The new leaed (ii) ion selective electrode on free plasticizer film of pthfa photopolymer

Journal of The Electrochemical Society, 166 (15) B1513-B1519 (2019) B1513
0013-4651/2019/166(15)/B1513/7/$38.00 © The Electrochemical Society
The New Lead (II) Ion Selective Electrode Based On Free
Plasticizer Film of pTHFA Photopolymer
Sagir Alva, 1,z
Arsyad Widinugroho,1
Melny Adrian,1
Deni Shidqi Khaerudini, 1,2
Swandya Eka Pratiwi,1
and Aiman Sajidah Abd Aziz3
1Mechanical Engineering Department, Universitas Mercu Buana, West Jakarta 11650, Indonesia
2Research Center for Physics, Indonesian Institute of Science (LIPI) Kawasan Puspiptek, Serpong, South Tangerang
15314, Indonesia
3Flexible Electronics Lab, MIMOS Semiconductor Sdn. Bhd., 57000 Kuala Lumpur, Malaysia
This research has succeeded in developing a Lead (II) –Ion-selective electrode (Pb2+-ISE) sensor based on poly-tetrahydro furfuryl
acrylate (pTHFA) films free plasticizers utilizing photo-polymer technique. The Pb2+-ISE has a performance that includes a linear
range of 0.1–10−5 M, Nernstian number 26.5–29.8 mV/dec and LOD 3.24–3.98 (× 10−6) M, where the optimum composition
between KTpClPB lipophilic salt with leads (IV) ionophore is 1:1 mole ratio. The Pb2+-ISE sensor also shows a relatively good
selectivity value (Log Kpot
a,b) against several interfering ions including K+ −6.5 ± 0.3, Na+ −6.2 ± 0.1, NH4
+ −6.7 ± 0.1, Mg2+
−12.7 ± 0.2, Cu2+ −4.2 ± 0.5 and Cd2+ −6.1 ± 0.2, where the response of the Pb2+-ISE sensor is stable at pH 3–8. In this
study, the Pb2+-ISE sensor shows validation test results that are comparable to measurements using atomic absorption spectroscopy
(AAS) devices using artificial solutions and real sample. The results of testing with artificial solutions successively produced Pb2+
concentrations of 9.5 ± 0.3, 52.5 ± 1.7, and 100.8 ± 2.5 ppm, while for real samples the Cisadane river was 0.0025 ± 0.45 ppm and
the refueling station was 18.15 ± 16.74 mg/kg soil sample.
© 2019 The Electrochemical Society. [DOI: 10.1149/2.0601915jes]
Manuscript submitted August 19, 2019; revised manuscript received October 15, 2019. Published November 4, 2019.
The development of the industrial world and the occurrence of
rapid urbanization processes have led to increase in pollution and en-
vironmental damage. One of the causes of this damage is the disposal
of industrial waste into environment, where one of the materials con-
tained in this waste is a heavy metal which often contaminates our
food through the food chain system. One example of heavy metals is
lead metal or Pb.1
This metal is very toxic so that it can bring serious
problems to the environment and even disrupt human health in trace
amounts exposure. Pb metal is difficult to decompose, so it is difficult
to be eliminated. The accumulation of the Pb metal in the blood can
cause problems with several important human organs such as liver,
kidney, bone, causing damage to the nervous system.2
As much as 1 mg/L of Pb metal in the blood can cause poisoning
in children, so WHO recommends a maximum of 10 μg/L in drink-
ing water. Therefore, this matter has become a serious concern to be
continuously monitored for its existence in nature. Thus, the risk of
exposure to Pb metal in humans can be minimized.2,3
Some instru-
mentation that is commonly used to analyze Pb metal content in the
environment are ICP-MS, HPLC, AAS and also UV-Vis.4–8
However,
because the instrumentation has a large size, so it feels less effective if
it is used to analyze Pb by in-situ or directly in the field. Meanwhile,
under certain conditions, information is needed from the field quickly,
so that the risk of Pb metal pollution in the environment can be known
early and suppressed as low as possible. To overcome the weaknesses
of the existing instrumentation, several sensors have been developed
by previous researchers such as optical sensors, QCM, impedance
and lead underpotential deposition.1,2,8,9
However, these sensors have
disadvantages such as complicated sensor preparation, long response
time and are influenced by the color and turbidity of the sample.
