Mercury Drop Research Articles

Free gallium (III) determination with AGNES (Absence of Gradients and Nernstian Equilibrium Stripping)

Gallium is being extensively used in technological applications. Increasing emissions to the environment classify it as an emerging contaminant. Speciation information, such as the free gallium concentration, [Ga3+], is fundamental for understanding/predicting its bioavailability and potential toxicity to biota. In this work, [Ga3+] in aqueous solutions at pH2 and 3 has been measured with AGNES (Absence of Gradients and Nernstian Equilibrium Stripping). The deposition times to reach equilibrium, for a fixed accumulation factor or gain, were longer than those required with other metals such as Zn, Pb, Cd and In. This is attributed to the electrodic irreversibility of the couple Ga0/Ga3+ on the mercury electrode together with low concentrations of relatively poorly labile and/or poorly reversible (for the electrodic transfer) hydroxy complexes. When the AGNES-SCP variant was applied in the Hanging Mercury Drop Electrode with radius 141 μm, and the transition time was ≤10 s, the correction of the deposited mass with a depletion factor was essential. The speciation capacity of AGNES for Ga was evaluated with the phthalate ligand at pH 3 and the experimental results obtained were very similar to the theoretical results predicted with the stability constants in the NIST and Brown-Ekberg databases.

Bismuth Film Electrodes: Characterization and Analytical Application

Bismuth film electrodes (BiFE) were first introduced more than two decades ago and have been regarded as a posible alternative to toxic traditional mercury electrodes, both for electro-synthesis and electro-analytical endeavors. However, despite all the associated benefits, there hasn’t been a proper characterization reported for this electrodes and their use is still limited.The present work shows the results of a physicochemical characterization of Bismuth film electrodes, as well as the application of BiFE for the detection and quantification of heavy metals (such as cadmium), which for years have been considered to be important pollutants and are toxic for humans and the environment at large; there for putting at risk the health of all organisms that come into contact with them. The analysis is carried out in a EtOH:H2O mixture at pH 5, simulating the matrix of a traditional mexican alcoholic beverage, Mezcal.The characterization includes: the calculation of the geometric area as well as the electro-active area of the electrode, the composition of the deposited film and it’s texture, and the electrical properties of the modified electrode.The analysis is carried out using Anodic Stripping Square Wave Voltammetry (ASSWV), this allows us to make use of the electrode’s ability to form strong interactions with the analyte, in a similar manner to that of mercury drop electrodes; along with the high sensitivity of this technique.

Computer Simulation of a Capillary “Jump” of a Mercury Drop or an Air Bubble Under Conditions of Short-Term Weightlessness

The capillary “jump” of drop of mercury or an air bubble that occurs during the transition of gravity acceleration from earth to microgravity is called a drop of mercury sharp “jump” starting from the bottom of a container with water, where it is located, to its top or a sharp “jump” of the surface of the air shell, which has turned into a spherical air bubble, starting from the top of a container with water down to the bottom of the container. Article presents both a computer model of a capillary “jump” of a mercury drop in a container with water and computer model of a capillary “jump” of an air bubble in a container with water, previously developed by author during the transition of gravitational acceleration from earthly to microgravity. The developed computer models, implemented in the Turbo C and Turbo Basic computer languages, permitted to simulate on the computer display a capillary “jump” of mercury drop and an air bubble in container with water; quantitatively to calculate the energy of motion of a capillary “jump” of a mercury drop and an air bubble in container with water during the transition of the acceleration of gravity from earth to microgravity. The results of calculations of the energy of motion of a capillary “jump” of a mercury drop showed that the surface tension of a mercury drop plays a significant role in the driving of a mercury drop compared to its density. Flight tests have shown that the developed computer models can be successfully used in main systems of spacecraft under conditions of microgravity to predict the occurrence of a capillary “jump” of wide range real mercury drops and air bubbles in these systems.

