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Review

Electrochemical Analysis of Heavy Metal Ions Using Conducting Polymer Interfaces

by
Gerardo Salinas
1,* and
Bernardo A. Frontana-Uribe
2,3,*
1
Groupe NanoSystèmes Analytiques, Ecole Nationale Supérieure de Chimie, de Biologie et de Physique (ENSCBP), University Bordeaux, 33607 Bordeaux, France
2
Departamento de Química Orgánica, Centro Conjunto de Investigación en Química Sustentable UAEM-UNAM, Km 14.5 Carretera Toluca-Atlacomulco, Toluca 50200, Mexico
3
Departamento de Química Orgánica, Instituto de Química, Universidad Nacional Autónoma de México, Ciudad Universitaria, Ciudad de México 04510, Mexico
*
Authors to whom correspondence should be addressed.
Electrochem 2022, 3(3), 492-506; https://doi.org/10.3390/electrochem3030034
Submission received: 10 July 2022 / Revised: 15 August 2022 / Accepted: 19 August 2022 / Published: 26 August 2022
(This article belongs to the Special Issue Surface Modification by Conductive Materials)
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Abstract

:
Conducting polymers (CPs) are highly conjugated organic macromolecules, where the electrical charge is transported in intra- and inter-chain pathways. Polyacetylene, polythiophene and its derivatives, polypyrrole and its derivatives, and polyaniline are among the best-known examples. These compounds have been used as electrode modifiers to gain sensitivity and selectivity in a large variety of analytical applications. This review, after a brief introduction to the electrochemistry of CPs, summarizes the application of CPs’ electrode interfaces towards heavy metals’ detection using potentiometry, pulse anodic stripping voltammetry, and alternative non-classical electrochemical methods.

1. Introduction

Heavy metals are naturally occurring in the earth’s crust; however, anthropogenic and industrial activities have led to drastic change in the metal ions’ nature concentration, provoking pollution in water and soils [1]. Accumulation of toxic metals or an inadequate balance of the required metals in a diet can cause diseases in the human body such as modifications to blood pressure, triglycerides, central nervous system, bones, liver, and kidneys [2,3,4]. Thus, the efficient detection and quantification of heavy metal ions, using selective and sensitive methods, is still needed. Commonly, quantification of heavy metal ions is carried out by atomic absorption spectrometry and inductively coupled plasma optical mass spectrometry [5,6]. An interesting alternative is the use of electrochemical methods, since these present different advantages in comparison with conventional spectroscopic techniques, such as low-cost, fast response times, and straightforward manipulation. In recent years, the use of chemically modified electrodes with conducting polymers (CP) has gained considerable attention [7,8]. This is due to the relative large range of potential where these materials are electroactive, enabling their possible use as conventional electrodes. In addition, the possible surface enrichment, caused by physico-chemical interactions between the metallic ion and the electron-rich atoms within the monomeric structure [9,10,11,12], and the intrinsic porosity of these materials lead to an improvement in sensitivity compared to classic electrodes.
CP are macromolecules with highly conjugated sequences along their oligomeric chain. In these compounds, the electrical charge is transported intra- and inter-chain via generated charge carriers (e.g., σ-dimers, π-dimers, polaron pair, and bipolaron) and it is important not to confuse them with polymeric electrolytes, in which charge is transported by solvated ions [13]. Among the most known and used CPs one can find polyacetylene, polythiophene and its derivatives, polypyrrole and its derivatives, or polyaniline (Figure 1). Such materials have gained considerable attention due to their increasing number of applications: from sensing, to energy storage and conversion, environmental remediation, and bioelectronics [14,15,16,17]. For the past 20 years, different modified electrodes with CPs have been used for the detection of heavy metal ions by using several electrochemical methods, such as potentiometry [18,19,20,21], cyclic voltammetry [22], chronoamperometry [23], and pulse anodic stripping voltammetry [24,25,26,27,28]. Thus, in this review, we discuss the basic concepts involved in the electrochemistry of conducting polymers and summarized the recent efforts concerning the use of modified electrodes with CPs for the possible detection and quantification of heavy metal ions in solution. In addition, this report specially focuses on the different electrochemical methods used for detection and quantification of heavy metal ions.

