Ultra trace adsorptive stripping voltammetric determination of atrazine in soil and water using mercury film electrode

In situ mercury film electrode produced in the presence of thiocyanate has been shown extremely useful for highly sensitive adsorptive stripping voltammetric measurements of atrazine down to sub-μg L⁻¹ level. Operational parameters have been optimized and the stripping voltammetric performance has been investigated using square wave scans. The adsorptive stripping response is linear over the range of 0.5-60 μg L⁻¹ atrazine, with a detection limit of 0.024 μg L⁻¹. The method has been applied to the determination of atrazine in soil and water samples.     

An enzymeless organophosphate pesticide sensor using Au nanoparticle-decorated graphene hybrid nanosheet as solid-phase extraction

A sensitive enzymeless organophosphate pesticides (OPs) sensor is fabricated by using Au nanoparticles (AuNPs) decorated graphene nanosheets (GNs) modified glassy carbon electrode as solid phase extraction (SPE). Such a nanostructured composite film, combining the advantages of AuNPs with two dimensional GNs, dramatically facilitates the enrichment of nitroaromatic OPs onto the surface and realizes their stripping voltammetric detection of OPs by using methyl parathion (MP) as a model. The stripping voltammetric performances of captured MP were evaluated by cyclic voltammetric and square-wave voltammetric analysis. The combination of the nanoassembly of AuNPs-GNs, SPE, and stripping voltammetry provides a fast, simple, and sensitive electrochemical method for detecting nitroaromatic OPs. The stripping analysis is highly linear over the MP concentration ranges of 0.001-0.1and 0.2-1.0 μg mL⁻¹ with a detection limit of 0.6 ng mL⁻¹. This designed enzymeless sensor exhibits good reproducibility and acceptable stability.     

Glassy carbon electrodes modified with gold nanoparticles for the simultaneous determination of three food antioxidants

Electrochemical behavior of three antioxidants: butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and butylated hydroquinone (TBHQ), was investigated at a glassy carbon electrode modified with gold nanoparticles (AuNPs/GCE). This electrode was characterized by scanning electron microscopy (SEM). The experimental results indicated that the modified electrode was strongly electroactive during the redox reactions of BHA, BHT and TBHQ, and this was confirmed by the observed increased redox peak currents and shifted potentials; in addition, the oxidation products of BHA and TBHQ were found to be the same. The experimental conditions were optimized and the oxidation peaks of BHA and BHT were clearly separated. Based on this, an electrochemical method was researched and developed for the simultaneous determination of BHA, BHT and TBHQ in mixtures with the use of first derivative voltammetry; the linear concentration ranges were 0.10–1.50 μg mL⁻¹, 0.20–2.20 μg mL⁻¹ and 0.20–2.80 μg mL⁻¹, and detection limits were 0.039, 0.080 and 0.079 μg mL⁻¹, for BHA, BHT and TBHQ, respectively. The proposed method was successfully applied for the analysis of the three analytes in edible oil samples.     

Simultaneous voltammetric determination of morphine and noscapine by adsorptive differential pulse stripping method and least-squares support vector machines

An adsorptive differential pulse stripping method for the simultaneous determination of morphine and noscapine is proposed. The procedure involves an adsorptive accumulation of morphine and noscapine on a hanging mercury drop electrode (HMDE), followed by oxidation of adsorbed morphine and noscapine by voltammetric scan using differential pulse modulation. The optimum experimental conditions are: pH 10.0, accumulation potential of −100 mV versus Ag/AgCl, accumulation time of 150 s, scan rate of 40 mV s⁻¹ and pulse height of 100 mV. Morphine and noscapine peak currents were observed in same potential region at about +0.25 V. The simultaneous determination of morphine and noscapine by using voltammetry is a difficult problem in analytical chemistry, due to voltammogram interferences. The resolution of mixture of morphine and noscapine by the application of least-squares support vector machines (LS-SVM) was performed. The linear dynamic ranges were 0.01-3.10 and 0.015-2.75 μg mL⁻¹ and detection limits were 3 and 7 ng mL⁻¹ for morphine and noscapine, respectively. The capability of the method for the analysis of real samples was evaluated by the determination of morphine and noscapine in addict's human plasma with satisfactory results.     

