Universidad Nacional de Chimborazo

NOVASINERGIA 2019, Vol. 2, No. 2, Diciembre (75-83)

ISSN: 2631-2654

https://doi.org/10.37135/unach.ns.001.04.08

Research Article

http://novasinergia.unach.edu.ec

Detection of Cd (II) and Pb (II) by anodic stripping voltammetry using

glassy carbon electrodes modified with Ag-Hg and Ag-Bi bimetallic alloyed

Detección de Cd (II) y Pb (II) por voltamperometría de separación anódica

utilizando electrodos de carbono vidriosos modificados con aleación bimetálica Ag-

Hg y Ag-Bi

Danny Valera

, Mireya Sánchez

, José Domínguez

, Patricio J. Espinoza-Montero

, Carlos

Velasco-Medina

, Patricio Carrera

, Lenys Fernández

1,2*

Departamento de Química, Universidad Simón Bolívar, Caracas, Venezuela, 89000; dannyvalera@usb.ve

Escuela de Ciencias Químicas, Pontificia Universidad Católica del Ecuador, Quito, Ecuador, 170525; mires-

40@hotmail.com; patoespinozamon@hotmail.com

Facultad de Ingeniería Química, Escuela Politécnica Nacional, Quito, Ecuador, 170525; carlos.velasco@epn.edu.ec

Hidroecuador, Quito, Ecuador, 170801; info@nanoinstrumentos.net

* Correspondence: lmfernandez@puce.edu.ec

Recibido 10 noviembre 2019; Aceptado 06 diciembre 2019; Publicado 10 diciembre 2019

Abstract:

We report the evaluation of glassy carbon (G.C.) electrodes modified with Nafion

(Nf) films and bimetallic alloyed Ag-Hg and Ag-Bi deposits. Most of the

deposited bimetallic, with an average size of approximately 150 nm, were

uniformly dispersed and embedded inside the Nafion net cells. In contrast, a much

lesser amount of them remained on top of the embedded ones without any regular

orientation as indicated by scanning electron microscopy (SEM) and atomic force

microscopy (AFM) images. Sensitivity tests for the AgBiNf/G.C. modified

electrode produced detection limits (DL), based on the variability of a blank

solution (3 s criterion), of 0.78 and 0.66 μg L

-1

for Cd(II) and Pb(II), respectively,

whereas for the AgHgNf/G.C. modified electrode D.L.s were 0.17 and 0.24 μg L

for Cd(II) and Pb(II), respectively. Accuracy of the anodic re-dissolution

voltammetry methodology was checked by calculation of percentages of recovery

of the two analytes, expressed as a relative error. Recovery from 99 % to 92 %

was achieved.

Keywords

Bimetallic alloyed, modified electrodes, Pb and Cd anodic stripping voltammetry.

Resumen:

Presentamos la evaluación de los electrodos de carbono vítreo (GC) modificados

con películas de Nafion (Nf) y depósitos bimetálicos de aleaciones Ag-Hg y Ag-

Bi. La mayoría de los bimetálicos depositados, con un tamaño promedio de

aproximadamente 150 nm, se dispersaron e incrustaron uniformemente dentro

de la red del Nafion. En contraste, una cantidad mucho menor permaneció

encima de las incrustadas sin ninguna orientación regular, como lo indica

imágenes de microscopía electrónica de barrido (SEM) y microscopía de fuerza

atómica (AFM). Las pruebas de sensibilidad para el electrodo modificado

AgBiNf/GC produjeron límites de detección (DL), basados en la variabilidad de

una solución en blanco (criterio de 3 s), de 0,78 y 0,66 μg L

-1

para Cd (II) y Pb

(II), respectivamente; mientras que el DL sobre el electrodo modificado

AgHgNf/GC fue 0,17 y 0,24 μg L

-1

para Cd (II) y Pb (II), respectivamente. La

precisión de la metodología por voltametría de redisolución anódica se verificó

mediante el cálculo de porcentajes de recuperación de los dos analitos,

expresados como error relativo. Se logró una recuperación del 99% al 92%.