Evaluation of hemilabile Pd(II) NNS and NNSe non-symmetric pincers in Suzuki–Miyaura cross-coupling: Unexpected selective nitrile hydration of 4-bromonitrobenzene in mild conditions

In this work, four non-symmetric NNS and NNSe Pd(II) pincer complexes (1–4) supported by tridentate iminophosphorane ligands bearing both the indole heterocycle and a varying chalcogenoether pending arm [XR = SPh (1), SePh (2), SMe (3), SeMe (4)], were tested in the Suzuki–Miyaura cross coupling reaction between phenyl boronic acid and aryl bromides. The modest catalytic activity of complex 3 under conventional heating (110 °C), was boosted under microwave irradiation, leading to excellent yields of coupling under remarkably mild conditions: 5 min of reaction time at 70 °C under aerobic conditions. The complexes supported by NNS ligands proved to be more robust and superior catalysts than those supported by NNSe ligands, which tended to decompose under catalytic conditions. Among the four complexes, pincer 3 also demonstrated the best catalytic performance and was tested in the coupling of a variety of p-substituted bromobenzenes. Notably, the catalytic performance of complex 3 was unaffected by the mercury drop test, and with most substrates in the series, the percentage of conversion reflected the aryl bromides’ Hammett parameter. However, little to no coupling occurred with p-bromobenzonitrile and the reaction with p-nitrobenzene resulted in only limited conversion yields. In fact, when activated using microwave irradiation, complex 3 unexpectedly catalyzed the nitrile hydration of p-bromobenzonitrile, yielding p-bromobenzamide under remarkably mild Suzuki–Miyaura coupling conditions.

Sensitive and Simple Electroanalytical Method for Lead Detection in Seawater Using VAdS with Eriochrome Blue Black R

A novel electroanalytical approach for lead detection was developed using the voltammetric adsorptive stripping (VAdS) method with Eriochrome Blue Black R (EBBR) as the complexing agent. The method operates by accumulating the Lead-EBBR complex on a hanging mercury drop electrode (HMDE) and measuring the peak current. The complex reduces at -0.46 V, with the peak current increasing as small amounts of EBBR are introduced into the sample. Key parameters such as pH, EBBR concentration, accumulation time (tacc), and accumulation potential (Eacc) were optimized. Under optimal conditions (pH 3, 0.6 mol/L EBBR, tacc 60 s, Eacc 0.35 V, and 40 mmol buffer), the peak current correlated directly with Lead (II) concentrations from 0.05 to 100 µg/L, with a detection limit of 0.01 µg/L. The method exhibited high precision, with a relative standard deviation of 0.5% for a 10 µg/L Lead (II) solution over ten trials. Validation of the method was achieved by comparing results from seawater samples from former bauxite mining areas, using Atomic Absorption Spectrophotometry (AAS), showing similar outcomes. The VAdS method proved highly effective for detecting Lead (II) in seawater contaminated by mining waste.

Ceftazidime Dosage Investigation using Differential Pulse Polarography for Pharmaceuticals

An accurate direct DPP identification of ceftazidime has been made for use in drug discovery and validation. The results showed that a mercury drop of 3 mm3, an acidic medium consisting of a KH phthalate plus HCl buffer solution at pH 2, and 1 ml of NH4Cl, 1 M as a supporting electrolyte were optimal for ceftazidime analysis.Ceftazidime exhibited two peaks, the first at - 0.67V and the second at - 1.06V. For the determination of an unknown concentration, a standard graph of ceftazidime in concentrations ranging from 8.410-6 M to 2.610-5 M was developed. The reliability and accuracy of this technique for analysing the analyte were assessed. For ceftazidime laboratory samples, the SD was 0.1885 and the RSD% did not go above 4.573% at a concentration of 4.6 μg.ml-1, 8.410-6 M, and at a concentration of 8.5 μg.ml-1, 1.510-5 M, the SD was 0.35645 and the RSD% did not go over 4.345%. The peak potential Ep, and the actual number of electrons required for the reduction of ceftazidime are both calculated using the Ilkovic-Heyrovsky equation. The data show that ceftazidime requires five electrons for the reduction reaction to occur. The method has been successfully used to get ceftazidime on the market.Keywords: Ceftazidime, DPP, Analysis.