Determination of amlodipine besylate by adsorptive square-wave anodic stripping voltammetry on glassy carbon electrode in tablets and biological fluids

The adsorptive and electrochemical behavior of amlodipine besylate on a glassy carbon electrode were explored in Britton-Robinson buffer solution by using cyclic and square-wave voltammetry. Cyclic voltammetric studies indicated the oxidation of amlodipine besylate at the electrode surface through a single two-electron irreversible step and fundamentally controlled by adsorption. The solution conditions and instrumental parameters were optimized for the determination of the authentic drug by adsorptive square-wave stripping voltammetry. Amlodipine besylate gave a sensitive adsorptive oxidation peak at 0.510 V (versus Ag/AgCl). The oxidation peak was used to determine amlodipine besylate in range 4.0×10⁻⁸ to 2.0×10⁻⁶ with a detection limit of 1.4×10⁻⁸ M. The procedure was successfully applied for the assay of amlodipine besylate in tablets (Norvasc)^®. The percentage recoveries were in agreement with those obtained by the reference method. Applicability to assay the drug in urine and serum samples was illustrated. The mean percentage recoveries were 96.31±1.18 and 96.98±1.17, respectively. The proposd method used for monotoring clinically relevant concntrations of drug in human urine and serum.     

Application of SiO2-poly(dimethylsiloxane) hybrid material in the fabrication of amperometric biosensor

A highly sensitive adsorptive stripping voltammetric protocol for measuring trace beryllium, in which the preconcentration is achieved by adsorption of the beryllium-arsenazo-I complex at a preplated mercury-coated carbon-fiber electrode, is described. Optimal conditions were found to be a 0.05 M ammonium buffer (pH 9.7) containing 5 μM arsenazo-I, an accumulation potential of 0.0 V (versus Ag/AgCl) and a square-wave voltammetric scan. The new procedure obviates the need for renewable mercury-drop electrodes used in early stripping protocols for beryllium. A linear response is observed over the 10-60 μg l⁻¹ concentration range (90 s accumulation), along with a detection limit of 0.25 μg l⁻¹ beryllium (10 min accumulation). A 15-s electrochemical cleaning enables the same mercury film to be used for a prolonged operation. High stability is thus indicated from the reproducible response of a 100 μg l⁻¹ beryllium solution (n = 60; RSD = 3.3%) over a 2.5-h operation. Applicability to a seawater sample is illustrated. The attractive behavior of the new sensor holds great promise for on-site environmental and industrial monitoring of beryllium. Preliminary data in this direction using mercury-coated screen-printed electrodes are encouraging.     

Catalytic adsorptive stripping voltammetric measurements of trace vanadium at bismuth film electrodes

Bismuth-coated glassy carbon electrodes have been successfully applied for catalytic adsorptive stripping voltammetric measurements of low levels of vanadium(V) in the presence of chloranilic acid (CAA) and bromate ion. The new protocol is based on the accumulation of the vanadium-chloranilic acid complex from an acetate buffer (pH 5.5) solution at a preplated bismuth film electrode held at −0.35 V (versus Ag/AgCl), followed by a square-wave voltammetric scan. Factors influencing the adsorptive stripping performance, including the CAA and bromate concentrations, solution pH, and accumulation potential or time have been optimized. The response compares favorably with that observed at mercury film electrodes. A linear response is observed over the 5-25 μg/L concentration range (2 min accumulation), along with a detection limit of 0.20 μg/L vanadium (10 min accumulation). High stability is indicated from the reproducible response of a 50 μg/L vanadium solution (n = 25; R.S.D. = 3.1%). Applicability to a groundwater sample is illustrated.     

Novel reductive–reductive mode electrochemical detection of Rohypnol following liquid chromatography and its determination in coffee

Rohypnol (flunitrazepam) has been successfully determined in coffee by high performance liquid chromatography dual electrode detection (LC-DED) in the dual reductive mode. Initial studies were performed to optimise the chromatographic conditions and these were found to be 50% acetonitrile, 50% 50 mM pH 2.0 phosphate buffer at a flow rate of 0.75 mL min⁻¹, employing a Hypersil C₁₈, 5 μm, 250 mm × 4.6 mm column. Cyclic voltammetric studies were made to ascertain the redox behaviour of Rohypnol at a glassy carbon electrode over the pH range 2–12. Hydrodynamic voltammetry was used to optimise the applied potential at the generator and detector cells; these were identified to be −2.4 V and +0.8 V for the redox mode and −2.4 V and −0.1 V for the dual reductive mode respectively. A linear range of 0.5–100 μg mL⁻¹, with a detection limit of 20 ng mL⁻¹ was obtained for the dual reductive mode. Further studies were then performed to identify the optimum conditions required for the LC-DED determination of Rohypnol in beverage samples. A convenient and rapid method for the determination of Rohypnol in beverage samples was developed using a simple sample pre-treatment procedure. A recovery of 95.5% was achieved for a sample of white coffee fortified at 9.6 μg mL⁻¹ Rohypnol.     