Palabras clave:

Aleación bimetálica, electrodos modificados, voltamperometría de redisolución

anódica de Pb y Cd.

http://novasinergia.unach.edu.ec 76

1 Introduction

Monitoring heavy metals in the environment and

biological samples are of utmost importance for

evaluating and preserving the environment and public

health quality levels.

One of the best ways of performing this monitoring is

through sensitive and fast response sensors used in

situ. Sensors with these characteristics provide real-

time results useful to establish reference locations

needed to follow the contaminants' behavior as a

function of location and time. This type of study is

increasingly necessary because heavy metals

concentration in the environment keeps growing due

to the larger augment in global anthropogenic

activities. Consequently, more and more heavy metals

get into the environment and, through the food chain,

into the human organism (Karri, Schuhmacher, &

Kumar, 2016). Among the contaminants, Cd(II) and

Pb(II) are the ones that could be most dangerous to

human health (Wan, Kan, Rogel, & Dalida, 2010).

Cadmium could get into the human organism via

inhalation or by food or drink ingestion. It could act as

a cancer promoter by altering the regular genetic

expression, inhibiting DNA reconversion, and

inducing oxidative stress (Singh & Mishra, 2009; Lin,

Zhang, & Lei, 2016). The lead could get into the

human organism similarly, as Cd does. Lead, as a

contaminant, among other effects, could supplant

calcium in proteins causing protein malfunctioning

and thus impairing physiological functions (Zhang et

al., 2015). Since Cd and Pb appear not to have known

natural biological functions, the presence of these

elements in the human body, at any concentration

level, must be due to contamination. Institutions such

as the Center for Disease Control (CDC), International

Agency for Cancer Research (IACR), and World

Health Organization (WHO) have dictated maximum

concentration limits permitted for these metals,

including Cd and Pb, in food, drinks, biological and

environmental samples (Gumpu, Sethuraman,

Krishnan, & Rayappan, 2015). Cd and Pb

concentration levels in non-contaminated geological

and environmental samples are usually relatively low,

10 g L

-1

. However, those low levels must be

accurately known to start a study regarding the extent

of a possible contamination process by these two

elements as a function of time.

Evaluation of electrochemistry-based techniques

together with the best way of preconcentration and

isolation of heavy metals for their accurate

determination has been the goal of several research

studies (Zhu, Zhu, & Wang, 2006; Liang, Li, & Yang,

2005; Abkenar et al.,2010; Abkenar, Dahaghin,

Sadeghi, Hosseini, & Salavati-Niasari, 2011;

Dahaghin, Mousavi, & Sajjadi, 2017a; Dahaghin,

Zavvar, & Sajjadi, 2017b; Bagheri et al., 2012; Huang,

Ding, & Li, 2014; Huang, Rao, Li, & Ding, 2011;

Bhatluri, Manna, Ghoshal, & Saha, 2017). Among the

most widely used electrochemistry techniques for Cd

and Pb determination, based on their high sensitivity

and freedom from matrix effects, anodic re-dissolution

voltammetry (ASV) is one of the most convenient.

During the first step of the ASV methodology, the

analyte's ions in solution are reduced by electrolysis

under reducing potential conditions, by way of which

the analyte is separated from most of the sample's

matrix freeing its measurement from most matrix

effects. The reduced analyte's preconcentration

follows this step by its deposition on the working

sensor's surface, which increases the technique's

detection capacity. Finally, the analyte is re-dissolved

under anodic re-dissolution conditions originating an

electrical signal proportional to the analyte's

concentration.

Fabrication of an electrode, which could function

close to the ideal one for lead and cadmium

determination at trace level in complex matrices, has

been the objective of many research studies (Xiong,

Ye, Hu, & Xie, 2016). In most cases, mercury and

mercury film-based electrodes are selected due to their

excellent re-dissolution capacity (Zhu, Gao, Choi,

Bishop, & Ahn, 2004; Lakshmi, Sharma, & Prasad,

2007; Ferreira & Barros, 2002). However, the

presence of a highly toxic element, as in massive

mercury sensors, makes them inadequate from the

point of view of contamination (Cargnelutti et al.,

2006). To further diminishing toxicity, bismuth, a

more ecologic element, was chosen instead of mercury

as a modifier for the sensor (Pei et al., 2014; Borgo,

Jovanovski, Pihlar, & Hocevar, 2015). Based on those

findings, we have tried several glassy carbon (G.C.)

modified electrodes for the determination of Cd(II)

and Pb(II) in human serum and urine samples (Valera

et al., 2018).