N-methyl mesoporphyrin IX (NMM) as electrochemical probe for detection of guanine quadruplexes

G-quadruplexes (G4) are stable alternative secondary structures of nucleic acids. With increasing understanding of their roles in biological processes and their application in bio- and nanotechnology, the exploration of novel methods for the analysis of these structures is becoming important. In this work, N-methyl mesoporphyrin IX (NMM) was used as a voltammetric probe for an easy electrochemical detection of G4s. Cyclic voltammetry on a hanging mercury drop electrode (HMDE) was used to detect NMM with a limit of detection (LOD) of 40 nM. Characteristic reduction signal of NMM was found to be substantially higher in the presence of G4 oligodeoxynucleotides (ODNs) than in the presence of single- or double-stranded ODNs and even ODNs susceptible to form G4s but in their unfolded, single-stranded forms. Gradual transition from unstructured single strand to G4, induced by increasing concentrations of the G4 stabilizing K+ ions, was detected by an electrochemical method for the first time. All obtained results were supported by circular dichroism spectroscopy. This work expands on the concept of electrochemical probes utilization in DNA secondary structure recognition and offers a proof of principle that can be potentially employed in the development of novel electroanalytical methods for nucleic acid structure studies.

Adsorption, 2D-condensation, and redox reactions of bile acids on the hanging mercury drop electrode

Bile acids (BAs) are natural surfactants thanks to the facial amphiphilic character of the steroid skeleton. For the first time, the electrochemical and adsorption behaviour of selected bile acids differing in the number of hydroxyl groups on the steroid skeleton – lithocholic acid (3α-OH), deoxycholic acid (3α- and 12α-OH), and cholic acid (3α-, 7α- and 12α-OH) – was investigated on hanging mercury drop electrode (HMDE) in mixed Britton – Robinson buffer: methanol (9:1) media. In cyclic voltammetry, all BAs yielded a negative signal at the potential of ca −1.4 V with intensity depending on pH of the solution. Further, sharp tensammetric signals confirming adsorption/desorption or re-organization processes of the adsorbed molecules were observed. AC voltammetric measurements revealed two-dimensional (2D) condensation of lithocholic acid in the pH range 12.0–7.0 visualized by the formation of a capacitance pit. Adsorption of the other studied BAs was indicated by the AC current density decrease. Measurements of differential capacitance dependences - potential (C-E curves) revealed this behaviour to be concentration and temperature dependent. A study on effect of halides (Cl−, Br−, I−) on the adsorption of bile acids showed involvement of primarily hydrophobic interactions in the BA interaction with the HMDE surface.

Poisonous Truth about the Mercury Drop Test: The Effect of Elemental Mercury on Pd(0) and Pd(II)ArX Intermediates

Poisonous Truth about the Mercury Drop Test: The Effect of Elemental Mercury on Pd(0) and Pd(II)ArX Intermediates

(Invited) Electrochemistry of Exceptionally Inert Systems: Determination and Speciation of Arsenic(III) and Arsenic(V)

There has been growing interest in development of new methods for the determination of arsenic oxo species due to their high toxity and increasing population in the environment. Electrochemical methods for the determination of arsenic can be considered as complimentary to spectroscopic and chromoatographic ones because they are fairly simple, and they are subject to different selectivity criteria. In this respect, various stripping voltammetric procedures are becoming popular. The actual stripping voltammetric measurement consists of two steps in which preconcentration of an analyte at the electrode surface is followed by the so called „stripping” step involving electrode reaction recorded in a form of the voltammetric peak. A representative approach involves reduction of the analyte anions upon application of the sufficiently negative potential to form As(0) on the electrode (e.g. gold) surface; this step is followed by voltammetric oxidation (anodic stripping) of the deposit (to As(III)). In a case of so called cathodic stripping voltammetry, the stationary Hanging Mercury Drop Electrode (HMDE) is often used. During the preconcentration step, an insoluble salt (e.g. Cu3As2) is produced on the electrode surface. There is also a need to differentiate between As(III) and As(V) oxo-species, which are relatively more and less toxic, respectively.Because sensitivity and detection limit in electroanalytical determinations strongly depend on the current densities measured, there is a need to search for specific catalytic materials that would induce otherwise highly slow and irreversible redox processes of As(III) (oxidation) and, in particular, As(V) (reduction). Our research interests concern development of highly specific catalytic systems leading to the enhancement of the electrooxidation of arsenic (III). We explore here the capability of various noble metals nanoparticles (Pt, Rh, Pd) of inducing the arsenic(III) oxidation in acidic medium. The recorded currents have been compared to those observed previously at the electrodes modified with oxocyanoruthenates, the most potent system for the electrocatalytic oxidation of AsIII(OH)3. Reduction of arsenic (V) is even the more inert reaction. Network films of bimetallic (PtRu) nanoparticles (bare and derivatized) permit preconcentration of arsenic(V) species on their surfaces. The stripping step would allow determination of low concentrations of arsenic (10-6 mol/dm-3 or lower).