Determination of trace aluminium by adsorptive stripping voltammetry on a preplated bismuth-film electrode in the presence of cupferron

This work reports the use of adsorptive stripping voltammetry (AdSV) for the determination of aluminium on a rotating-disc bismuth-film electrode (BiFE). Al(III) ions in the non-deoxygenated sample were complexed with cupferron and the complex was accumulated by adsorption on the surface of the preplated BiFE. The stripping step was carried out by using a square-wave (SW) potential-time voltammetric excitation signal. The experimental variables as well as potential interferences were investigated and the figures of merit of the method were established. Using the selected conditions, the 3σ limit of detection for aluminium was 0.5 μg l⁻¹ at a preconcentration time of 240 s and the relative standard deviation was 4.2% at the 5 μg 1⁻¹ level for a preconcentration time of 120 s (n = 8). The accuracy of the method was established by analysing water and metallurgical samples.     

Nafion/2,2'-bipyridyl-modified bismuth film electrode for anodic stripping voltammetry

This paper describes the fabrication, characterisation and the application of a Nafion/2,2′-bipyridyl/bismuth composite film-coated glassy carbon electrode (NC(Bpy)BiFE) for the anodic stripping voltammetric determination of trace metal ions (Zn²⁺, Cd²⁺ and Pb²⁺). The NC(Bpy)BiFE electrode is prepared by first applying a 2.5 mm³ drop of a coating solution containing 0.5 wt% Nafion and 0.1% (w/v) 2,2′-bipyridil (Bpy) onto the surface of a glassy carbon electrode, while the Bi film was plated in situ simultaneously with the target metal ions at −1.4 V. The main advantage of the polymer coated bismuth film electrode is that the sensitivity of the stripping responses is increased considerably due to the incorporation of the neutral chelating agent of 2,2′-bipyridyl (Bpy) in the Nafion film, while the Nafion coating improved the mechanical stability of the bismuth film and its resistance to the interference of surfactants. The key experimental parameters relevant to both the electrode fabrication and the voltammetric measurement were optimized on the basis of the stripping signals. With a 2 min deposition time in the presence of oxygen, linear calibration curves were obtained in a wide concentration range (about 2-0.001 μM) with detection limits of 8.6 nM (0.56 μg dm⁻³) for Zn²⁺, 1.1 nM (0.12 μg dm⁻³) for Cd²⁺ and 0.37 nM (0.077 μg dm⁻³) for Pb²⁺. For nine successive preconcentration/determination/electrode renewal experiments the standard deviations were between 3 and 5% at 1.2 μM for zinc and 0.3-0.3 μM concentration level for lead and cadmium, respectively, and the method exhibited excellent selectivity in the presence of the excess of several potential interfering metal ions. The analytical utility of the stripping voltammetric method elaborated was tested in the assay of heavy metals in some real samples and the method was validated by ICP-MS technique.     

On-line stripping voltammetry of trace metals at a flow-through bismuth-film electrode by means of a hybrid flow-injection/sequential-injection system

In this work, we describe an automated stripping analyzer operating on a hybrid flow-injection/sequential-injection (FIA/SIA) mode and utilizing a bismuth-film electrode (BiFE) as a flow-through sensor for on-line stripping voltammetry of trace metals. The instrument combines the advantages of FIA and SIA and is characterised by simplicity, low-cost, rapidity, versatility and low consumption of solutions. The proposed analytical flow methodology was applied to the determination of Cd(II) and Pb(II) by anodic stripping voltammetry (ASV) and of Ni(II) and Co(II) by adsorptive stripping voltammetry (AdSV). The steps of the rather complex experimental sequence (i.e. the bismuth-film formation, the analyte accumulation, the voltammetric stripping and the electrode cleaning/regeneration) were conducted on-line and the critical parameters related to the respective analytical procedures were investigated. In ASV, for a accumulation time of 180 s the limits of detection for Cd(II) and Pb(II) were 2 and 1 μg l⁻¹, respectively (S/N = 3) and the relative standard deviations were 5.3% and 4.7%, respectively (n = 8). In AdSV, for a total sample volume of 1000 μl, the limits of detection for Ni(II) and Co(II) were 1 μg l⁻¹ (S/N = 3) and the relative standard deviations were 5.5% and 6.2%, respectively (n = 8). The measurement frequency ranged between 15 and 20 stripping cycles h⁻¹. The results indicate that the BiFE is well suited as a flow-through detector for on-line stripping analysis and, by virtue of its low toxicity, can serve as a viable alternative to mercury-based flow-through electrodes.     

