Hanging Mercury Drop Electrode Research Articles

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.

(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).

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.

Free and bound histidine in reactions at mercury electrode

The intrinsic electrochemical activity of some amino acids as well as their residues in peptides and proteins at mercury electrodes can be utilized for fundamental research purposes and for the development of label-free reagentless analytical methods. Here we present a new concept of how to investigate free histidine (His) and how to detect its residues within the more complex structures of some peptides and proteins at a hanging mercury drop electrode. The approach is based on the ability of the deprotonated His imidazole group to oxidize the electrode mercury at potentials less positive than those of the electrolytic (anodic) dissolution of mercury. Using cyclic voltammetry, we found that in a weakly alkaline solution of free His or bound in His homohexapeptide, the oxidative formation and the reductive cleavage of the bond between the imidazole group and the electrode mercury are reversible and take place in an adsorbed state. In addition to free His and His homohexapeptide, also more complex heteropeptide samples such as angiotensin peptides, a modified fragment of amyloid β peptide, and His-tagged mutant protein α-synuclein A53T were investigated by constant-current chronopotentiometry in neutral solution. The proposed methodology could be further applied for the investigation of the acid-base and metal chelating properties of His-containing peptides or proteins, and for the study of their structural changes and interactions with other substances.

Local diffusion indicators: A new tool for analysis of electrochemical mass transport

• Numerical simulation of chronoamperometry on a plane-truncated sphere is performed. • A local diffusion indicator is introduced. • Linear, convergent and thin layer diffusion contributions to flux are identified. • Otherwise indistinguishable diffusional processes are resolved. The recently introduced diffusion indicator (Haonan et al, J. Electroanal. Chem., 2019, 855, 113602) is generalised to characterise local mass transport fluxes to a non-uniformly accessible electrode to probe both qualitatively and quantitatively the nature of the diffusion to different parts of an electrode surface at different times following electrochemical perturbation. The approach is illustrated in respect of diffusion to a truncated sphere on a plane surface. The relative contributions of thin layer, linear and convergent diffusion following potential step chronoamperometry are evaluated. Comparison is made with analogous measurements on a micro-disc electrode. The results have implications for the transients accompanying the impact of nanoparticles on planar electrodes and for hanging mercury drop electrodes.

Metal‐free phthalimide‐labeled peptide nucleic acids for electrochemical biosensing applications

AbstractPeptide nucleic acids (PNAs) are neutral mimics of natural DNA and RNA biopolymers that have caught the attention of researchers working on the identification of specific sequences of nucleobases in DNA/RNA strands. For this purpose, specific analytical protocols need to be developed to optimize the nucleic acid recognition ability of PNAs, exploiting both the high intrinsic affinity of PNA/DNA(RNA) couples as well as suitable markers, either linked to the PNA backbone or properly interacting with it in the working medium. In this context, the paper reports on phthalimide and 4‐nitrophthalimide as two cheap, metal‐free electroactive markers covalently bound to the pseudo‐peptide backbone of a PNA decamer. After a preliminary characterization of the markers, as such and in PNA conjugates, attention has been moved toward the optimization of the detectability of the labeled PNA decamers in aqueous solutions. Exploiting the potentiometric stripping analysis on hanging mercury drop electrode it has been possible to reach satisfactory detection limits of ca. 10 nM avoiding the use of expensive transition metal complexes as labels and/or of co‐reagents.

Simultaneous Determination of Amlodipine and Irbesartan in their Pharmaceutical Formulations by Square-Wave Voltammetry.

Hypertension is one of the most important health problems in the world and irbesartan and amlodipine are used in combination in various dosages for the treatment of high blood pressure. The aim of this study is to develop a fast, easy, sensitive, accurate, and precise squarewave voltammetry method for simultaneous determination of irbesartan and amlodipine besylate from pharmaceutical formulations at a hanging mercury drop electrode. In the applied method, since both active substances gave a peak at different potentials, no interference occurred between them. In optimization studies, Britton-Robinson buffer of pH 8.0 was chosen, in which the most appropriate peak shape and maximum peak current were observed. At the same time, as a result of instrumental parameter optimization to obtain reproducible results, 6 mV for scan increment, 30 mV for pulse amplitude, and 50 Hz for frequency were found suitable. As a result of the calibration studies of the optimized method, linear working ranges were determined as 1.00-13.08 μg mL-1 for irbesartan and 5.83-16.51 μg mL-1 for amlodipine besylate. Limit of detection and limit of quantitation values were respectively calculated as 0.63 and 1.00 μg mL-1 for irbesartan and 0.50 and 1.98 μg mL-1 for amlodipine besylate. The results of precision values (RSD) ranged from 0.67% to 2.31% for irbesartan and 0.65% to 1.49% for amlodipine besylate. Accuracy values were calculated as -0.15% to 1.63% for irbesartan and -0.07% to 3.78% for amlodipine besylate. The results obtained from the recovery studies ranged from 101.05% to 102.78% and from 98.88% to 102.20% for amlodipine besylate and irbesartan, respectively. After the validation studies of the developed method were carried out, it was successfully applied to pharmaceutical formulations containing these active substances.