The potentiometric measurements using ion-selective electrodes
(ISE) can be used as a promising alternative in the measurement of
Pb2+
ions in samples. The measurement concept of this potentiometric
sensor is to measure the difference in potential energy that occurs be-
tween ISE and the reference electrode in a state zero current, where the
difference in the potential energy produced will be linearly correlated
with the logarithm of the target ion ions in the sample by following
the phenomenon of the Nernst equation.10–12
The ISE used generally
has a membrane or thin layer that is sensitive to the presence of spe-
cific target ion concentrations.13
The membrane polymer layer is one
of the important components in making this type of the ISE sensor.
This membrane functions as a supporting matrix for the seating of
z
E-mail: sagir.alva@mercubuana.ac.id
other components such as an ionophore and a lipophilic salt.14
The
measurement with this technique provides several advantages com-
pared to other methods, including undamaged samples, undisturbed
by color, wide range measurement, inexpensive, can be run in-situ,
no large numbers of samples are needed and the sensor size can be
reduced.15–17
Since the early 1970s, the research group chaired by Eissesmen has
developed ISE with polymer-based or thin films.18
Polyvinyl chloride
(PVC) membrane is the most widely used membrane.13
However, this
membrane has some fundamental disadvantages such as complicated
preparation, requires a long time and its ability to adhere quite badly to
the surface of the ISE, so the sensor often leaks.19
Examples of ISE for
Pb metal ions that have been developed are like the study of Wilson
et al. in 2010. The Pb sensor developed by Wilson et al. uses 1,3-
bis (N-benzoylthioureido) benzene and 1,3-bis (N-furoylthioureido)
benzene which immobilized on a PVC membrane.20
There are weaknesses that are shown from Pb2+
-ISE as from pre-
vious studies, so there is a need for other alternative membranes. One
material that looks promising is the tetrahydrofurfurylacrylate poly-
mer membrane (pTHFA). This membrane is a membrane of the acrylic
group and has a furan ring and has a Tg value of around −12.2°C21
and
this Tg value is within the area of the Tg value commonly used in ISE
sensor applications which is −20°C–15°C.22–24
In general, this mem-
brane has a tendency to be hydrophilic, so that the process of transport-
ing ions from the sample to the membrane can run well. Other existing
properties that are an advantage of this membrane are that it has good
adhesion properties on the surface of the electrode and can be provided
with a simple technique that is the photo-polymer technique.11,21,25,26
This research aims to develop a Pb2+
-ISE sensor using pTHFA mem-
branes free plasticizer with photo-polymer technique.
Methodology
Instrumentations.—Some of the devices used in this study in-
cludes CS350 electrochemical setup, calomel electrodes (SCE), and
platinum electrodes from Wuhan Corr Test Instrument Corp. Ltd.,
screen-printed electrode (SPE) from Sprint Print Bhd, UV-Box expo-
sure of Huanyu Instrument and 9V batteries.
Materials.—The materials used in this study include the
monomer of a Tetrahydrofurfuryl acrylate (THFA), 2-Hydroxyethyl
methacrylate (HEMA) and 1,6-Hexanediol diacrylate (HDDA) from
Merck. The 2,2-Dimethoxy-2-phenylacetophenone (DMPP), Potas-
sium tetrakis(4-chlorophenyl)borate (KTpClPB), and also Lead
) unless CC License in place (see abstract).
ecsdl.org/site/terms_use
address. Redistribution subject to ECS terms of use (see
129.215.17.190
Downloaded on 2019-11-16 to IP

B1514 Journal of The Electrochemical Society, 166 (15) B1513-B1519 (2019)
Ionophore (IV) from Sigma-Aldrich. The salts such as Pb(NO3)2, KCl,
NaCl, and NH4Cl from Across, while the salts such as MgCl2
.
6H2O,
and CuCl2·2H2O obtain from Merck. The Cd(NO3)2.4H2O get from
Sigma-Aldrich.