Adsorption of 4-aminopyrimidine at the R-AgLAFE/chlorate(VII) interface. Comparison of the adsorption properties of various water activity as well as different surfactants

The results of 4-aminopyrimidine (4-APM) impact studies on the double layer parameters at the R-AgLAFE/ chlorates(VII) interface in the solutions with different water activity as well as different properties of the mixed adsorption layer of 4-aminopirimidine – sodium 1-decanesulfonate (SDS) and 4- aminopyrimidine - hexadecyltrimethylammonium bromide (CTAB) at the electrode/solution interface are discussed.The differential capacity of the double layer (Cd) at the R-AgLAFE/ basic solution interface was measured using the electrochemical impedance spectroscopy. The zero charge potential (Ez) was determined using a streaming electrode, while the surface tension at the zero charge potential (Yz) was measured using the largest pressure method inside the mercury drop. It was proved that both the 4-aminopirymidine concentration and water activity have an essential effect on the doublelayer parameters on the R-AgLAFE/ chlorates(VII) interface. In the studied systems: 4-APM - SDS and 4-APM - CTAB, 4-aminopyrimidine dominance was observed.

Fast and reliable voltammetric determination of menaquinone (vitamin K2) produced in vitro by Bacillus subtilis cultures

Vitamin K2 (VK2) is one of two natural forms of vitamin K, necessary for the proper functioning of organisms. Currently, it is sourced from chemical synthesis, nonetheless, it is worth reaching out to its natural sources. The aim of the study was to devise a voltammetric procedure for the determination of vitamin K2 (VK2) produced by bacteria in order to find the strain that exhibits the highest efficiency of VK2 production. Bacillus subtilis, isolated from traditional Japanese food (Nattō), was chosen as a model strain. Employment of the Controlled Growth Mercury Drop Electrode (CGMDE) was crucial, as it is the only electrode that allows performing the measurement on the surface specifically renewed directly before, thus minimizing the influence of interferents. This new method was successfully applied for VK2 determination in supernatant samples. Developed procedure is robust and easily adjustable for the variety of biological matrixes. Strong differences in VK2 production depending on cultivation time were observed, but no direct correlation between the VK2 concentration in the breeding medium and the cultivation time was found. The devised protocol will be used in further measurements with different bacteria species that have the ability to produce VK2 and settle in the human intestine.Graphical abstract

Interfacial behaviour of oligodeoxynucleotides prone to G-quadruplex formation on negatively charged electrode surface monitored by electrochemical probes

Development of analytical tools enabling discrimination amongst various structures of nucleic acids attracts interest due to diverse biological functions and prospective biotechnological applications of the latter. In this work, two electrochemically active compounds, copper porphyrin complex Cu-TMPy2PP and base-modified deoxyguanosine triphosphate conjugate bearing 3-nitrophenyl moiety (dGNPTP), were used as probes to study electrode potential effects on oligodeoxynucleotides (ODNs) of various sequences and abilities to form secondary structures (including unstructured single strands, duplexes, guanine quadruplexes, i-motifs) at the surface of hanging mercury drop electrode (HMDE). Our experiments revealed formation of less dense adsorbed layers by G-rich ODNs with the propensity to fold into G-quadruplexes (G4), compared to layers formed by other studied sequences. Strikingly, the G4-forming ODNs were significantly more susceptible to desorption from the HMDE surface during its polarization to highly negative potentials compared to other ODNs. Negative potential-induced desorption of the ODNs from HMDE was further confirmed by gel electrophoresis. Application of the electrochemical probes offers a useful method for further research of DNA conformations and transitions taking place in solution and at electrically charged surfaces.

A simple electroanalytical methodology for determination of natamycin by cathodic stripping voltammetry in dairy products

ABSTRACT A cathodic stripping voltammetry method relying on the use of hanging mercury drop electrode (HMDE) was devised for determination of natamycin in dairy samples. Based on the concept of adsorptive stripping voltammetry, the possible additional effects of several metallic ions were examined in order to intensify the natamycin’s weak signal generated on HMDE. Among others, Ni(II) was the only and the most efficient ion promoting the electrochemical signal. This method is reliable and convenient to use as a routine analysis of natamycin instead of sophisticated HPLC methods. The described procedure was applied to evaluate the concentration of natamycin in cheese and yoghurt drink.

