Suitability of Stripping Chronopotentiometry for Heavy Metal Speciation Using Hydrogen Peroxide as Oxidant: Application to the Cd(II)‐EDTA‐PMA System

The possibilities of stripping chronopotentiometry (SCP) for heavy metal speciation have been tested in the modality of chemical oxidation using the model systems Cd(II)‐polyacrylic acid (PMA), Cd(II)‐EDTA and Cd(II)‐PMA‐EDTA. The use of 0.03% H₂O₂ as a chemical oxidant provides reliable results from transition times, but peak potentials are dramatically affected by the presence of this reagent. The study suggests that chemical‐oxidation SCP can be a technique complementary to other stripping modalities in the study of inert and macromolecular labile metal complexes.     

Stripping Chronopotentiometry and Stripping Voltammetry of Mixtures of Heavy Metal Ions Producing Close Signals: The Cd(II)‐Pb(II)‐Phthalate System

The effects of the proximity of the signals of two heavy metal ions in stripping voltammetry (SV) and constant‐current stripping chronopotentiometry (SCP) is studied at mercury drop (HMDE) and mercury film (MFE) electrodes. For this purpose, the Cd(II)‐Pb(II)‐phthalate system is used, taking advantage of the approaching of the signals corresponding to Cd(II)‐phthalate and Pb(II)‐phthalate labile complexes as phthalate is added to mixtures of Cd(II) and Pb(II)‐ions. The results are compared with those obtained by differential pulse polarography (DPP) and by stripping measurements on the Pb(II)‐phthalate system alone, showing discrepancies in SCP data under nondepletive conditions and negligible differences in the other cases.     

Developing On-Site Trace Level Speciation of Lead,Cadmium and Zinc by Stripping Chronopotentiometry (SCP): Fast Screening and Quantification of Total Metal Concentrations

Electrochemical stripping techniques are interesting candidates for carrying out onsite speciation of environmentally relevant trace metals due to the existing low-cost portable instrumentation available and the low detection limits that can be achieved. In this work, we describe the initial analytical technique method development by quantifying the total metal concentrations using Stripping Chronopotentiometry (SCP). Carbon paste screen-printed electrodes were modified with thin films of mercury and used to quantify sub-nanomolar concentrations of lead and cadmium and sub-micromolar concentrations of zinc in river water. Low detection limits of 0.06 nM for Pb(II) and 0.04 nM for Cd(II) were obtained by the standard addition method using a SCP deposition time of 180 s. The SCP results obtained for Pb(II) and Cd(II) agreed with those of inductively coupled plasma mass spectrometry (ICP-MS). The coupling of SCP with screen-printed electrodes opens up excellent potential for the development of onsite speciation of trace metals. Due to the low analysis throughput obtained for the standard addition method, we also propose a new, more rapid screening Cd(II) internal standard methodology to significantly increase the number of samples that can be analyzed per day.     

Mercury Films on Commercial Carbon Screen‐Printed Devices for the Analysis of Heavy Metal Ions: a Critical Evaluation

The suitability of mercury films on commercial screen‐printed electrodes for the analysis of heavy metal ions is critically tested for the particular case of Pb(II)‐ions. Although determination is possible by anodic stripping voltammetry with a reasonable detection limit (8.9 µg L^?1), important drawbacks are noticed as a consequence of the heterogeneous deposition of mercury on the rough surface of screen‐printed devices.     

Sensitive Stripping Determination of Cadmium(II) and Lead(II) on Disposable Graphene Modified Screen‐Printed Electrode

In the present work, a sensitive, facile and disposable sensing platform for trace analysis of heavy metal ions was developed at the Bi modified graphene‐poly(sodium 4‐styrenesulfonate) composite film screen printed electrode (GR/PSS/Bi/SPE). The GR/PSS/Bi/SPE improved sensitivity and linearity due to the functionalization of graphene with negatively charged PSS providing more absorbing sites. The detection limit of the GR/PSS/Bi/SPE is found to be 0.042 µg L^?1 for Cd²⁺ and 0.089 µg L^?1 for Pb²⁺ with linear responses of Cd²⁺ and Pb²⁺ in the range of 0.5–120 µg L^?1. Finally, the practical application was confirmed in real water with satisfactory results.     