Ion Exchange Resin Modified Carbon Paste Electrode Applied to Simultaneous Determination of Cd (II) and Pb (II)

A new, simple, sensitive and fast analytical method was developed to simultaneous quantification of Cd(II) and Pb(II) in cooling water by anodic square wave redissolution voltammetry (SWASV) using a modified carbon paste electrode composite with carbon black, resin functionalized with sulphonic group and paraffin. The experimental conditions such as supporting electrolyte (composition, pH and ionic strength) and SWASV parameters were optimized. The best conditions of Cd(II) and Pb(II) (higher peak current) were obtained in 0.1 mol l−1 BR buffer (pH 4.6) from −1.1 to 0.3 V, amplitude of 60 mV, frequency of 40 Hz, potential step of 5 mV, potential and deposition time of −1.1 V and 240 s, respectively. The analytical curve of Cd(II) and Pb were linear from 10 to 50 μg l−1 (R2 = 0.999) with quantification limit of 0.06 and 0.12 μg l−1, respectively. The method was successfully applied in cooling water from thermoelectric industry and the concentrations of Cd(II) and Pb(II) were 3.27 ± 0.30 and 2.80 ± 0.18 mg l−1, respectively. The method accuracy was evaluated through the comparison with the comparative method (SWV with Hanging Mercury Drop Electrode) and the relative error obtained was smaller than 9.8%.

Study of electrochemical behavior of two chemically similar acridines: Tacrine and 9-aminoacridine on hanging mercury drop electrode

ABSTRACT. The electrochemical behavior of two chemically related acridine compounds: tacrine (TAC) and 9-aminoacridine (9-AA) was investigated on a hanging mercury drop electrode (HDME). The electrochemical study was carried out by using Osteryoung square wave voltammetry (OSWV) and cyclic voltammetry (CV) techniques in the Britton-Robinson (B-R) buffer solution at pH = 2.0–12.0, KCl (0.1/0.2/0.3 M) and methanol (0.0-50%) mixture as supporting electrolyte. TAC showed maximum current at pH 7.5 while 9-AA at pH 10, KCl (0.3M), and 10% methanol. The study of electrochemical reduction of 9-AA and TAC on the HDME by using CV resulted in a quasi-reversibility, mainly diffusion-controlled reaction. The reaction involved 1e–/1H+ reduction at nitrogen atom in the case of the 9-AA while the second process involved the 2e–/2H+ reduction of the intra-cyclic azomethine group. The reduction peak potential of structurally related acridine compounds is influenced by the pH values and percentage of the organic solvent of the supporting electrolytes. Also, the study may provide insight into the electron transfer pathways of biological reactions of the acridines and their electrochemical behavior on the electrode.
 
 KEY WORDS: Tacrine, 9-Aminoacridine, Cyclic voltammetry, Osteryoung square wave voltammetry, Hanging mercury dropping electrode
 
 Bull. Chem. Soc. Ethiop. 2021, 35(3), 639-646.
 DOI: https://dx.doi.org/10.4314/bcse.v35i3.14

Indirect Electrochemical Determination of Chlorpropamide Through Its Interaction with Valsartan Using Square Wave Voltammetry

A square wave voltammetric technique coupled with three electrode detection system consist of hanging mercury drop electrode (HMDE) as working electrode, 1mm platinum wire as an auxiliary electrode (Pt-wire) and silver/silver chloride saturated potassium chloride (Ag/AgCl.sat.KCl) as reference electrode was used to determine the chlorpropamide indirectly through its interaction with valsartan, chlorpropamide gives no reduction peaks in the studied range. The effect of pH and the stability of the measurement were examined calibrations curve of chlorpropamide was constructed and the relation between current and concentration of chlorpropamide was linear with R2 value = 0.9944. The limit of detection for chlorpropamide was 4.89 x 10-9 M through its interaction with valsartan.

Voltammetric studies of selected porphyrin G-quadruplex ligands and their interaction with DNA in solution and at the mercury electrode surface

With the increasing interest in DNA G-quadruplexes (G4) as important regulatory elements and prospective therapeutical targets, DNA structure-sensitive electrochemical methods can be advantageously used for studying of their structure or screening for interactions with G4 ligands developed as candidate drugs. Porphyrin derivatives are among the most prominent classes of G4 ligands. Interactions of porphyrins H2-TMPy2PP and Cu-TMPy2PP with oligodeoxynucleotides (ODNs) either forming or not forming G4 were investigated in this work. For this purpose, cyclic voltammetry at hanging mercury drop electrode (HMDE) complemented by UV-vis and CD spectroscopy was applied. Both porphyrins were found to interact strongly with G4 in solution by UV-vis titrations. However, Cu-TMPy2PP appears to interact also with double-stranded and single-stranded ODNs. Accordingly, cyclic voltammetry was able to distinguish between free and ODN-bound forms of Cu-TMPy2PP, but not between binding of the ligand to ODNs with or without G4 propensity.

Thallium: A Polluting Metal of New Generation. Its Voltammetric Determination in Herbal Medicines in Presence of Metal Interferences

The present paper reports a new application: the voltammetric determination in herbal medicines of ultra-trace thallium(I), in the presence of lead(II), tin(II) and antimony(III) as interfering metals, by square wave anodic stripping voltammetry (SWASV). A conventional three-electrodes voltammetric cell was employed with a stationary hanging mercury drop electrode (HMDE) as working electrode and a platinum electrode and an Ag|AgCl|KClsatd. electrode as auxiliary and reference electrodes, respectively. The supporting electrolyte was 0.5 mol L−1 ammonium citrate buffer pH 6.5 + 7.3·10−3 mol L−1 EDTA-Na2. The analytical procedure was verified by the analysis of the standard reference materials: spinach Leaves NIST-SRM 1570a and tomato leaves NIST-SRM 1573a from National Institute of Standards and Technology. Precision and trueness, expressed as relative standard deviation and relative error, respectively, were generally lower than 7% in all cases. Once set up on the standard reference materials, the analytical procedure was transferred and applied to herbal medicines samples—Taraxacun officinale weber, Eucalyptus globulus and Harpagophytum procumbens DC—sold on the market. A critical comparison with spectroscopic measurements is also discussed.