Simultaneous Determination of Metals in Cachaça: A Study on Comparison of Multivariate Methods and Quality Control

This study aims to compare multivariate calibration methods developed from data obtained by square wave anodic stripping voltammetry using a hanging mercury drop electrode for simultaneous determination of metals in cachaça, the following metals were studied: copper, zinc and cadmium. Multivariate calibration, partial least squares (PLS) and artificial neural network (ANN) methods were used in previous studies using other electrodes for this determination. In this new study, besides ANN and PLS, a hybrid model that combines PLS and NN, namely PLS-Neural was used. Also, samples of industrial cachaças were incorporated into the study in addition to artisanal samples. The quality of the methods was evaluated in terms of coefficient of determination (R2) and root mean square error of prediction (RMSEP). F test was used for comparing methods at confidence level of 95%. Based on these studies, it was found that although all methods show good results, the method employing neural networks stands out in the determination of copper in samples of cachaça. All methods proved to be fast and relatively low-cost, and they can be used for such analyses.

Voltammetric studies of the interaction of genotoxic 2-nitrofluorene with DNA

The interaction of genotoxic environmental pollutant 2-nitrofluorene (2-NF) with double-stranded DNA has been studied using a hanging mercury drop electrode (HMDE) as an electrochemical sensor. Two types of DNA damage were investigated and electrochemically detected using cyclic voltammetry and differential pulse voltammetry: (i) DNA damage caused by the direct interaction with 2-NF and (ii) DNA damage caused by short-lived radicals generated by the electrochemical reduction of 2-NF. For the study of the direct interaction, the HMDE was modified by DNA and the interaction of DNA with 2-NF was studied after their mutual interaction right at the HMDE surface, or DNA was preincubated with 2-NF in solution and, subsequently, the interaction was studied voltammetrically. Using both detection techniques, the formation of DNA–2-NF complex was observed and the mutual interaction was interpreted as an intercalation between DNA base pairs. On the basis of obtained results, we suppose that expected formation of 8-oxoguanosine leads to guanosine–cytidine base pair interruption and DNA double-strand break formation. The binding constants (K) of the DNA–2-NF complex formed in solution and on the HMDE surface (DNA/HMDE) were determined from the changes in the voltammetric peaks of the studied analyte.

Validation of Voltammetric Methods for Online Analysis of Platinum Dissolution in a Hydrogen PEM Fuel Cell Stack

Platinum dissolution in PEM fuel cells is an increasingly important indicator for the state-of-health and lifetime prediction of fuel cells in real applications. For this reason, portable online analysis tools are needed that can detect and quantify platinum with high sensitivity, selectivity, and accuracy in the product water of fuel cells. We validated the hanging mercury drop electrode (HMDE) and non-toxic bismuth film electrodes for the voltammetric determination of platinum for this purpose. Bismuth films were prepared by reductive deposition on both a glassy carbon solid state electrode and on a screen-printed electrode (film on-chip electrode). Both bismuth film electrodes could be successfully validated for the determination of platinum by adsorptive stripping voltammetry. An LOD of 7.9 μg/L and an LOQ of 29.1 μg/L were determined for the bismuth film solid state electrode, values of 22.5 μg/L for the LOD and of 79.0 μg/L for the LOQ were obtained for the bismuth film on-chip electrode. These numbers are still much higher than the results measured with the HMDE (LOD: 0.76 ng/L; LOQ: 2.8 ng/L) and are not sufficient to detect platinum in the product water of a fuel cell run in different load tests. The amount of dissolved platinum produced by a 100 W fuel cell stack upon dynamic and continuous high load cycling, respectively, was in the range of 2.9–4.1 ng/L, which could only be detected by the HMDE.