Voltammetric determination of salicylic acid in pharmaceuticals formulations of acetylsalicylic acid

The electrochemical oxidation of salicylic acid (SA) has been studied on a glassy carbon electrode using cyclic voltammetry and differential pulse voltammetric (DPV) method. SA gives a single irreversible oxidation wave over the wide pH range studied. The irreversibility of the electrode process was verified by different criteria. The mechanism of oxidation is discussed. Using differential pulse voltammetry, SA yielded a well-defined voltammetric response in Britton-Robinson buffer solution, pH 2.37 at 1.088 V (versus Ag/AgCl). The method was linear over the SA concentration range: 1-60 μg ml⁻¹. The method was successfully applied for the analysis of SA as a hydrolysis product, in solid pharmaceutical formulations containing acetylsalicylic acid (ASA).     

Square-wave adsorptive stripping voltammetric approaches at two in situ modified electrodes as first analytical methods for the quantitative determination of a new anticancer drug candidate

The two adsorptive stripping voltammetric approaches for detection and quantitative determination of diethyl (2E)-2-{(2E)-[1-(4-methylphenyl)imidazolidin-2-ylidene]hydrazinylidene}butanedioate (DIB)—a novel molecule of medical importance—using two sensitive sensors based on modified glassy carbon electrodes as reusable sensors, were developed for the first time. The proposed electrochemical methods are based on adsorptive/reductive behaviour of DIB at two modified carbonic electrodes: a bismuth film-modified glassy carbon electrode (BiF/GCE) and a lead film-modified glassy carbon electrode (PbF/GCE). The electron gain mechanism for the electrochemical reduction of DIB on both developed sensors was proposed for the first time. To achieve the highest sensitivity in adsorptive stripping determinations, various experimental variables (e.g. the composition and pH of the supporting electrolytes, deposition conditions of bismuth and lead films, concentrations of plating solutions, accumulation times and potentials of DIB, etc.) were extensively examined. The comparison of validation parameters obtained during the determination of DIB at two sensors was presented. The excellent linear correlation was found between the monitored adsorptive stripping voltammetric peak current and the DIB concentration in the range of 15–600 μg L⁻¹ at an accumulation time of 30 s (with LOD = 4.2 μg L⁻¹ and LOQ = 14.0 μg L⁻¹) using the BiF/GCE as a sensor. Furthermore, the excellent linear relationship was confirmed between the monitored adsorptive stripping voltammetric peak current and the DIB concentration in the range of 9–900 μg L⁻¹ at an accumulation time of 10 s (with better LOD = 1.5 μg L⁻¹ and LOQ = 5.0 μg L⁻¹), employing the PbF/GCE as a sensor. The two optimized adsorptive stripping voltammetric approaches—as facile, sensitive, reliable and inexpensive—were successfully used as first methods for the quantitative analysis of a novel anticancer agent (DIB) in its pure pharmaceutically acceptable form. However, the practical applicability of square-wave adsorptive stripping voltammetric determination of the electroactive DIB molecule at a PbF/GCE, as the modified electrode of higher sensitivity, was presented after its successful solid phase extraction from a real serum sample.

     

Determination of Se(IV) by anodic stripping voltammetry using gold electrodes made from recordable CDs

This work presents a simple, reproducible and low cost method, employing differential pulse anodic stripping voltammetry, for determination of selenium(IV). A gold electrode obtained from recordable compact disks (CD-R) was used to evaluate the voltammetric behavior of the metallic ion in 0.1 mol L⁻¹ HClO₄. To evaluate the voltammetric behavior of Se(IV), parameters such as deposition potential and deposition time were optimized. A wide linear response range, from 0.5 to 291 ng mL⁻¹, was obtained using a 5.0 mm diameter gold electrode. Recovery tests for Se(IV) utilizing standard reference solutions provided values between 94 and 96%.     