Experimental
Ag/AgCl preparation.—The first step of this research is to prepare
Ag/AgCl electrodes through an electrochemical process. The Ag elec-
trodes on SPE and Pt electrodes are connected to 9V batteries, where
Ag acts as a positive pole (+) and Pt electrode acts as a negative pole
(−). The process of AgCl formation on the surface of Ag electrodes
was carried out for 30 seconds in a 0.5 M KCl solution, where the
color of the Ag electrode surface changed from silver to a grayish
color. After the Ag/AgCl layer is formed, the electrodes rinse with
deionized water and dried with a tissue paper. Furthermore, Ag/AgCl
electrodes are stored in a dark place before being used for the next
process.
pHEMA layer.—The pHEMA layer acts as an inner layer and
serves to stabilize the overload on the sensor. The pHEMA layer is
coated on the surface of Ag/AgCl by photo-polymer technique. A
total of 1 ml of HEMA monomer was mixed with 1 mg of DMPP and
1μL of HDDA against HEMA monomers. Subsequently, as much as
0.1μLofthemixturewasdroppedonthesurfaceofAg/AgCl.Thenthe
photo-polymer process is carried out with UV light for 90 seconds in a
UV box in a nitrogen gas flow environment. After the photo-polymer
process is complete, a thin transparent film is formed on the surface
of the polymer. Then the hydration process is carried out by dropping
with a 0.01 M Pb(NO3)2 solution for 15 minutes. After the hydration
process is complete, the electrodes are then ready to be coated with
pTHFA.
THFA layer (sensing membrane layer).—Previously, 1 ml of
THFA monomer was mixed with 1 μl HDDA which functioned as a
cross-linker agent. Furthermore, as much as 100 μL of THFA/HDDA
mixture was added with variations in the concentration of KTpClPB,
Lead (IV) Ionophore, and 1 mg DMMP as a photo-initiator. Further-
more, as much as 3 μL of the mixture was dropped on the surface of the
pHEMA and a photo-polymer process was carried out for 3.5 minutes
in a UV box in an inert gas stream. After the photo-polymer process is
complete a transparent pHEMA layer will be formed on the pHEMA
surface. After that, the electrodes were conditioned in Pb (NO3)2
0.01 M solution for 30 minutes and ready for characterization testing
and validation testing with real and artificial samples. Characterization
testing is done by connecting the Pb2+
sensor as a working electrode
and the calomel electrode as a reference electrode to the potentiometer
equipment and the potential value is measured. The test solution used
was 0.1–10−8
M of Pb(NO3)2. While the validation testing is carried
out using AAS following the SNI 06–6989.8-2004 standard method.
Results and Discussion
Liphophilic salts optimizations.—The function of adding a
lipophilic salt is to manipulate the charge on the membrane used,
the pTHFA membrane. This causes the membrane to have the charge
needed to help facilitate the interaction between the membrane sur-
face and the target ion, which in this case is the Pb2+
ion.17
The
lipophilic salt added to this pTHFA membrane is Potassium Tetrakis
(4-chlorophenyl) borate or KTpClPB as Figure 1 below.
The negative charge on KTpClPB has made the membrane rich in
negative footprint inside the membrane, so that positive ions such as
Pb2+
ions can be attracted into the membrane while negative ions like
nitrate (NO3
−
) will be rejected by the membrane.10
This ion movement
is a coulomb force interaction which states that similar charges will
repel each other while different types of charges will attract each other.
The illustration of ion transfer can be seen in Figure 2.
In this study, the KTpClPB lipophilic salt optimization process was
carried out using three variations of weight, 0.8–1.2 mg, wherein the
Figure 1. Structure of Potassium Tetrakis (4-chlorophenyl)borate KTpClPB.
electrodes provided were tested for their response to the presence of
Pb2+
ions with concentrations of 0.1–10−8
M. The test results can be
seen in Figure 3 and Table I below.
Based on Figure 3 and Table I above, the best sensor composi-
tion is demonstrated by E2 electrode with KTpClPB 1.0 mg lipophilic
salt, whereas the slope of 26.5 mV/dec is closed to the theoretical
Nernstian number for two charged ions of Pb2+
which is 29.6 ±
5 mV/dec.27,28
Whereas 0.8 mg KTpClPB resulted in a low slope
value of 16.6 mV/dec which is below the Nernstian number. While
electrode contained of 1.2 mg KTpClPB showed a super-nernstian
behavior with slope of 48.4 mV/dec.
Electrode with 0.8 mg KTpClPB exhibited a slightly lower slope
value is due to the small number of negative active sites forming on the
pTHFA membrane layer thus limiting the ability of positive charges
Pb2+
ions to enter the polymer membrane matrix. This is also sup-
ported by the fact that the value of the potential difference produced is
lower than electrodes contained 1.0 mg and 1.2 mg KTpClPB lipohilic
salt. Meanwhile 1.2 mg KTpClPB contained salt made the pTHFA
membrane became rich in negatively charged sites so that the Pb2+
ions easily to enter the membrane layer.