In the present work, we report on the determination of

Cd and Pb in human serum and urine samples using

two electrodes, the first one consisting of a G.C.

electrode covered by a Nafion (Nf) film doped with

HgAg alloyed and the second one by BiAg alloyed.

2 Experimental

2.1 Reagents

Nafion (5% (w/w)) was purchased from Aldrich;

BiNO

.5H

O(98%), cadmium nitrate (99.5%); lead

nitrate (99.5%), and hydrogen peroxide (6% (w/w))

were purchased from Merck; silver nitrate, 99.8%,

nitric acid (65%), acetic acid (99.8%) and ethanol

(99.8%), were purchased from Riedel- de Haën.;

potassium hydroxide (87.8%) was purchased from J.T.

http://novasinergia.unach.edu.ec 77

Baker; sodium hydroxide (98%) was purchased from

Eka Nobel; sodium acetate (98%), and

dimethylformamide (DMF) were purchased from

Sigma. All reagents used were analytical grade

reagents or better unless otherwise stated. Aqueous

solutions were prepared using distilled/deionized,

18M  cm

-1

Millipore water.

2.2 Instrumental

Electrochemical measurements were carried out using

a Princeton Applied Research (PAR), 273A model

Galvanostat/Potenciostat, computer-controlled by the

270/250 Research Electrochemistry Software 4.23

from PAR, coupled to a conventional 15 mL three-

electrode reaction cell. The modified electrodes in the

evaluation were used as working electrodes; Ag/AgCl

electrodes were used as a reference, and 0.5 cm

diameter platinum wires were the counter electrodes.

Scanning electron microscopy (SEM) analyses were

performed using a PHENOM PROX tabletop

scanning electron microscope. A PARK SYSTEMS

equipment (NX10) was used for the ex-situ atomic

force microscopy (AFM) studies.

2.3 Deposition of alloyed bimetallic

deposits

G.C. electrodes were chosen as substrates for the

deposition of the alloyed bimetallic to produce the

modified electrodes. As a previous step, the G.C.

electrodes were firstly polished using the number 2000

sandpaper and afterward using spreads of aluminum

oxide powder, with decreasing particle size 1.0 µm,

0.3 µm, and 0.05 µm, on a billiard tablecloth. After

polishing, the G.C. electrode was submerged in an

ultrasonic bath containing distilled/deionized water

for 5 minutes to eliminate any aluminum oxide

particle loosely adhered to the glassy carbon. Five

microliters of a 1% Nf solution were cast on the G.C.

electrode using a micropipette. Immediately, 3 µL of

pure DMF was added with a micropipette. Ethanol and

DMF used as solvents were evaporated by heating at

C with an air gun and rotating the electrode at 50

rpm.

After this treatment, the electrode, already covered

with an Nf film, was submerged in an aqueous

solution having either 85% Ag and 15% Hg or 85%

Ag and 15% Bi for 3 hours. Afterward, the electrode

was carefully washed with distilled/deionized water to

remove non-absorbed material. Finally, the metallic

ions trapped in the Nf net are reduced by submitting

the electrode to Coulombimetry at controlled potential

(CPC) at -1.2 V for 300 seconds in a 1mol L

-1

KNO

0.1 mol L

-1

HNO

solution.

2.4 Sample recollection and treatment

2.4.1 Blood

A modified method according (Valera et al., 2018).

Professional nurses collected blood samples directly

into new "Vacutainer" tubes containing EDTA as an

anticoagulant. After gentle shaking to promote contact

with de EDTA solution, the samples were refrigerated

until taken for analysis. For analysis, blood samples

were centrifuged at 3000 rpm for 15 minutes to

separate serum from the rest of the sample. Two

milliliters of serum were diluted with 15 mL

distilled/deionized water under gentle shaking and 8

mL conc. Nitric acid was added, and the sample was

left shaking for 5 minutes to initiate digestion. After

this time, 1 mL of a 30 % hydrogen peroxide solution

was added. The samples were ultrasonicated for 30

minutes at 60 °C, then diluted to 25 mL with

distilled/deionized water, which renders them ready

for analysis.