2. Electrochemistry of Conducting Polymers

As mentioned above, CPs are highly conjugated macromolecules whose electrical, chemical, mechanical, and optical properties can be fine-tuned via the control of the redox state of the polymer. Commonly, the oxidation or reduction of these materials is associated with an uptake or release of ions in order to keep electroneutrality; such a phenomenon is better known as doping. The efficient control of this process, since the properties of these materials are strongly related to the degree of doping, is highly desired. In this frame, electrochemical doping presents different advantages in comparison with chemical doping, where the degree of oxidation is limited by the redox potential of the oxidant or reductant agent. The first advantage is the efficient control of the doping process during the electrochemical polymerization. The most accepted mechanism of electropolymerization is based on a dimerization pathway. Briefly, during the oxidation of the monomer radical cations dimerize at the α-position to form charged σ-dimers, which after proton elimination produce the neutral dimers. Afterwards, such dimer oxidized at lower potentials than the monomer, due to the increase in conjugation, producing a dimer radical cation, which undergoes a series of coupling steps. Once enough oligomeric structures are formed near the electrode, nucleation and growth of short-chain polymeric structures, followed by longer chains formation catalyzed by solid-state redox processes, take place (Figure 2a). Thus, by controlling the applied potential or current, during the electropolymerization, it is possible to fine-tune the physico-chemical properties of the films. For example, high electrode potential values produce cross-linked films with relative low conductivity, whereas low applied potentials lead to smooth and well-ordered polymeric layers.
The second advantage of electrochemical doping is the efficient control of the electrochemical, mechanical, and optical properties of the polymer during the charging/discharging processes. The main characteristic of CPs is the possibility of charging and discharging the polymeric matrix. During the charging of the film, charge carriers are formed, which follows an inter- and intra-chain charge transport mechanism. Such internal charge mobility enables the conductivity of the film. Thus, the efficient control of the injected or extracted charges allows the fine-tuning of the conductivity of the material. In addition, as mentioned above, such insulating/conducting transition is associated with an uptake/release of ions, which is commonly associated with a swelling/compacting process of the film. This leads to the possible electrochemical control of mechanical transitions. Finally, due to their highly conjugated structure, the charging/discharging process of π-conjugated polymers is associated to optical transitions. Commonly, absorption bands of the CP neutral state are found in the visible region while charged states are optically active in the NIR portion of the spectrum. Different physico-chemical models have been proposed to explain the electrical, mechanical, and optical properties of CPs, such as the mixed valence model [29], the bipolaron model [12], the electrochemically stimulated conformational relaxation model [30,31,32], and the memory effect and charge trapping [33,34,35,36]. For more details about the electropolymerization process and the different models, the reader can consult the reviews and book in this field [12,13,37,38,39]. From a technical point of view, different electrochemical methods have been developed for the characterization of π-conjugated polymers, from classic potentiodynamic and potentiostatic techniques to in-situ spectroelectrochemical and conductance methods (Figure 2b–d) [37,40,41].