This can be seen from the greater amout of lipophilic salt more
than 1 mg KTpClPB produced a super Nernstian potential difference
sensor slope with a value of 48.4 mV/dec. The excessive amount of
KTpClPB causing the membrane to become more polar. Typically a
high polarity sensing matrix is incapable to retain its sensing compo-
nents whereas some components are removed during measurement.
The consequences of high polarity membrane matrix is shown by
E3 sensor performance whereby sensor with 1.2 mg KTpClPb has
the shortest sensor detection range compared to others E1 and E2.29,30
Besides that, Figure 3 also shows the potential value at a concen-
tration of 0.1 M is lower than the 0.01 M concentration. This is at-
tributed by the Donnan effect, whereby Pb2+
ions move onto pTHFA
membrane.31,32
Ionophore optimizations.—In producing ISE, ionophore plays an
important role. In the presence of the ionophore, will cause the mem-
brane to be selective to the targeted ion.17,33
In this research, lead
(IV) ionophore immobilised in pTHFA based polymeric sensing mem-
brane is being study. Limit number of research works using lead (IV)
ionophore have been reported previously.34,35
Optimization is been
Figure 2. The mechanism of ion withdrawal by KTpClPB salts.
129.215.17.190

100
150
200
250
300
350
-9 -8 -7 -6 -5 -4 -3 -2 -1
0.8 mg 1 mg 1.2 mg
Log[Pb2+]
emf
(mV)
vs
SCE
Figure 3. The response of electrodes with variations in the concentration of
KTpClPB in the variation of the concentration of Pb2+ v’s SCE solution.
conducted since a novel polymeric sensing is embedded in sensing
membrane. In general an ionophore has a lipophilic property. The ad-
dition of an ionophore in the sensing membrane will cause a change in
membrane property.33
In this study, the mole ratiometric of lead (IV)
ionophore and 1.0 mg KTpClPB lipophilic salt were carried out with
five variations.
The response of the Pb2+
-ISE sensors with various mole ratio is
shown in Figure 4 and Table II as seen above. The slope of the fabri-
cated sensors increases with with decreasing of lead (IV) ionophore.
As the KTpClPB:Ionophore mole ratio increases to 2:1, the sensor
slope further increases up to 28.6 mV/deC closed to a theoretical value
for a doubly charged ions. It is remarkable seen that the optimum KT-
pClPB: Ionophore mole ratio composition is at a mole ratio of 1:1 with
satisfactory slope value of 28.2 mV/dec and wide linear range from
0.1 M to 10−5
M. The other three KTpClPB:Ionophore mole ratio com-
positions of 1:2, 1:3 and 1:4 shows poor sensor response as compared
to 1:1 ratio. Those compositions contains high amount of ionophores
which has attracted a large amount of Pb2+
ions permeate onto the
sensing membrane while the negative ion, NO3
−
becomes very low.
This has an impact on the ion equilibrium system in the membrane
which becomes unstable and tends to move back toward the aqueous
phase of the sample following the Le Chartlier equilibrium principle.
This equilibrium process will follow the following Equations 1 and 2,
where Kex is a constant equilibrium of Pb(NO3)2.31
Pb2+
(aq) + NO3− (aq)
↔ Pb2+
(membrane) + NO3− (membrane) [1]
Kex =
aPb2+ mem , aNO− mem
3
aPb2+water , aNO−
3 water
[2]
This situation has made the resulting slope under Nernstian num-
bers and the linear range region occurs in areas of low concentration.
In addition, this also causes the potential value generated to also be
greater. Meanwhile, at a ratio of 2:1 mole ratio, the resulting slope
value also closely with the ideal Nernstian number. However, the re-
sulting linear range is shorter and forms following a response pattern
on membranes that only contain mineral salt as shown in Figure 5.
This situation is caused by the number of moles of KTpClPB used
Table I. The electrode performance with variations in the
concentration of KTpClPB in the variation of the concentration
of Pb2+ v’s SCE solution.