2.4.2 Urine

A modified method according (Valera et al., 2018).

Donors collected urine samples in virgin urine

collection vessels. Donors were informed about the

study and instructed on the best way of avoiding

contamination during collection. Samples were

immediately acidified with 2 mL conc. Nitric acid to

avoid metal hydrolysis and microorganism growth and

refrigerated until taken for digestion. Digestion was

initiated on 10 mL of filtered samples (Whatman N°

1" filter paper) by adding 1 mL conc. Nitric acid plus

1 mL of a 30% hydrogen peroxide solution. Samples

were then left under gentle shaking for 5 minutes and

ultrasonicated for 30 min. at 60°C. Finally, samples

were diluted to 25 mL with distilled/deionized water

rendering them ready for analysis.

2.5 Determination of Cd (II) and Pb (II)

by Anodic Stripping Voltammetry

For the preconcentration step, 15 mL of a 0.1 mol L

-1

pH 4.5, acetate buffer solution, and precisely known

volumes of Cd(II) and Pb(II) standard solutions were

added to a three-electrode conventional cell. The cell

was then purged with an argon flow (20 mL min

-1

) for

5 minutes, and a -1.2 V potential was applied for 120

s, with continuous agitation followed by a 10 s period

with no agitation.

Differential pulse voltammetry (DPV) scanning at 20

mV s

-1

within the range from -650 to -350 mV vs.

Ag/AgCl, was used for the re-dissolution step. After

each concentration/re-dissolution cycle, the

http://novasinergia.unach.edu.ec 78

electrode's Cleaning was achieved by applying a -200

V vs. Ag/AgCl potential for 15 s.

3 Results and Discussion

3.1 Modified electrodes

characterization

Figure 1a shows a micrograph of the Nf film covering

the G.C. electrode (Valera et al., 2018), which is the

first step in preparing the modified Nf/G.C. electrode.

The whole Nf film seems flat in the figure, presenting

some holes, approximately 900 to 950 nm in diameter,

seen as dark spots.

Figure 1b shows a micrograph of the resulting

AgBiNf/G.C. electrode's surface, obtained after 180

min (Valera et al., 2018). Immersion of the Nf covered

the G.C. electrode in a 0.85 µg L

-1

Ag + 0.15 µg L

-1

solution. SEM images allow for the appreciation of

metallic particles, white spots inside the Nf film.

Particles with an approximate particle diameter of 150

nm were obtained.

The images of the surfaces after individual immersion

for 180 minutes of G.C. electrodes in an Ag-Hg

solution to produce the AgHgNf/G.C. electrode are

shown in figure 1c (Valera et al., 2018).

Although the particle size of the AgBi alloys seems to

be smaller (150 nm) than the particle size of the

AgHg (200 nm), the latter shows a more dispersed

distribution. AFM images are shown in figure 2. These

images suggest that the Nf film completely covers the

G.C. electrode (figure 2a). After deposition of the

bimetallic particles, the images suggest that the

particles are three-dimensionally dispersed throughout

the polymer film, figure 2b (Valera et al., 2018).

3.2 Nafion film thickness

The simplest way of covering the G.C. electrode with

an Nf film is by applying a small volume of an Nf

solution to the electrode followed by adding a small

DMF volume to increase the polymeric film's stability

(Kefala, Economou, & Voulgaropoulos, 2004). Nf

film thickness can be controlled by adding to the

glassy carbon substrate a given volume of solutions

containing different Nf concentrations.

We added fixed volumes of solutions containing Nf

concentrations of 1% (w/v). Assuming a uniform

distribution of the Nf solution on the glassy carbon

electrode's surface (as indicated by the SEM images),

film thickness I

can be calculated, to a first

approximation, by the formula I

= m

/ πR

(Valera et al., 2018); where m

is the mass of Nf

deposited on the electrode; d

is the density of the Nf

film (1.58 g cm

-3

), and R is the radius of the glassy

carbon electrode (1.5 mm). With the addition of 5 µL

of solutions containing 1.0 % w/v Nf and a volume of

DMF of 3 µL, films with thickness 4.47 µm were

obtained.