3. Potentiometry

Potentiometric methods are based on the continuous measurement of the difference of potential (ΔE) between two electrodes, a reference electrode and an ion-selective electrode (ISE), under open circuit conditions [42,43,44]. Commonly, an ISE is constituted by a conductive support in contact with a transducing material and an ion-selective membrane (ionophore). In such configurations, CPs can be used as direct ion-selective membranes. This is due to the possible interaction between the electron-rich atoms within the polymeric matrix and the metallic cations, which changes the interfacial potential of the electrode. For example, pyrene-substituted poly-dithienylpyrrole has been used for the quantification of Fe3+ in aqueous and biological samples, with a limit of detection (LOD) of 9.7 ppb [45]. In another example, nanocomposites of PANI-Sn(II)SiO3 functionalized with carbon nanotubes, for the efficient detection of Hg2+ with a LOD of 0.2 ppb in aqueous solution have been designed [46]. In addition, selectivity and sensitivity of these surfaces can be improved by incorporating selective doping agents inside the polymeric matrix, such as sulphonate anions modified with complexing agents or carmoisine dye complex [47,48]. For example, Ppy doped with tartazine or 5-sulfosalicylic acid for the potentiometric analysis of Zn2+ and Cu2+ with LODs of 0.52 ppm and 0.34 ppm, respectively, has been designed [49,50]. Another alternative is to incorporate into the polymeric backbone an ion-complexing moiety in order to improve selectivity and sensitivity. In this frame, microparticles of a co-polymer formed between m-phenylenediamine and p-sulfonic-m-phenylenediamine substituted with ligand groups (–NH–, –N=, –NH2, and –SO3H) were successfully designed for the analysis of Pb2+ in tap, river water, and human urine with a LOD of 2.6 ppb [51]. Singh et al. developed a chitin-grafted PANI electrode for the quantification of Cu2+, obtaining a LOD of 13.77 ppm, without interferences of different ions [52]. An interesting approach is the use of the so-called ion transfer voltammetry (Figure 3) [53]. In this case, the observed currents correspond to the cation exchange in the polymer matrix and the difference in thermodynamic peak potential was used as the transduction response for the quantification of Li+, Na+, and Ca2+.
An interesting alternative is the use of CP films as the transducing material between the electrode and the ionophore [54,55]. In this case, the ISE electrode can be used in different recognition modes, where instead of measuring the ΔE between the ISE and the reference, the current is evaluated. This is known as the amperometric (coulometric) method, where an amplification of the analytical signal can be obtained by keeping the ΔE constant and measuring the current between the ISE and the reference electrode [56]. Such current causes an oxidation/reduction of the solid transductor, which continues until its ΔE exactly compensates the initial ΔE at the ion-selective membrane/solution interface. Integration of the current transient gives the charge that is proportional to the ΔE at the ion-selective membrane/solution interface originated from the change in activity of metallic ion in solution. For example, the coulometric response of a glassy carbon-PEDOT:poly(sodium styrene sulfonate)-poly(vinyl chloride) electrode (GCE-PEDOT:PSS-PVC) for the detection of Ca2+ and Pb2+ in the mM range was evaluated [57]. This study shows the linear proportionality between the accumulated charge and the logarithm of the activity of the heavy metal ion in solution. Another interesting recognition mode is the accumulation/stripping mechanism presented by Amemiya et al. and extended by Crespo et al. [58,59,60,61]. Briefly, at first during the accumulation step, two fundamental processes occur: the reduction of the CP solid transductor with the concomitant anion release and the cation uptake by the ionophore membrane (Figure 4a). Afterwards, an anodic linear sweep potential is applied, leading to the oxidation of the CP with the correspondent uptake of anions, and the stripping (release) of cations to the solution (Figure 4a). The cation exchange is manifested in a gaussian-shaped voltammetric wave, where changes in the peak potential, current or charge may be used as the analytical signal. The voltammetric response of GCE-poly(3-octylthiophene)-poly(vinyl chloride) for the analysis of Ca2+ showed a characteristic stripping peak in the mM range [53]. On the same principle, a GCE-poly(3-octylthiophene)-silver ionophore IV membrane was used for the detection of Ag+ in the nM range (Figure 4b) [60,61]. In both works, a monovalent cation is used as internal reference, which improves the quantification of Ca and Ag since it minimizes the interferences due to solution matrix.