E KTpClPB (mg) Slope (mV/dec) LR (M) r2 LOD (M)
E1 0.8 16.6 0.01–10−5 0.9921 4.37 × 10−6
E2 1.0 26.5 0.01–10−5 0.9951 4.57 × 10−6
E3 1.2 48.4 0.01–10−4 0.9995 2.88 × 10−5
100
150
200
250
300
350
400
450
-9 -8 -7 -6 -5 -4 -3 -2 -1
mole rao (1:4) mole rao (1:3) mole rao (1:2)
mole rao (1:1) mole rao (2:1)
Log [Pb2+]
emf
(mV)
vs
SCE
Figure 4. The response of Pb2+-ISE sensor with mole ratio variation
of the KTpClPB: Ionophore in the variation of the concentration of
Pb(NO3)2 solution.
more than the number of moles of the ionophore, so the response of
the Pb2+
-ISE sensor obtained is still quite strong derived from the
KTpClPB salt used.31
Performance lead (II) ion-selective electrode.—In this study, sen-
sor performance is characterised by fabricating three electrodes of
Pb2+
-ISE comprising 1:1 KTpClPB:Ionophore optimum mole ratio
were tested. The tests were immersed in various concentration of
Pb(NO3)2 solution ranging from 0.1 to 10−8
M. Sensor performance
test includes determining Nernstian numbers, linear range limit of de-
tection (LOD), lifetime and also stability. The LOD is the point of
intersection between the linear range region and the region of con-
stant potential change outside the linear range region.36,37
Based on
Figure 6, it appears that at the lower the Pb2+
ions concentration, the
potential emf value decreases due to the number of Pb2+
ions entering
the pTHFA membrane also decreases respectively.
The decrease in potential value due to a decrease in the concentra-
tion of Pb2+
ions is in accordance with the following Nernst equation:
E = Eo
+
RT
zPb2+ F
ln
aPb2+ water
aPb2+ membrane
[3]
E = Eo
+
RT
zPb2+ F
ln aPb2+ water +
RT
zPb2+ F
ln
1
aPb2+ membrane
[4]
At the beginning of the test, the activity of Pb2+
ions in the membrane
was very low which was only dependent on the pHEMA membrane
conditioning process which functioned as an internal solution.17
Based
on the Le Chartlier equilibrium principle that equilibrium will move
from high ion activity to low ion activity, where the activity of the Pb2+
ion in the aqueous phase is higher than the activity of the Pb2+
ion in the
pTHFA membrane. This situation forces the Pb2+
ion in the aqueous
phase to move in such a way as to the pTHFA membrane so that an
Table II. The performance of Pb2+-ISE with mole ratio variation
of the KTpClPB:Ionophore in the variation of the concentration of
Pb(NO3)2 solution.
mole ratio Slope Linear Range
(KTpClPB:Ionophore) (mV/dec) (M) r2
1:4 19.3 10−3–10−6 0.9815
1:3 17.5 10−3–10−6 0.9981
1:2 22.8 10−3–10−5 0.9793
1:1 28.2 0.1–10−5 0.9922
2:1 28.6 10−2–10−5 0.9983
129.215.17.190

125
150
175
200
225
250
275
-9 -8 -7 -6 -5 -4 -3 -2 -1
1 mg KTpClPB mole rao 2:1
Log[Pb2+]
emf
(mV)
vs
SCE
Figure 5. Comparison of Pb2+-ISE sensor response between the use of 1 mg
KTpClPB and 2: 1 mole ratio in various concentrations of Pb(NO3)2 solution.
equilibrium point is reached which is marked by a stable potential
reading. If it is assumed that the ratio of the activity of Pb2+
ions
enteringthemembraneisconstantforeachdifferenceinconcentration,
then the Equation 4 will greatly depend on the concentration of Pb2+
ions in the water, so the Equation 4 can be simplified into Equation 5
below:31
E = Eo
+
RT
zPb2+ F
ln aPb2+ water [5]
Mathematically, the Equation 5 can also be converted into logarithmic
form to:
E = Eo
+
2.303RT
zPb2+ F
log aPb2+ water [6]
Where R is a universal gas constant of 8.314 J/K mol, T is the
temperature in K, F is the Faraday number 96.485 C/mol and z is the
target ion charge.10
If the test is carried out at 25°C, Equation 6 above
will change to:
E = Eo
+ 29.6 mV log aPb2+ water [7]
Furthermore, Figure 6 also shows that at low concentrations of
10−5
M Pb2+
ions, the potential value produced tends to be constant.