3.3 Preconcentration potential

Starting with 120 s preconcentration time, the

influence of Cd's preconcentration potential and Pb's

re-dissolution were studied in a -0.8 V to -1.3 V

potential range.

The results depicted in figure 3a indicate that current

peaks increase from -0.9 V to -1.2 V, and peaks start

decreasing at -1.2 V. Given these results, -1.2 V was

chosen as the optimal re-dissolution potential for best

preconcentration of Cd and Pb.

3.4 Pre-concentration time

As preconcentration time plays a significant role in

analyte's accumulation, a 1.2 V potential was applied

to a 50 µg L

-1

de Cd(II) and Pb(II) solution to find out

the amount of Cd and Pb accumulated on the

AgHgNf/G.C. and the AgBiNf/G.C. electrodes as a

function of time accumulation were estimated by

measuring the redissolution charge (µC) for each

metal (figure 3b). Increasing time from 0 to 300 s

resulted in augmented re-dissolution currents,

indicating increased amounts of each analyte on the

electrode's surface. After 300 s, the current starts to

stabilize and keeps its value up to 400 s and even

longer times; 120 s was selected as preconcentration

time for all measurements.

3.5 Working range and sensitivity

Figure 4a depicts the working curves for Cd's

simultaneous re-dissolution (blue dots) and Pb (orange

dots), using the AgBiNf/G.C. electrode. Both analytes

behave similarly regarding their current-concentration

linear relationship. The lead response is seen to be

more sensitive. Linearity is kept from around 10 to

120 µg L

-1

, being limited by electrode surface

saturation. After a 120 s preconcentration time,

detection limits calculated based on the 3s criterion

measuring blank solutions were 0.78 µg L

-1

for Cd(II)

and 0.66 µg L

-1

for Pb(II), n = 6. Results obtained

using the AgHgNf/G.C. electrode are shown in figure

4b. This figure was constructed in the same way as

figure 4a using the corresponding current values from

the voltammograms shown in the inset. Both analytes

respond quite differently at this electrode. Sensitivity

for Pb is higher than for Cd; the linear range is the

same for both metals, meaning that the process of

electrode surface saturation is very similar for both

electrodes. After a preconcentration time of 120 s,

detection limits calculated based on the 3 s criterion

http://novasinergia.unach.edu.ec 79

measuring blank solutions were 0.17 µg L

-1

for Cd(II)

and 0.24 µg.L

-1

for Pb(II), n = 6

Figure 1: SEM images of the Nf ﬁlm covering the G.C. electrode and the Nf covered G.C. electrode surface after (a)

60 s. (b) 180 minutes of immersion of the Nf covered G.C. electrode in a 0.85 mg L

-1

Ag + 0.15 mg L

-1

Bi solution

and then reducing the metallic ions trapped in the Nf net by CPC, and (c) After 180 minutes of immersion of the Nf

covered G.C. electrode in a 0.85 mg L

-1

Ag + 0.15 mg L

-1

Hg solution and then reducing the metallic ions trapped in

the Nf net by CPC (Valera et al., 2018)

Figure 2: AFM images: (a) High magniﬁcation images (scan region 5 mm), showing the thickness of the AgBi

nanoparticle. (b) AgBiNpNf on the G.C. substrate; the image shows the three-dimensional arrangement of alloyed

nanoparticles, Ag–Bi (Valera et al., 2018).

http://novasinergia.unach.edu.ec 80

Figure 3: (a) Eﬀect of the analyte preconcentration potential on the charge. (b) Eﬀect of analyte preconcentration time

on determination of 50 mgL

-1

Pb (II).

(a)

(b)

Figure 4: (a) Calibration curves at AgHgNf / CV electrode. (b) Calibration curves at AgBiNf / CV electrode.

http://novasinergia.unach.edu.ec 81

Figure 5: Repeatability study for measurements of Pb(II) and Cd(II) by ASV using the AgBiNf/G.C. and

AgHgNf/G.C. electrodes.