New nanoadsorbent based on magnetic iron oxide containing 1,4,7,10-tetraazacyclododecane in outer chain (Fe3O4@SiO2-cyclen) for adsorption and removal of selected heavy metal ions Cd2+, Pb2+, Cu2+

Magnetic Fe3O4@SiO2-cyclen nanoparticles were prepared and used as adsorbent for Cd2+, Pb2+ and Cu2+ from aqueous solution removal process controlled with differential pulse anodic stripping voltammetry (DPASV) and hanging mercury drop electrode (HDME). Nanomaterial was synthesised in three-step process co-precipitation of Fe3O4 core, coating with silane and N-(3-(triethoxysilyl)propyl)-1,4,7,10-tetraazacyclododecane-1-carboxamide silane functionalisation. The effectiveness of each step of the synthesis was confirmed using scanning electron microscopy (SEM), high-resolution X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (pXRD) and fourier-transform infrared spectroscopy (FT-IR) techniques. The Fe3O4@SiO2-cyclen nanoparticles were employed for Cd2+, Pb2+ and Cu2+ ions elimination from individual and mixed solutions by carrying out titration with a suspension of nanocomposites. The binding level for all ions both in the individual solutions and in the mixture was very similar at high levels. For Cd2+ and Cu2+ ions sorption efficiency level was from 83% to 89%, while for Pb2+ ions it was slightly lower at the level over 73%. In all cases, the equilibrium adsorption capacity parameter was over 1 mg/g and reached definitely higher values for individual ions solutions. The research results revealed that Fe3O4@SiO2- cyclen nanoparticles can be a promising adsorbent for magnetic heavy metal ions water treatment agents.

Direct determination of free Zn concentration in samples of biological interest

The speciation of essential metal ions in biological fluids, such as blood plasma and serum, is of fundamental importance to understand the homeostasis of these elements. The activity of metal ions such as Zn2+ in extracellular media is thought to affect their interaction with membrane-bound transporters, and thus is critical for their cellular uptake. Previous approaches to determine “free” Zn2+ (i.e. the hexa-aquo ion) are based on separation by either chromatography or ultrafiltration, or on metallochromic dyes. However, both types of approach are prone to affect the relevant equilibria. These drawbacks can be circumvented with the electroanalytical technique AGNES (Absence of Gradients and Nernstian Equilibrium Stripping), since it can measure free zinc concentration without perturbing the sample speciation. Here, a Bovine Serum Albumin (BSA) + Zn synthetic mixture and Fetal Bovine Serum (FBS) are analyzed as proof of concept. Adsorption of BSA on the surface of the Hanging Mercury Drop Electrode (HMDE), despite the advantage of its renewal, is so intense that it blocks appropriate attainment of the required equilibrium, and only estimations of [Zn2+] can be derived. In contrast, a rotating disc electrode with a thin mercury film deposited on it (TMF-RDE) is advantageous because of its small volume and enhanced mass transfer. Protein adsorption can be prevented by covering the TMF-RDE with Nafion. A free Zn concentration [Zn2+] = 2.7 nmol L−1 was found at pH 7.0, total Zn 20 μμmol L−1 and BSA 600 μμmol L−1. A sample of FBS with fixed pH 7.2 (MOPS 0.08 mol L−1) yielded [Zn2+] = 0.25 nmol L−1. This methodology opens the way to free metal concentration determinations in biological fluids.

Ultrathin ion-selective membranes for trace detection of lead, copper and silver ions

Voltammetric ion-selective electrodes (ISEs) based on poly(3-octylthiophene) (POT) in connection with ultra-thin membranes formulated with different selective receptors (i.e., ionophores) are proposed for detection of lead, copper and silver ions (Pb2+, Cu2+ and Ag+). The working mechanism of the POT-membrane electrode is based on interconnected charge transfer processes on both sides of the membrane, with the overall process depending on the electron transfer in the POT lattice ultimately linked to the ion transfer at the membrane–sample interface. This latter is demonstrated to be controlled by (i) the membrane composition and (ii) the accumulation/stripping electrochemical protocol, allowing the detection of traces of Ag+, Pb2+ and Cu2+. In the case of the Pb2+-selective electrode, the voltammogram displays several peaks that are hypothesized to correspond to different ion–ionophore stoichiometries. Following the signal related to the principal stoichiometry (1:1), a Pb2+ concentration as low as 0.1 nM is measurable. In contrast, the Cu2+- and Ag+-selective electrodes show only one peak for the corresponding ion analyte, which can be also detected at nanomolar concentrations. The results obtained with the three electrodes support their further usage for multi-ion detection in water samples through either a multi-ionophore-based electrode or multiple-electrode device. In any case, the membrane composition, in terms of the ionophore/exchanger molar ratio, is key to achieving a successful analytical application. Upcoming efforts may be directed at the replacement of traditional trace metal ion detection with the hanging mercury drop electrode to develop a more sustainable electrochemical approach without diminishing the analytical performance.