This is influenced by the concentration of Pb2 +
ions in the ace phase
is very low, so that its presence in the pTHFA membrane phase is
not strong enough to provide a stimulus for potential changes in the
surface of Ag/AgCl electrodes used in this study.17,38,39
Besides that, in
Figure 6 it can be seen that there is a difference in the potential value for
each Pb2+
ion sensor and this also affects the non-uniform Nernstian
number as shown in Table III, 26.5–29.8 mV/dec. This difference is
based on several factors including:
125
150
175
200
225
250
275
300
325
350
-9 -8 -7 -6 -5 -4 -3 -2 -1
ISE 1 ISE 2 ISE 3
Log[Pb2+]
emf
(mV)
vs
SCE
Figure 6. The responses of the Pb2+-ISE sensor in various concerntration of
the Pb(NO3)2 solutions.
Table III. The performace Pb2+ -ISE in the various concentration
of the Pb(NO3)2 solution.
Slope Linear Range Limit of Detection
ISE (mV/dec) (M) r2 (× 10−6 M)
ISE 1 28.5 0.1–10−5 0.9852 3.80
ISE 2 29.8 0.1–10−5 0.9972 3.24
ISE 3 26.5 0.1–10−5 0.9811 3.98
i. Over time, the formation of Ag2O and Ag2CO3 layers results in
the trapping of O2 and CO2 dissolved in the aqueous phase and
enter the membrane phase, where Ag2O and Ag2CO3 are insula-
tors and will inhibit the charge transfer process on the electrode
surface. The process of formation of Ag2O and Ag2CO3 layers
occurs following the reaction:40
AgCl(s) → Ag(s) + Cl−
(aq) [8]
4Ag(s) + O2 → 2Ag2O(s) [9]
H2O + CO2 → H2CO3(aq) [10]
2Ag(s) + H2CO3(aq) → Ag2CO3(s) [11]
ii. In some studies, the solution of the ionic activity of the internal
solution will affect the LOD region as well as the potential at the
surface boundary of the Ag/AgCl electrode. This is because the
presence of internal solutions will affect the ionic thermodynamic
equilibrium system in the membrane phase.38,39
In this study, the
hydration process was carried out manually with a dripping sys-
tem for 15 minutes on the surface of the pHEMA membrane. The
manual process gives an unequal amount of Pb(NO3)2 that enters
the membrane.
Point (i) also contributes to the lifetime of the Pb2+
ion sensor as
shown in Figure 7 below, where the Pb2+
ion sensor can only be used
for six times.
This can be seen from Figure 7, that on the seventh and eighth
use, the Nernstian number of the Pb2+
ion sensor is already below
25 mV/dec which means it is below the standard Nernstian number
for two charged ions.27,28
In addition, repeated use also causes the
components present in the pTHFA membrane to be released gradually,
where this phenomenon also contributes to the decrease of the Pb2+
ion sensor response.41
In this study, the stability testing of the Pb2+
ion sensor is carried
out by measuring the difference in the potential value of the Pb2+
ion
sensor v’S SCE by using a standard solution of 0.1 M and 0.001 M
solution of Pb(NO3)2. The duration of measurement of 200 minutes,
where the test results can be seen in Figure 8 below. This stability
parameter is one of the important parameters that need to be known
especially for continuous measurement. By testing this stability pa-
rameter, it will be easier to predict when it needs to be recalibrated
0
5
10
15
20
25
30
35
1 2 3 4 5 6 7 8
28.8 30.8
27.5
27.2 26.1 25.5
22.4
19.2
number of use
Nernsan
Value
(mV/dec)
Figure 7. The Nernstian numbers of Pb2+-ISE with eight uses.
129.215.17.190

225
250
275
300
325
350
0 20 40 60 80 100 120 140 160 180 200 220
0.1 M 0.001 M
emf
(mV)
vs
SCE
T (min)
Figure 8. The response of the Pb2+ -ISE sensor in 0.1 and 0.001 M solution
of Pb(NO3)2 for 200 minutes of measurement.
or correct the measurement potential value. Thus, the data generated
becomes more precise and accurate.
Based on Figure 8 above, it can be seen that the response of the Pb2+
ion sensor is quite stable over a measurement period of 200 minutes. At
a concentration of 0.1 M, the range of potential values obtained is be-
tween 326.4–334.6 mV which means the drift occurs is 0.041 mV/min,
while at a concentration of 0.001 M, the potential value generated is
at 271.9–281.7 mV which means the resulting drift is 0.049 mV/min.