3.6 Precision of measurements

After a 120 s preconcentration time from a 40 µg

-1

Cd and Pb solution, twenty consecutive

determinations of each metal were carried out,

figure 5. Relative standard deviation (RSD) values

range from 1.18 to 4.61. These could be considered

outstanding RSD values attesting to an exact

methodology.

3.7 Determination of Cd and Pb in

human blood serum and urine samples

Modified electrodes were applied to Cd and Pb's

determination in human blood serum and urine

samples collected from donors living in a rural area

that was part of a broader environment pollution

study. Samples were collected from students of the

University (Universidad Simon Bolivar, Caracas-

Venezuela), doped with 40 µg L

-1

of both Cd(II)

and Pb(II), and analyzed following the analytical

protocol described in section 2.5.

The ASV methodology's accuracy was checked by

calculation of percentages of recovery of the two

analytes, expressed as a relative error, R (table 1).

Results in Table 1 demonstrate that Pb's

determination can be achieved, with recoveries

within 96 to 99 % in both types of samples, serum,

and urine, using any new electrodes.

This accuracy indicates that these samples' organic

matrices do not represent a limitation in Pb's

determination. However, this is not the case for the

determination of Cd in blood serum samples for

which R% was 80% using the AgBiNf/G.C.

electrode and even more extensive, 53%, using the

AgHgNf/G.C. electrode.

These results show that AgBi alloyed are more

convenient for modifying Nafion covered G.C.

electrodes destined to analyze organic samples

with complex matrices than the AgHg alloy.

Modifying the Nf/G.C. electrodes with AgHg

alloyed nanoparticles produces electrodes

unsuitable for Cd analysis in blood serum due to

their unacceptable inaccuracy. Nonetheless, for

urine, a sample with a lighter matrix than blood

serum, the AgHgNf/G.C. electrode produces

accurate results with recoveries within 92 to 94%.

Tabla 1: Results

Analyte

AgBiNf/GC

found

(µgL

-1

)

AgHgNf/GC

found

(µg L

-1

)

AgBiNf/GC

found

(µg L

-1

)

AgHgNf/GC

found

(µg L

-1

)

AgBiNf/GC

R (%)

AgHgNf/GC

R (%)

Serum

Urine

Serum

Urine

Serum

Urine

Cd (II)

41.16 ± 4.12

29.35 ± 4.43

46.23 ± 2.77

46.79 ± 2.66

80.32

92.46

52.84

93.59

Pb (II)

48.27 ± 1.94

48.69 ± 1.91

49.01 ± 2.15

49.48 ± 2.92

96.54

98.02

97.37

98.96

http://novasinergia.unach.edu.ec 82

4 Conclusion

Results show that the new electrodes could be

useful for Pb determination in human serum and

urine samples with acceptable accuracy and

precision. The new electrodes' ASV technique

offers a faster, lower cost, more mobile, and easier

to operate alternative. The AgHgNf/G.C. electrode

has the advantage of being slightly more sensitive

than the AgBiNf/G.C. for Cd and Pb

determination. However, it is not useful for Cd

determination in serum samples due to a lack of

accuracy. Even though the AgHgNf/G.C.

electrode still contains mercury, this amount of

mercury is infinitesimally lower than that in a

massive Hg sensor so that the electrode can be

used with practically no harm to people or the

environment.

We believe that improved accuracy and sensitivity

in the bimetallic modified electrodes could be due

to the metallic couple's synergistic effects.

Conflicts of Interest

The authors declare no conﬂict of interest.

Acknowledgment

The authors would like to thank Escuela de

Ciencias Químicas y Dirección de Investigación de

la Pontificia Universidad Católica del Ecuador

(PUCE) and Decanato de Investigación y

Desarrollo de la Universidad Simón Bolívar

(USB), Caracas-Venezuela for financial support.

References

Abkenar, S. D., Hosseini, M., Dahaghin, Z., Salavati-

Niasari, M., & Jamali, M. R. (2010). Speciation

of chromium in water samples with

homogeneous liquid-liquid extraction and

determination by flame atomic absorption

spectrometry. Bulletin of the Korean Chemical

Society, 31(10), 2813-2818.