4. Pulse Anodic Stripping Voltammetry

Pulse voltammetry methods take advantage of the synergy between a double step potential, with a constant pulse time, superimposed to a staircase sweep potential. From the produced pulse wave form, different perturbation diagrams can be designed either by changing the amplitude between the pulses, the frequency of the pulse wave, and the step potential. In addition, these methods can be coupled with a pre-concentration step in order to enrich the electrode surface with the analyte of interest, followed by a pulse anodic stripping voltammetry (ASV) [62]. Among the different pulse anodic stripping voltammetry methods, differential and square wave pulse voltammetry are the most used. The main advantage of these methods is the excellent limit of detection (LOD) that can be reached (in the ppb range) thanks to efficient removal of the capacitive current, since the current is sampled at the end of the pulse potential, where the faradaic current is predominant [63]. Furthermore, these methods present short times of analysis, multi-element detection, possibility of in-flow analysis, and the efficient speciation of analytes with similar thermodynamic redox potential.
In a differential pulse anodic stripping voltammetry (DPASV), the staircase sweep potential is superimposed to both step potential pulses, causing a continuous increase in the base potential. By sampling the forward (if) and backward (ib) current, the plot of the difference of current (if − ib) as function of the applied potential can be obtained. The synergy between chemically modified electrodes with CPs and DPASV has been demonstrated by the quantification of different heavy metal ions, such as Hg2+, Pb2+, Cu2+, Cd2+, and Ni2+ in the ppb range [64,65,66,67,68,69,70,71,72]. However, the current research is focused on increasing the conductivity of the materials, via formation of composites, and the incorporation of complexing agents into the polymeric matrix. For example, composites formed by carbon materials such as graphene, graphene oxide, and single-walled carbon nanotubes, and PANI have been used for the detection and quantification of Hg2+, Pb2+, Cu2+, and Cd2+ in the ppb range [73,74,75,76,77]. Carbon materials increase the electroactive area and the conductivity of the composite, which translate to an enhancement of the sensitivity of the electrodes [78,79]. Incorporation of complexing agents into the polymeric matrix can be achieved either by the fine-tuning of the monomer structure or by using complexing agents such as doping counterions [80,81,82]. Recently, Pudel, et al. developed a pencil graphite electrode modified by poly(pyrrole-1-carboxylic acid) (Ppy-CO2@PGE) for the sensitive quantification of Pb2+ and Cd2+ by DPASV [83]. The porous structure of the film uniformly distributes carboxylate groups throughout the complete modified electrode in order to selectively coordinate and pre-concentrate metal ions inside the polymer matrix. The obtained DPASV show a simultaneous linear relationship between the peak current and the metal ion concentration with LODs of 0.018 and 0.023 nM for Pb2+ and Cd2+, respectively (Figure 5a,b). An interesting approach is the use of self-doped CPs as sensitive electrodes for the quantification of heavy metal ions. For example, self-doped PANI film was prepared by copolymerization of polyaniline and metanilic acid (anionic doping agent) for the possible quantification of Bi3+ ions [84]. The obtained DPASV show a linear relationship between the stripping current and the metal ion concentration in the nM-mM range with a LOD of 0.48 nM. In this work, the complexing mechanism is based on the uptake of Bi3+ ions during the discharge of the PANI backbone in order to keep electroneutrality, followed by the correspondent reduction of the metal ion.
Square wave anodic stripping voltammetry (SWASV) follows the same principle as DPASV, where the staircase sweep potential is superimposed to both step potential pulses, with the difference that in this method the amplitude between the pulses (ESW) increases up to 50 mV. With a similar philosophy, by sampling if and ib, the plot of the difference of current (if − ib) as function of the applied potential can be obtained. SWV is characterized by four parameters: the square wave period, the pulse time (tp), the step potential (ΔEs), and ESW. The pulse time is related to the square wave frequency f = (1/2tp) and since the sweep potential is constant, the scan rate is defined by v = ∆ES/2tp = f∆ES. In addition to the efficient removal of the capacitive current, SWV minimize problems related to adsorption of organic molecules at the electrode surface. SWASV has been successfully coupled with chemically modified electrodes with CPs for the quantification of different heavy metal ions, such as Hg2+, Pb2+, Cu2+, Cd2+, and Ni2+ in the ppb range [85,86,87,88,89]. For example, a platinum electrode modified with PEDOT and Nα,Nα-bis-(carboxymethyl)-L-lysine hydrate (NTA lysine) (PEDOT/NTA) was used for the quantification of Hg2+, Pb2+, and Zn2+ ions in water by using SWASV. Linear responses to the three different ions in the concentration range of 5–100 μg L−1 were obtained, with LODs of 1.73, 2.33, and 1.99 μg L−1, for Hg2+, Pb2+, and Zn2+, respectively [90]. Enhancement of the conductivity of the electrode material, via incorporation of graphene, has been reported using SWASV for the quantification of different heavy metal ions in the ppb range [91,92]. Another alternative to enhancing conductivity is the use of gold nanoparticles [93]. Lu et al. reported the synthesis of polyaniline coated with gold nanoparticles (Au@PANI) for the simultaneous quantification of Pb2+ and Cu2+ using SWASV [93]. The electrode shows excellent electrochemical response during the simultaneous analysis of Pb2+ and Cu2+ with a LOD of 3 and 8 nM, respectively. The presence of the gold nanoparticles significantly increases the conductivity of the CP and enhances the adsorption capability of the material. Finally, an interesting alternative for enhancing the electroactive area is the use of highly ordered macroporous electrodes. In general, the formation of ordered porous structures within CP enhances the ion transport inside the polymer matrix and increases the contact surface. Highly ordered macroporous electrodes made out of poly-3,4-ortho-xylendioxythiophene (PXDOT), by using the Langmuir-Blodgett (LB) technique, were designed for the efficient quantification of Cu2+ [94]. LB technique is based on the formation of colloidal crystal templates of silica beads on the electrode surface. Afterwards, the macroporous electrodes are obtained by the correspondent electrodeposit of the CP, followed by the removal of the template. By this procedure, ordered structures with interconnected pores and uniform thickness can be obtained. In this work, the surface of the electrodes presents gaps between the hexagonal structures formed by the pores of the PXDOT film (Figure 5c). This is caused by an interaction between the radical cation, formed during the electropolymerization, and the surface groups of the silica beads, which leads to a surface-templating mechanism. The SWASV analysis of Cu2+ with such ordered structures shows a linear response in the sub-ppm range. In addition, the efficient quantification of Cu2+ in commercial mezcal samples was achieved (Figure 5d).