Catalytic adsorptive stripping voltammetry versus electrothermal atomic absorption spectrometry in the determination of trace cobalt and chromium in human urine

Two methods of the determination of cobalt and chromium in human urine of non-occupationally exposed populations—highly sensitive catalytic adsorptive stripping voltammetry (CAdSV) and electrothermal atomic absorption spectrometry (ET-AAS)—are evaluated and compared. The CAdSV methods are based on adsorptive accumulation of a cobalt-nioxime (1,2-cyclohexanedione dioxime) or a chromium-DTPA (diethylenetriammine-N,N,N′,N″,N″-pentaacetic acid) complexes on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of the catalytic reduction current of the adsorbed complex in the presence of sodium nitrite in case of cobalt or in the presence of sodium nitrate in case of chromium determination. In the CAdSV procedure UV-photolysis was used for the sample pre-treatment; the ET-AAS determination did not require any separate preliminary decomposition of the analyte urine samples. The accuracy of the procedures was checked by the analysis of commercially available quality control urine samples. The detection limits (3σ) were 0.13 μg l⁻¹ for Co and 0.18 μg l⁻¹ for Cr in ET-AAS determination and 0.007 μg l⁻¹ for Co and 0.002 μg l⁻¹ for Cr in CAdSV measurements. Precision (R.S.D.) was less than 5% for both methods. The study has shown that the CAdSV is a more reliable and sensitive technique for the determination of very low cobalt and chromium contents in urine, the detection of which is not possible when using the AAS technique.     

Sensitive and stable monitoring of lead and cadmium in seawater using screen-printed electrode and electrochemical stripping analysis

Sensitive and stable monitoring of heavy metals in seawater using screen-printed electrodes (SPE) is presented. The analytical performance of SPE coupled with square wave anodic stripping voltammetry (SWASV) for the simultaneous determination of Pb and Cd in seawater samples, in the low μg L⁻¹ range, is evaluated. The stripping response for the heavy metals following 2 min deposition was linear over the concentration range examined (10-2000 μg L⁻¹) with detection limits of 1.8 and 2.9 μg L⁻¹ for Pb and Cd, respectively. The accuracy of the method was validated by analyzing metal contents in different spiked seawater samples and comparing these results to those obtained with the well-established anodic stripping voltammetry using the hanging mercury drop electrode. Moreover, a certified reference material was also used and the results obtained were satisfactory.     

Sequential injection anodic stripping voltammetry with monosegmented flow and in-line UV digestion for determination of Zn(II), Cd(II), Pb(II) and Cu(II) in water samples

A cost-effective sequential injection system incorporating with an in-line UV digestion for breakdown of organic matter prior to voltammetric determination of Zn(II), Cd(II), Pb(II) and Cu(II) by anodic stripping voltammetry (ASV) on a hanging mercury drop electrode (HMDE) of a small scale voltammetric cell was developed. A low-cost small scale voltammetric cell was fabricated from disposable pipet tip and microcentrifuge tube with volume of about 3 mL for conveniently incorporated with the SI system. A home-made UV digestion unit was fabricated employing a small size and low wattage UV lamps and flow reactor made from PTFE tubing coiled around the UV lamp. An in-line single standard calibration or a standard addition procedure was developed employing a monosegmented flow technique. Performance of the proposed system was tested for in-line digestion of model water samples containing metal ions and some organic ligands such as strong organic ligand (EDTA) or intermediate organic ligand (humic acid). The wet acid digestion method (USEPA 3010a) was used as a standard digestion method for comparison. Under the optimum conditions, with deposition time of 180 s, linear calibration graphs in range of 10-300 μg L⁻¹ Zn(II), 5-200 μg L⁻¹ Cd(II), 10-200 μg L⁻¹ Pb(II), 20-400 μg L⁻¹ Cu(II) were obtained with detection limit of 3.6, 0.1, 0.7 and 4.3 μg L⁻¹, respectively. Relative standard deviation were 4.2, 2.6, 3.1 and 4.7% for seven replicate analyses of 27 μg L⁻¹ Zn(II), 13 μg L⁻¹ Cd(II), 13 μg L⁻¹ Pb(II) and 27 μg L⁻¹ Cu(II), respectively. The system was validated by certified reference material of trace metals in natural water (SRM 1640 NIST). The developed system was successfully applied for speciation of Cd(II) Pb(II) and Cu(II) in ground water samples collected from nearby zinc mining area.     