Determination of Lead(II) Using Screen‐Printed Bismuth‐Antimony Film Electrode

This work presents a disposable bismuth‐antimony film electrode fabricated on screen‐printed electrode (SPE) substrates for lead(II) determination. This bismuth‐antimony film screen‐printed electrode (Bi‐SbSPE) is simply prepared by simultaneously in situ depositing bismuth(III) and antimony(III) with analytes on the homemade SPE. The Bi‐SbSPE can provide an enhanced electrochemical stripping signal for lead(II) compared to bismuth film screen‐printed electrodes (BiSPE), antimony film screen‐printed electrodes (SbSPE) and bismuth‐antimony film glassy carbon electrodes (Bi‐SbGC). Under optimized conditions, the Bi‐SbSPE exhibits attractive linear responses towards lead(II) with a detection limit of 0.07 µg/L. The Bi‐SbSPE has been demonstrated successfully to detect lead in river water sample.     

Facile and Simultaneous Stripping Determination of Zinc,Cadmium and Lead on Disposable Multiwalled Carbon Nanotubes Modified Screen‐Printed Electrode

Screen‐printed electrodes (SPEs) are cheap and disposable. But their application for heavy metal detection is limited due to the low sensitivity and poor selectivity. Here we report the ultrasensitive and simultaneous determination of Zn²⁺, Cd²⁺ and Pb²⁺ on a multiwalled carbon nanotubes and Nafion composite modified SPE with in situ plated bismuth film (MWCNTs/NA/Bi/SPE). The linear curves range from 0.5–100 µg L^?1 for Zn²⁺ and 0.5–80 µg L^?1 for Cd²⁺. Uniquely, the linear curve for Pb²⁺ ranges from 0.05–100 µg L^?1 with a detection limit of 0.01 µg L^?1. The practical application was verified in real samples with satisfactory results.     

Uric Acid Determination by Adsorptive Stripping Voltammetry on Multiwall Carbon Nanotubes Based Screen‐Printed Electrodes

A sensitive electroanalytical methodology for the determination of uric acid in real samples using adsorptive voltammetry at a multiwalled carbon nanotubes (MWCNT) modified screen printed electrode (SPCE) is presented. Adsorption of uric acid takes place at open circuit potential at an optimized pH 5.0. Studies about the effect of accumulation time and scan rate on the analytical signal were developed and confirm the adsorption nature of the electrodic process. Quantitative analysis of uric acid by using its oxidation process at +0.18 V (vs. an Ag pseudoreference electrode) was carried out with an accumulation time of 5 min. Thus, a linear voltammetric based reproducible determination of uric acid (RSD 5 %) in the range 1–100 µM was obtained. The method was then successfully used for the determination of uric acid in real clinical samples of urine without detection of interferences. The proposed methodology only requires a dilution of the real sample and present advantages as low cost and easy handling for non specialized technicians.     

Voltammetric Determination of Pb,Cu and Hg in Biodiesel Using Gold Screen‐printed Electrode: Comparison of Batch‐injection Analysis with Conventional Electrochemical Systems

This article compares the use of batch‐injection analysis (BIA) with a conventional batch system for the anodic stripping voltammetric (ASV) determination of Pb, Cu and Hg in biodiesel using screen‐printed gold electrode (SPGE). The optimized BIA conditions were 200 µL of injection volume of the digested samples at 5 µL s^?1 directly on the working electrode of the SPGE immersed in 0.1 mol L^?1 HCl solution. Therefore, BIA‐ASV presented the advantages of low sample consumption, which extended the SPGE lifetime to a whole working day of analyses, and potential for on‐site analysis using battery‐powered micropipettes and potentiostats. Although presenting lower sensitivity than conventional systems, the BIA‐ASV presented detection limit values of 1.0, 0.5 and 0.7 µg L^?1, respectively for Pb, Cu and Hg, a linear range between 20 and 280 µg L^?1, and adequate recovery values (90–110 %) for spiked biodiesel samples.     

Catalytic Adsorptive Stripping Chronopotentiometry of Co(II)‐DMG‐Bromate System at an In Situ Plated Lead Film Electrode

A novel catalytic adsorptive stripping chronopotentiometric (CC‐CAdSCP) procedure for the determination of Co(II) traces was developed using a lead film electrode (PbFE). The PbFE was generated in situ on a glassy carbon support from a 0.1 M ammonia buffer containing 1×10^?5 M Pb(II), 6.5×10^?5 M DMG and the target metals. An addition of 0.2 M NaBrO₃ to the solution yielded an 11‐fold catalytic enhancement of chronopotentiometric response of the Co(II)‐DMG complex. The CC‐CAdSCP curves were well‐developed, sharp and reproducible (RSD 5.0 % for 5×10^?9 M Co(II)). The limit of detection for Co(II) for 210 s of accumulation time was 4×10^?10 M (0.024 µg L^?1). In addition, the elaborated method allowed the simultaneous quantification of Co(II) and Ni(II) simultaneously.     