This shows that the Pb2+
ion sensor is quite stable and comparable to
previous research reports.42
This is also in accordance with the criteria
set by the International Union of Pure and Applied Chemistry (IUPAC)
regarding the stability of ISE type sensors, where the potential change
that occurs during the measurement is 1 mV/min.43
Coefficent selectivity.—Sensor selectivity test is on of the impor-
tant parameter to be done in the development of ion-selective electrode
(ISE) types such as Pb2+
-ISE. Selectivity test describes the ability of
sensor to respond to the target analyte without influence of presence of
contaminant ions.16,17
This test aims to assess the Pb2+
-ISE sensor’s
performance against target ions even in the presence of an intefering
ion. In this study, the selectivity coefficient test is carried out using the
separated solution method (SSM) at concentration of 0.1M, where the
measurement results are calculated following Equation 12.10,44
The
results of the selectivity coefficient test can be seen in Table IV, where
the interference ions used K+
, Na+
, NH4
+
, Mg2+
, Cu2+
and Cd2+
.
LogKpot
A,B =
(EB − EA) zAF
2.303RT
+

1 −
zA
zB

logaA [12]
Based on Table IV, it shows that the Pb2+
-ISE sensor developed
using pTHFA material has good selectivity for some ionic interfer-
ences. This is consistent with the statement stated by Tang et al. 2018
that the ionophore of the amide group has good effects on the presence
of interference ions as used in this study.39
The resulting decision is
not much different from previous research.45–47
pHeffects.—ThepHeffectisasignificantindexforanewsynthesis
sensing materal in sensor development. Basically the formation of
Table IV. The coefficients selectivity (Log Kpot
a,b) of the Pb2+-ISE
sensor toward various of the interfering ions (n = 3).
Interfering Ion Log Kpot
a,b
K+ −6.5 ± 0.3
Na+ −6.2 ± 0.1
NH4
+ −6.7 ± 0.1
Mg2+ −12.7 ± 0.2
Cu2+ −4.2 ± 0.5
Cd2+ −6.1 ± 0.2
175
190
205
220
235
250
1 2 3 4 5 6 7 8 9 10 11
0.1 M 0.001 M
pH
emf
(mV)
vs
SCE
Figure 9. The response of the Pb2+-ISE in the different pH at 0.1 and 0.001 M
of Pb(NO3)2 solutions.
heavy metal ions such as Pb2+
in aquatic sample depends on the pH
level. Tests were carried out from pH 2 to 10 in 0.1 M and 0.001 M
Pb(NO3)2 solutions. Figure 9 represents the change of the potential
sensor response, emf at different pH level. It is observed that the sensor
response is stable at pH 3–8. This is because, at pH below 3, the lead
(IV) ionophore is deprotonated so it disrupt ionophore functions to
interact with Pb2+
ions.46
Meanwhile, at pH above 8, the state of the
sample solution is in a fairly alkaline atmosphere, where at basic pH
the Pb2+
ion tends to precipitate.48,49
Pb2+
(aq) + OH−
(aq) → Pb(OH)2(s) [13]
In a potentiometry technique requires measurement of the targeted
analyte in the form of ions. Hence if the target material is present
in other forms, it will disrupt the measurement process and provide
inaccurate measurement results.10–13,15,16
Validation test.—The developed sensing material were further
evaluated using two types of solutions, a known artificial solution
concentration and real samples. The aim of this test is to determine
the accuracy of the Pb2+
-ISE sensor to detect Pb2+
ions comparable
to a standard methods. Atomic Absorption Spectrophotometry (AAS)
standard method is been used to validate all the samples. Artificial
solutions used in the study were 10, 50 and 100 ppm, while for real
sample solutions used samples originating from soils at fueling sta-
tions and from river water. The results of validity testing with artificial
samples can be seen in Table V and Figure 10. From the measurement
results between the Pb2+
-ISE and AAS follow the linear regression
equation y = 0.9886x + 0.181 with a value of r2
that is closely 1. This
means that the measurement of artificial samples with Pb2+
-ISE and
AAS basically has identical values, and does not differ greatly from
the concentration of the solution made.
Meanwhile, as explained earlier the real samples is collected from
river water and soil nearby the fueling station. River water samples
were taken from the Cisadane river flow with the coordinates of the
Table V. The comparison of measurements of artificial solutions of
Pb2+ 10, 50 and 100 ppm. ions between Pb2+-ISE and AAS (n =
3).