5. Alternative Non-Classical Electrochemical Methods

Conventional electrochemical methods are based on either a potential sweep or pulse. Although such methods enable the possible quantification of heavy metal ions, their LODs are relatively lower than the ones obtained by potentiometry of pulse anodic stripping voltammetry. However, there are a few examples that are well worth mentioning, in particular due to the particular design of the CP used for the quantification. For example, crown-annelated terthiophenes containing 3,4-ethylenedioxythiophene were designed for the possible potentiodynamic detection of Pb2+ [95]. The monomer presents a shift of oxidation potential of 200 mV and a relative linear increase in the peak current as function of the concentration of Pb2+. This was attributed to the complexing ability of the monomer toward Pb2+ ions. Amperometric monitoring of Fe3+ was carried out using a GCE modified with an Ppy/poly(4-(2,3-dihydrothieno [3,4-b][1,4]dioxin-2-yl-methoxy)-1-butanesulfonic acid hydrogel [96]. The modified electrode shows a reduction current proportional to the Fe3+ ion concentration in the micromolar range, with a LOD of 0.8 µM. Sannegowda et al. designed a cobalt(II) tetraamide benzimidazole phthalocyanine (CoTABImPc)-conducting polymer for the analysis of Hg2+ at the nanomolar range by using cyclic voltammetry, differential pulse voltammetry, and chronoamperometry [97]. The amperometric method showed an excellent sensitivity in the nanomolar range with a LOD of 3 nM, in comparison with CV and DPV (Figure 6a).
Finally, since conductivity is a bulk transport property, relative small perturbations on the mobility of the counterions or the charge carrier’s results in larger variations of conductivity in comparison to changes in potential or current. Thus, the in situ electrochemical-conductance method can be used as a powerful technique for the possible quantification of heavy metal ions in solution. This is based on an interdigitated microelectrode arrangement (IDME), where the conductance of the deposited films between the branches is calculated directly from Ohm’s law. For a deeper insight into the details of this technique, we invite the readers to consult a recent published review [37]. Although this method has been used particularity for the study of the conductivity profile of CPs in the presence of monovalent cations [98,99], the influence of different heavy metal ions on the electric properties of this materials has been evaluated. For example, calix [4]arene-bithiophene presents a selective conductivity response to K+, Ba2+, and Ca2+ (Figure 6b) [100]. A considerable decrease in the conductivity of these polymers in the presence of Ba2+ was observed. This has been attributed to perturbations in the charge-hopping conductivity due to the charge balancing between the redox segments and the metal ions. Swager’s group reported an enhancement of the conductivity of polymetallorotaxanes and three-strand conducting ladder polymetallorotaxanes in the presence of copper [101,102]. In these polymers, the electroactivity of the copper ions assist the interchain transport, which causes an improvement in conductivity. However, these studies are focused on the design of on-off recognition systems, leaving the analytical applications of these method for future works.