Abkenar, S. D., Dahaghin, Z., Sadeghi, H. B., Hosseini,

M., & Salavati-Niasari, M. (2011).

Determination of zinc in water samples by flame

atomic absorption spectrometry after

homogeneous liquid-liquid extraction, Journal

of Analytical Chemistry, 66(6), 612-617.

https://doi.org/10.1134/S1061934811060062

Bagheri, A., Behbahani, M., Amini, M. M., Sadeghi, O.,

Tootoonchi, A., & Dahaghin, Z. (2012).

Preconcentration and separation of ultra-trace

palladium ion using pyridinefunctionalized

magnetic nanoparticles, Microchimica Acta,

178(3-4), 261-268.

https://doi.org/10.1007/s00604-012-0815-4

Bhatluri, K. K., Manna, M. S., Ghoshal, A. K., & Saha,

P. (2017). Separation of cadmium and lead from

wastewater using supported liquid membrane

integrated with in-situ electrodeposition,

Electrochimica Acta, 229, 1-7.

https://doi.org/10.1016/j.electacta.2017.01.090

Borgo, S. D., Jovanovski, V., Pihlar, B., & Hocevar, S.

B. (2015). Operation of bismuth film electrode

in more acidic medium, Electrochimica Acta,

155 196-200.

https://doi.org/10.1016/j.electacta.2014.12.086

Cargnelutti, D., Tabaldi, L. A., Spanevello, R. M., de

Oliveira, G., Battisti, V., Redin, M., …

Chitolina, M. R. & Morsch, V. M. (2006).

Mercury toxicity induces oxidative stress in

growing cucumber seedlings. Chemosphere,

65(6), 999-1006.

https://doi.org/10.1016/j.chemosphere.2006.03.

037

Dahaghin, Z., Mousavi, H. Z., & Sajjadi, S. M. (2017a).

Trace amounts of Cd (II), Cu (II) and Pb (II) ions

monitoring using Fe

@graphene oxide

nanocomposite modified via 2-

mercaptobenzothiazole as a novel and efficient

nano sorbent. Journal of Molecular Liquids,

231, 386-395.

https://doi.org/10.1016/j.molliq.2017.02.023

Dahaghin, Z., Zavvar, H., & Sajjadi, S. M. (2017b).

Synthesis and Application of Magnetic

Graphene Oxide Modified with 8‐

Hydroxyquinoline for Extraction and

Preconcentration of Trace Heavy Metal Ions.

Chemistry Select, 2(3), 1282-1289.

https://doi.org/10.1002/slct.201601765

Ferreira, M. A., & Barros, A. A. (2002). Determination

of As(III) and arsenic(V) in natural waters by

cathodic stripping voltammetry at a hanging

mercury drop electrode. Analytical Chimica

Acta, 459(1), 151-159.

https://doi.org/10.1016/S0003-2670(02)00086-

Gumpu, M.B., Sethuraman, S., Krishnan, U. M., &

Rayappan, J.B.B. (2015). A review on detection

of heavy metal ions in water – an

electrochemical approach. Sensors and

Actuators B: Chemical, 213, 515–533.

https://doi.org/10.1016/j.snb.2015.02.122

Huang, M. R., Ding, Y. B., & Li, X. G. (2014).

Combinatorial screening of potentiometric Pb

(II) sensors from polysulfoaminoanthraquinone

http://novasinergia.unach.edu.ec 83

solid ionophore. ACS Combinatorial Science, 16

(3), 128-138.

https://doi.org/10.1021/co400140g

Huang, M. R., Rao, X. W., Li, X. G., & Ding, Y. B.

(2011). Lead ion-selective electrodes based

onpolyphenylenediamine as unique solid

ionophores. Talanta, 85(3), 1575-1584.

https://doi.org/10.1016/j.talanta.2011.06.049

Kefala, G., Economou, A., & Voulgaropoulos, A.

(2004). A study of Nafion-coated bismuth-film

electrodes for the determination of trace metals

by anodic stripping voltammetry. Analyst, 129

1082–1090. https://doi.org/10.1039/B404978K

Karri, V., Schuhmacher, M., & Kumar, V. (2016).

