit, response time and linearity range of the developed Ho sensor and the formerly mentioned
+
3
Ho ion-selective electrodes.
+
Ref. [1]
Ref. [2]
Ref. [3]
Ref. [4]
This work
ꢁ5
ꢁ2
ꢁ6
ꢁ6
ꢁ2
ꢁ7
ꢁ5
ꢁ2
ꢁ6
ꢁ5
ꢁ2
ꢁ6
ꢁ6
ꢁ2
ꢁ7
Linearity range
1.0 ꢀ 10
1.0 ꢀ 10
7.0 ꢀ 10
–
1.0 ꢀ 10
1.0 ꢀ 10
8.5 ꢀ 10
–
1.0 ꢀ 10
1.0 ꢀ 10
8.0 ꢀ 10
–
2.0 ꢀ 10
1.0 ꢀ 10
5.0 ꢀ 10
–
1.0 ꢀ 10
1.0 ꢀ 10
5.8 ꢀ 10
–
(
mol/L)
Detection limit
mol/L)
(
Response time (s)
Selectivity
<15
MPM
<15
MPM
ꢃ5
ꢃ5
<10
MPM
MPM
MPM
coefficients
+
ꢁ3
ꢁ2
ꢁ3
ꢁ2
ꢁ4
ꢁ4
ꢁ3
ꢁ3
ꢁ4
ꢁ4
ꢁ3
ꢁ3
ꢁ3
ꢁ3
ꢁ3
ꢁ3
ꢁ3
ꢁ3
ꢁ4
ꢁ3
ꢁ3
ꢁ3
ꢁ4
ꢁ4
ꢁ3
ꢁ4
ꢁ4
ꢁ3
ꢁ4
ꢁ4
K
7.0 ꢀ 10
6.7 ꢀ 10
5.9 ꢀ 10
3.3 ꢀ 10
7.4 ꢀ 10
7.5 ꢀ 10
8.5 ꢀ 10
–
7.0 ꢀ 10
3.0 ꢀ 10
7.2 ꢀ 10
2.5 ꢀ 10
2.4 ꢀ 10
6.4 ꢀ 10
6.7 ꢀ 10
5.3 ꢀ 10
2.8 ꢀ 10
8.5 ꢀ 10
8.8 ꢀ 10
4.2 ꢀ 10
9.3 ꢀ 10
9.4 ꢀ 10
+
Na
4.0 ꢀ 10
6.5 ꢀ 10
3.0 ꢀ 10
2
+
Ca
8.5 ꢀ 10
3.2 ꢀ 10
1.2 ꢀ 10
2
+
Pb
4.5 ꢀ 10
6.7 ꢀ 10
7.5 ꢀ 10
2
+
Co
–
–
–
2
+
Ni
Cr
Fe
La
–
–
–
3
3
+
+
–
–
–
–
–
–
–
3
+
ꢁ2
ꢁ3
ꢁ3
ꢁ4
ꢁ3
ꢁ2
ꢁ3
ꢁ3
ꢁ3
ꢁ3
1.0 ꢀ 10
4.0 ꢀ 10
6.5 ꢀ 10
–
8.7 ꢀ 10
–
1.3 ꢀ 10
3.5 ꢀ 10
2.0 ꢀ 10
–
3.0 ꢀ 10
3.0 ꢀ 10
1.5 ꢀ 10
–
3
+
Er
3
+
Tm
–
3
+
ꢁ3
Yb
4.2 ꢀ 10

704
H.A. Zamani / Chinese Chemical Letters 22 (2011) 701–704
Table 3
Determination of Ho spiked in tap and river water samples by use of the proposed electrode.
3
+
3
+
Sample
Ho added (mg/mL)
Found (mg/mL)
Recovery (%)
a
River water
0.25
(0.28 ꢂ 0.04)
112
108
0
.5
0.25
.5
(0.54 ꢂ 0.04)
Tap water
(0.29 ꢂ 0.02)
116
106
0
(0.53 ꢂ 0.04)
a
Results are based on three measurements.
For analytical applications, dynamic response time is very important for any sensor. The dynamic response time of
ꢁ
6
ꢁ2
the membrane was measured at various concentrations (1.0 ꢀ 10 –1.0 ꢀ 10 mol/L) of the test solutions. In the
whole concentration range the electrode reaches its equilibrium response, very fast (<10 s).
Potentiometric selectivity coefficient is one of the most important characteristics of any membrane sensor. In this
3
+
research, the potential responses of the recommended Ho membrane sensor to a wide variety of cations were
investigated by matched potential method (MPM) [18,19]. The selectivity coefficients for the monovalent tested
+
+
ꢁ3
cations (Na , K ) are smaller than 2.5 ꢀ 10 . Additionally, the selectivity coefficients for the divalent tried cations
2
+
2+
2+
2+
ꢁ4
ꢁ3
3+
(
Ca , Co , Ni , Pb ) are also small in the range of 5.3 ꢀ 10 –6.4 ꢀ 10 . In the case of trivalent cations (Yb ,
3
+
3+
3+
3+
3+
ꢁ4 ꢁ3
Er , Tm , La , Cr , Fe ), the selectivity coefficients are relatively small (from 8.5 ꢀ 10 to 4.2 ꢀ 10 ).
Eventually, it can be stated that because of the good selectivity coefficients values, the disturbance produced by these
cations in the function of the developed membrane sensor is negligible.
Table 2 compares the selectivity coefficients, detection limit, response time and linearity range of the Ho(III) sensor
with those of the best previously Ho(III) electrodes reported in the literature by other researchers [1–4]. As it is
obvious, the selectivity coefficient of the electrode for all tried cations is superior in respect with the coefficients of the
best previously reported holmium sensors.
3
+
The optimized sensor was successfully applied to the determination of Ho ions in tap water and river water
samples. The results of triplicate measurements are summarized in Table 3. As can be seen from Table 3, the amounts
of the holmium ions, which were added to the water sample solutions (0.25–0.5 mg/mL), could be determined by the
sensor with relatively good accuracy.
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