6. Conclusions

Modified electrodes with CPs are a clear option for gaining sensitivity and selectivity for heavy metals detection and analysis. The different matrix where they have been used and the conducting polymer structures available opens a myriad of possibilities for the fine-tuning of the metal analysis. Lower cost of analysis compared with classical techniques (Atomic absorption or Plasma spectroscopy), excellent limits of detection (Table 1), possibility of multi-element analysis, and speciation in a single experiment, as well as in-flow analysis, are the major advantages for exploring selective electrodes modified with CPs. The reviewed examples showed that the field is in expansion and that, in the future, commercial application of these metal sensitive electrodes could be developed using low-cost screen-printed electrode, available with different companies. However, the design of simpler and faster electrochemical transduction methods is still a challenge. Due to the outstanding electrochemical, mechanical, and optical properties of conducting polymers, we envisage the development of novel in situ and wireless electrochemical methods for the possible metallic ion analysis in real samples.

Author Contributions

G.S.; writing—original draft preparation, review, and editing, B.A.F.-U.; writing—review and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by PAPIIT-DGAPA UNAM, through the project IN208919 and AV200222.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

We thank the technical support of Lic. Citlalit Martínez. The support of CONACYT, through the projects AV200222 and A1-S-18230 are recognized.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Chemical structures of the most known families of conducting polymers.
Figure 1. Chemical structures of the most known families of conducting polymers.
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Figure 2. Schematic illustration of the (a) long chain propagation catalyzed by solid-state redox processes and different electrochemical and spectroelectrochemical responses obtained during the electrochemical characterization of CP; the possible physico-chemical response obtained during (b) potentiodynamic and conductance measurements, (c) potentiostatic and gravimetric analysis, and (d) spectroelectrochemical experiments.
Figure 2. Schematic illustration of the (a) long chain propagation catalyzed by solid-state redox processes and different electrochemical and spectroelectrochemical responses obtained during the electrochemical characterization of CP; the possible physico-chemical response obtained during (b) potentiodynamic and conductance measurements, (c) potentiostatic and gravimetric analysis, and (d) spectroelectrochemical experiments.
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Figure 3. (a) Proposed response mechanism of a cation exchanger (R−)-based thin layer membrane backside contacted with POT during the forward scan and backward scan. (b) Top: Cyclic voltammograms for the cation exchanger-based membrane MII in contact with 10 mM NaCl at a scan rate of 100 mV s−1. Bottom: Calculated cyclic voltammograms at three concentration levels of NaCl (scan rate 100 mV s−1); inset, Epeak vs. log aNa+. Adapted from reference [53].