Heavy metals (Pb, Cd, As and MeHg) as risk

factors for cognitive dysfunction: A general

review of metal mixture mechanism in brain.

Environmental Toxicology and Pharmacology,

48, 203-213.

https://doi.org/10.1016/j.etap.2016.09.016

Lakshmi, D., Sharma, P. S., & Prasad, B. B. (2007).

Imprinted polymer-modified hanging mercury

drop electrode for differential pulse cathodic

stripping voltametric analysis of creatine.

Biosensors and Bioelectronics 22(12), 3302-

3308.https://doi.org/10.1016/j.bios.2006.12.011

Liang, P., Li, J., & Yang, X. (2005). Cloud point

extraction preconcentration of trace cadmium as

1-phenyl-3-methyl-4-benzoyl-5-pyrazolone

complex and determination by flame atomic

absorption spectrometry. Microchimica Acta,

152, 47-51. https://doi.org/10.1007/s00604-005-

0415-7

Lin, J., Zhang, F., & Lei, Y. (2016). Dietary intake and

urinary level of cadmium and breast cancer risk:

A meta-analysis. Cancer Epidemiol, 42, 101-

107.

https://doi.org/10.1016/j.canep.2016.04.002

Pei, X., Kang, W., Yue, W., Bange, A., Heineman, W.

R., & Papautsky, I. (2014). Improving

Reproducibility of Lab-on-a-Chip Sensor with

Bismuth Working Electrode for Determining Zn

in Serum by Anodic Stripping Voltammetry.

Journal of the Electrochemical Society, 161(2),

B3160-B3166.

https://doi.org/10.1149/2.022402jes

Singh, D. K. & Mishra, S. (2009). Synthesis,

characterization and removal of Cd (II) using Cd

(II) ion-imprinted polymer. Journal of

Hazardous Materials, 164(2-3), 1547-1551.

https://doi.org/10.1016/j.jhazmat.2008.09.112

Valera, D., Sánchez, M., Domínguez, J. R., Alvarado, J.,

Espinoza-Montero, P. J., Carrera, P., Bonilla, P.,

Manciati, C., González, G. & Fernández, L.

(2018). Electrochemical determination of lead in

human blood serum and urine by anodic

stripping voltammetry using glassy carbon

electrodes covered with Ag–Hg and Ag–Bi

bimetallic nanoparticles. Analytical Methods,

10(34), 4114-412.

https://doi.org/10.1039/C8AY01314D

Wan, M. W., Kan, C. C., Rogel, B. D., & Dalida, M. L.

P. (2010). Adsorption of copper (II) and lead (II)

ions from aqueous solution on chitosan-coated

sand. Carbohydrate Polymers, 80(3), 891-899.

https://doi.org/10.1016/j.carbpol.2009.12.048

Xiong, S., Ye, S., Hu, X., & Xie, F. (2016).

Electrochemical detection of ultra-trace Cu (II)

and interaction mechanism analysis between

amine-groups functionalized CoFe

/reduced

graphene oxide composites and metal ion.

Electrochimica Acta, 217,24-33.

https://doi.org/10.1016/j.electacta.2016.09.060

Zhang, H., Shuang, S., Wang, G., Guo, Y., Tong, X.,

Yang, P., … Qin, Y. (2015). TiO

-graphene

hybrid nanostructures by atomic layer

deposition with enhanced electrochemical

performance for Pb(II) and Cd(II) detection.

RSC Advances, 5, 4343-4349.

https://doi.org/10.1039/C4RA09779C

Zhu, X., Zhu, X., & Wang, B. (2006). Determination of

trace cadmium in water samples by graphite

furnace atomic absorption spectrometry after

cloud point extraction. Microchimica Acta, 154

(1) 95-100. ttps://doi.org/10.1007/s00604-005-

0476-7

Zhu, X. S., Gao, C., Choi, J. W., Bishop, P. L., & Ahn,

C. H. (2004). On-chip generated mercury

microelectrode for heavy metal ion detection.

Lab on a Chip, 5, 212-217.

https://doi.org/10.1039/B410006A