Pb2+-ISE vs AAS
Pb2+-ISE AAS
[Pb2+] (ppm) ppm Deviation (%) ppm Deviation (%)
10 9.5 ± 0.3 5 10.1 ± 0.4 1
50 52.5 ± 1.7 5 51.1 ± 1.3 2.2
100 100.8 ± 2.5 0.8 100.3 ± 2.2 0.3
129.215.17.190

y = 0.9886x + 0.181
R² = 0.9997
0
20
40
60
80
100
120
0 20 40 60 80 100 120
Lead (II)-ISE (ppm)
AAS
(ppm)
Figure 10. The comparison graph of measurements of artificial solutions of
Pb2+ 10, 50 and 100 ppm ions between Pb2+-ISE and AAS.
South Latitude 6.178400 and East Longitude 106.628278. Cisadane
river flow is one of the rivers in Indonesia, which along with the flow
there has been an extreme process of urbanization, industrialization
and agricultural land clearing and this has become a source of pollu-
tants along with the Cisadane river flow.50
Meanwhile, soil samples from refueling station areas is based on a
large number of fuels in developing countries containing lead metals.
This situation has made the dust and soil around the refueling sta-
tion is contaminated with lead metals. In addition, it was found that
some workers at the fueling station were exposed to the lead.51–53
The
fuel station soil samples used in this study were taken from refueling
stations in the Teluk Naga-Tanggerang-Indonesia area. In this study,
the sample used will be spiking using a standard solution containing
Pb2+
50 ppm ion solution for river water and 10 ppm for soil samples.
This spiking treatment is needed to anticipate the possibility of Pb2+
concentrations in samples that are below the measurement range using
either sensors or AAS. With this spiking treatment, the measurement
results will be more accurate. The results of measurement of the Pb2+
concentration in both samples can be seen in Table VI below.
From the results of measurements made using Pb2+
-ISE and AAS
in the two samples show no significant different. In addition, the mea-
surement results obtained in the Cisadane River are very low and far
below the LOD of Pb2+
-ISE. The value is also still below the Pb2+
ion
concentration value in surface water of 7.2 μg/L according to the rec-
ommendations given by the European Water Framework Directive.35
Meanwhile, in the measurement of concentration in the refueling sta-
tion area, Pb2+
measurements were produced which were not much
different between Pb2+
-ISE and AAS. However, it can be seen from
Table VI that both measurements produce a fairly large standard de-
viation decision, close to the average value of the measurement. This
shows that the distribution of Pb2+
ions in the soil around the fueling
station area is uneven. Pb2+
ion concentration values in this study were
in the range of 1.46–34.94 mg/Kg of soil samples used. The concen-
tration obtained is almost the same as the value of previous studies
conducted in Ghana with a value of 4.93–74.20 mg/Kg.53
Conclusions
Pb2+
-ISE based on the pTHFA photopolymer membrane has been
successfully developed and has demonstrated good selectivity for the
Table VI. Pb2+ -ISE v’s AAS validation testing uses real samples
(n = 3).
Sample Pb2+-ISE AAS
Cisadane River (ppm) 0.0025 ± 0.45 0.0023 ± 0.03
Fuel Station (mg/Kg soil) 18.15 ± 16.74 18.96 ± 15.96
presence of several ions. However, the resulting linear range is not
wide enough which causes the measurement of real samples in the
environment needed to undergo spiking treatment process in order to
get an accurate sample measurement. The sensor response given by
measurements with Pb2+
-ISE is also influenced by the pH of the sam-
ple used. The developed Pb2+
-ISE has shown an excellence accuracy
in determining the concentrations of various samples and comparable
to SNI 06–6989.8-2004 AAS standard method.
Acknowledgments
Thank you to the Universitas Mercu Buana for funding the re-
search through an internal research scheme number 02–5/00438/B-
SPK/III/2019. In addition, a thank you was also conveyed to LIPI-
FISIKA for helping with the validation process of this research. A final
acknowledgment was given to Mimos Berhad, Malaysia who provided
assistance with the materials needed to support this research.
ORCID
Sagir Alva https://orcid.org/0000-0003-3043-7177
Deni Shidqi Khaerudini https://orcid.org/0000-0001-7171-8966
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