Figure 3. (a) Proposed response mechanism of a cation exchanger (R−)-based thin layer membrane backside contacted with POT during the forward scan and backward scan. (b) Top: Cyclic voltammograms for the cation exchanger-based membrane MII in contact with 10 mM NaCl at a scan rate of 100 mV s−1. Bottom: Calculated cyclic voltammograms at three concentration levels of NaCl (scan rate 100 mV s−1); inset, Epeak vs. log aNa+. Adapted from reference [53].
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Figure 4. (a) Schematic illustration of the accumulation of ions in the ionic-selective membrane (m) and the corresponding stripping towards the solution (s) with a representation of the associated chemical reactions, and the potentiostatic accumulation response and the anodic stripping voltammogram. (b) Linear sweep voltammograms obtained during the stripping of Ag+ at increasing concentrations (indicated on the figure) in 10 mM NaNO3 background solution (top), and plot of the peak current for the peaks corresponding to the Na+ and Ag+ transfers versus the Ag+ concentration (bottom). Adapted from reference [60].
Figure 4. (a) Schematic illustration of the accumulation of ions in the ionic-selective membrane (m) and the corresponding stripping towards the solution (s) with a representation of the associated chemical reactions, and the potentiostatic accumulation response and the anodic stripping voltammogram. (b) Linear sweep voltammograms obtained during the stripping of Ag+ at increasing concentrations (indicated on the figure) in 10 mM NaNO3 background solution (top), and plot of the peak current for the peaks corresponding to the Na+ and Ag+ transfers versus the Ag+ concentration (bottom). Adapted from reference [60].
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Figure 5. (a) DPASV voltammograms for the simultaneous analysis of Pb2+ and Cd2+ at the Ppy-CO2@PGE. (b) Calibration plots of Pb2+ (blue circles) and Cd2+ (red squares). Adapted from reference [83]. (c) SEM images of a cross-section of a highly ordered macroporous PXDOT electrode. Insets show a close-up of the gaps (red) and the interconnection points (blue). (d) SWASV for successive addition of Cu2+ obtained with a macroporous PXDOT electrode in a 10% diluted mezcal solution. Inset shows a plot of peak current vs concentration of added copper. Adapted from reference [94].
Figure 5. (a) DPASV voltammograms for the simultaneous analysis of Pb2+ and Cd2+ at the Ppy-CO2@PGE. (b) Calibration plots of Pb2+ (blue circles) and Cd2+ (red squares). Adapted from reference [83]. (c) SEM images of a cross-section of a highly ordered macroporous PXDOT electrode. Insets show a close-up of the gaps (red) and the interconnection points (blue). (d) SWASV for successive addition of Cu2+ obtained with a macroporous PXDOT electrode in a 10% diluted mezcal solution. Inset shows a plot of peak current vs concentration of added copper. Adapted from reference [94].
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Figure 6. (a) Amperometric curve for different Hg2+ concentrations at a GCE/poly(CoTABImPc) in a 0.1 M PBS pH 7.0, applied potential 0.18 V. Inset: Plot for current response as function of the Hg2+ concentration. Adapted from reference [97]. (b) In-situ conductivity measurements for poly-calix [4] arene-bithiophene films with K+, Ba2+, and Ca2+ ions in a 5 μm interdigitated microelectrode at a v = 5 mV/s with a ΔV in the WE = 40 mV. Adapted from reference [100].