Selective and sensitive hydroxypropyl-beta-cyclodextrin based sensor for simple monitoring of (+)-catechin in some commercial drinks and biological fluids

(+)-Catechin (CAT) was considered as a polyphenolic compound abundantly contained in plants. It exerts protective effect against cancer, inflammatory and cardiovascular diseases. These protective effects are mainly attributed to its antioxidative activity by scavenging free radicals. Therefore, the need of simple, selective and sensitive monitoring of (+)-catechin in commercial drinks and biological fluids is crucial. A new selective and sensitive voltammetric quantification of (+)-catechin was investigated at low cost hydroxypropyl-beta-cyclodextrin modified carbon paste sensor in acidic solutions. The constructed sensor was treated in simple and fast manner to increase its stability for catechin determination. The effect of solution and instrumental parameters was investigated by using osteryoung square-wave anodic voltammetry (OSWAV) at pH 2.20 and differential pulse cathodic voltammetry (DPCV) at pH 4.40 in 0.10 M Britton-Robinson buffer. Acidic solutions were chosen to increase the stability of (+)-catechin, reduce its adsorption on the sensor surface and increase the selectivity of proposed method. Cyclic voltammetry (CV) was used to elucidate the electrochemical mechanism of catechin at the modified electrochemical sensor. A linear range up to 7.20 and 4.20 μg mL⁻¹ of catechin was achieved in anodic and cathodic voltammetry, respectively. The method gave reproducible and reliable results with 1.50 (g mL⁻¹ catechin (S.D. 0.062). Limit of detection of 0.12 and 0.30 ng mL⁻¹ and limit of quantification (LOQ) of 1.10 and 2.80 ng mL⁻¹ were easily achieved using anodic and cathodic voltammetry, respectively. Selectivity of the proposed procedure was estimated by testing recovery and adding the most interfering metal ions and/or organic compounds. The proposed method was applied successfully to selective determination of catechin in some commercial drinks like tea, cocoa and coffee with acceptable recovery range (98-102%). The extraction of catechin was rather simple, making it suitable for studies with a large number of commercial samples. Furthermore, the application to urine samples without pretreatment was achieved and statistically confirmed at 95% confidence level. It was easy to analyze catechin in urine down to 0.55 ng mL⁻¹.     

Bucky-gel coated glassy carbon electrodes, for voltammetric detection of femtomolar leveled lead ions

Femtomolar (fM) leveled lead ions were electrochemically detected using a bucky-gel coated glassy carbon electrode and differential pulse anodic stripping voltammetry. The bucky-gel was composed of dithizone, ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate), and multi-walled carbon nanotubes (MWCNTs). The fabrication of the bucky-gel coated electrode was optimized. The modified electrode was characterized with voltammetry, electrochemical impedance spectroscopy, and chronoamperometry. After the accumulation of lead ions into the bucky-gel modified electrode at −1.2 V vs. saturated calomel electrode (SCE) for 5 min in a pH 4.4 sodium acetate-acetate acid buffer solution, differential pulse anodic stripping voltammograms of the accumulated lead show an anodic wave at −0.58 V. The anodic peak current is detectable for lead ions in the concentration range from 1.0 μM down to 500 fM. The detection limit is calculated to be 100 fM. The proposed method was successfully applied for the detection of lead ions in lake water.     

Bismuth-dispersed xerogel-based composite films for trace Pb(II) and Cd(II) voltammetric determination

We report for the first time the synthesis of bismuth-modified (3-mercaptopropyl) trimethoxysilane (MPTMS) and its application for the determination of lead and cadmium by anodic stripping voltammetry. Xerogels made from bismuth-modified MPTMS and mixtures of it with tetraethoxysilane, under basic conditions (NH₃·H₂O), were characterized with scanning electron microscopy, energy dispersive spectroscopy, infrared spectroscopy and electrochemical methods. Bismuth-modified xerogels were mixed with 1.5% (v/v) Nafion in ethanol and applied on glassy carbon electrodes. During the electrolytic reductive deposition step, the bismuth compound on the electrode surface was reduced to metallic bismuth. The target metal cations were simultaneously reduced to the respective metals and were preconcentrated on the electrode surface by forming an alloy with bismuth. Then, an anodic voltammetric scan was applied in which the metals were oxidized and stripped back into the solution; the voltammogram was recorded and the stripping peak heights were related to the concentration of Cd(II) and Pb(II) ions in the sample. Various key parameters were investigated in detail and optimized. The effect of potential interferences was also examined. Under optimum conditions and for preconcentration period of 4 min, the 3σ limit of detection was 1.3 μg L⁻¹ for Pb(II) and 0.37 μg L⁻¹ for Cd(II), while the reproducibility of the method was 4.2% for lead (n = 5, 10.36 μg L⁻¹ Pb(II)) and 3.9% for cadmium (n = 5, 5.62 μg L⁻¹ Cd(II)). Finally, the sensors were applied to the determination of Cd(II) and Pb(II) ions in water samples.