Figure 6. (a) Amperometric curve for different Hg2+ concentrations at a GCE/poly(CoTABImPc) in a 0.1 M PBS pH 7.0, applied potential 0.18 V. Inset: Plot for current response as function of the Hg2+ concentration. Adapted from reference [97]. (b) In-situ conductivity measurements for poly-calix [4] arene-bithiophene films with K+, Ba2+, and Ca2+ ions in a 5 μm interdigitated microelectrode at a v = 5 mV/s with a ΔV in the WE = 40 mV. Adapted from reference [100].
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Table
Table 1. Metallic cations analyzed using conducting polymers modified electrodes.
Table 1. Metallic cations analyzed using conducting polymers modified electrodes.
Electrochemical MethodConducting PolymerCationLODRef
PotentiometryPANIHg2+0.2 ppb[46]
Cu2+0.128 ppm[47]
Cu2+13.77 ppm[52]
Cu2+0.64 ppb[21]
PpyZn2+0.52 ppm[49]
Cu2+0.34 ppm[50]
Poly-Dithienyl pyrroleFe3+9.7 ppb[45]
PEDOTAg+ND[19]
Ca2+ND[57]
Pb2+ND
Polycarbzole (PCbz)Cu2+0.65 ppm[20]
Co-Polysulfonic phenylenediaminePb2+0.026 ppm[51]
POTCa2+0.84 ppm[53]
Ca2+0.012 ppb[60,61]
Differential Pulse Anodic Stripping VoltammetryPANIHg2+56.37 ppb[64]
Pb2+0.21 ppb[65]
Pb2+20 ppb[67]
Pb2+0.83 ppb[68]
Cu2+0.38 ppb
Pb2+
Cu2+		0.01 ppb[69]
0.04 ppb
Hg2+7.6–0.03 ppm[70]
Cd2+0.16–0.03 ppm
Pb2+13–0.04 ppm
Ni2+0.06–0.02 ppm
Pb2+0.033 ppb[71]
Cd2+0.029 ppb
Cu2+1.27 ppm[72]
Pb2+0.1 ppb[73]
Hg2+0.44 ppm[74]
Cd2+0.15 ppm
Pb2+2.03 ppm
Hg2+0.612 ppb[75]
Cu2+0.088 ppm[76]
Pb2+0.34 ppm[77]
Hg2+0.13 ppm
Ni2+0.058 ppm[78]
Cd2+0.3 ppb[82]
Bi3+0.48 nM[84]
PpyPb2+1.98 ppb[66]
Pb2+0.07 µM[79]
Pb2+0.014 ppm[83]
Cd2+0.023 nM
PThAg+60 ppb[27]
Cu2+ND[28]
Hg2+ND
Pb2+20.7 ppb[80]
PEDOTZn2+2 ppm[26]
Cd2+0.6 ppm
Pb2+0.5 ppm
Cu2+0.6 ppm
As3+0.5 ppm
Poly(2-amino terephthalic acid)Hg2+0.49 ppb[81]
Cd2+0.13 ppb
Pb2+0.16 ppb
Zn2+0.089 ppb
Square Wave Anodic Stripping VoltammetryPANIPb2+ND[85]
Pb2+0.05 ppb[86]
Cd2+0.04 ppb
Pb2+0.069 ppb[87]
Pb2+0.267 ppb[88]
Cu2+0.283 ppb
Cd2+0.097 ppb
Cd2+50 ppb[89]
Cu2+0.063 nM[92]
Pb2+0.045 nM
Cd2+0.03 nM
Pb2+0.62 ppb[93]
Cu2+0.51 ppb
PpyCu2+0.32 ppb[25]
Pb2+0.1 ppb
Cd2+5.6 ppb
Hg2+40 ppb
PThPb2+0.12 ppb[24]
Cu2+0.013 ppb
Hg2+0.1 ppb
PEDOTPb2+2.33 μg L−1[90]
Hg2+1.73 μg L−1
Zn2+1.99 μg L−1
Poly-terthiopheneZn2+0.05 ppb[91]
Cd2+0.08 ppb
Pb2+0.2 ppb
Cu2+0.09 ppb
Hg2+0.1 ppb
PXDOTCu2+ND[94]
Cyclic VoltammetryPpyCu2+ND[22]
Pb2+ND
Cd2+ND
Zn2+ND
PTh-PEDOTPb2+ND[95]
ChronoamperometryPEDOTPb2+0.04 ppb[23]
Ppy, PEDOTFe2+0.8 µM[96]
Poly-phthalocyanineHg2+3.8 nM[97]
In situ Electrochemical-ConductancePBThBa2+ND[100]
Ca2+ND
PTh-PEDOTCu2+ND[101,102]
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Salinas, G.; Frontana-Uribe, B.A. Electrochemical Analysis of Heavy Metal Ions Using Conducting Polymer Interfaces. Electrochem 2022, 3, 492-506. https://doi.org/10.3390/electrochem3030034

AMA Style

Salinas G, Frontana-Uribe BA. Electrochemical Analysis of Heavy Metal Ions Using Conducting Polymer Interfaces. Electrochem. 2022; 3(3):492-506. https://doi.org/10.3390/electrochem3030034

Chicago/Turabian Style

Salinas, Gerardo, and Bernardo A. Frontana-Uribe. 2022. "Electrochemical Analysis of Heavy Metal Ions Using Conducting Polymer Interfaces" Electrochem 3, no. 3: 492-506. https://doi.org/10.3390/electrochem3030034

APA Style

Salinas, G., & Frontana-Uribe, B. A. (2022). Electrochemical Analysis of Heavy Metal Ions Using Conducting Polymer Interfaces. Electrochem, 3(3), 492-506. https://doi.org/10.3390/electrochem3030034

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