Microliter Volume Determination of Cosmetic Mercury with a Partially Crosslinked Poly(4‐vinylpyridine) Modified Screen‐Printed Three‐Electrode Portable Assembly

We successfully demonstrated microliter (μL) volume determination of Mercury (Hg) using an in‐built screen‐printed three electrodes containing partially crosslinked poly(4‐vinlylpyridine) (designated as pcPVP) modified carbon‐working, carbon‐counter, and Ag⁺‐quasireference electrodes (SPE/pcPVP) in a pH 4 acetate buffer solution with 2 M KCl by using the square wave anodic stripping voltammetric (SWASV) technique. Instrumental and solution phase conditions were systematically optimized. Experiments were carried out by simply placing a 500 μL‐droplet of Hg containing real sample mixed with the base electrolyte on the SPE/pcPVP surface. The SPE/Ag⁺ quasi‐reference system shifted the Hg‐SWASV detection potential ca. 250 mV positive, but the quantitative current values were appreciably similar to that of a standard Ag/AgCl reference electrode. Under optimal condition, the calibration graph is linear in the window of 100–1000 ppb of the Hg droplet system with a detection limit of 69.5 ppb (S/N=3). Finally real sample assays were demonstrated for prohibited cosmetic Hg containing skin‐lightening agents in parallel with ICP‐OES measurements.     

Adsorptive Stripping Voltammetric Determination of 4‐Hexylresorcinol in Pharmaceutical Products Using Multiwalled Carbon Nanotube Based Electrodes

A sensitive electroanalytical method is presented for the determination of 4‐hexylresorcinol using adsorptive stripping voltammetry (AdsSV) at a multiwalled carbon nanotube modified basal plane pyrolytic graphite electrode (MWCNT‐BPPGE). This method is also extended to the use of a MWCNT modified screen‐printed electrode (MWCNT‐SPE), thereby demonstrating that this approach can easily be incorporated into a facile and inexpensive electrochemical sensor.     

Voltammetric Determination of Pb(II) and Cd(II) Ions in Well Water Using a Sputtered Bismuth Screen‐Printed Electrode

A method using commercially available sputtered bismuth screen‐printed electrodes (Bi_spSPE), as substitute to mercury electrodes, for the determination of trace Pb(II) and Cd(II) ions in drinking well water samples collected in a contaminated area in The Republic of El Salvador by means of differential pulse anodic stripping voltammetry (DPASV) has been proposed. The comparable detection and quantification limits obtained for both Bi_spSPE and hanging mercury drop electrode (HMDE), together with the similar results with a high reproducibility obtained in these water samples analyses recommend the applicability of Bi_spSPE for the determination of low level of metal concentrations in natural samples.     

Stripping Analysis of As(III) by Means of Screen‐Printed Electrodes Modified with Gold Nanoparticles and Carbon Black Nanocomposite

A novel sensor based on carbon black‐gold nanoparticle nanocomposite modified screen‐printed electrode (CB‐AuNPs/SPE) for the detection of As(III) has been developed. The sensor was prepared modifying the SPE with CB and AuNPs by a drop casting automatable deposition. The As(III) was detected by CB‐AuNPs/SPE using anodic stripping voltammetry, with a high sensitivity (673±6 µA µM^?1 cm^?2) and reaching a LOD of 0.4 ppb. Finally, CB‐AuNPs/SPE has been applied to As(III) trace analysis in drinking water, obtaining satisfactory recovery values (99±9 %).     

The Electrochemical Behavior of Nitrazepam at a Screen‐Printed Carbon Electrode and Its Determination in Beverages by Adsorptive Stripping Voltammetry

The cyclic voltammetric behavior of nitrazepam was investigated at screen‐printed carbon electrodes over the range ?1.5 V to +1.5 V. Two reduction peaks were observable on the negative scan, at ?0.7 V, and ?1.2 V using pH 6 buffer. On the return scan a single oxidation peak was obtained at ?0.05 V. For quantitative analysis of beverages, we developed an anodic adsorptive stripping voltammetric method which required only dilution with buffer. The identification of nitrazepam and flunitrazepam could be achieved using cyclic voltammetry.     

Ex‐situ Antimony Screen‐printed Carbon Electrode for Voltammetric Determination of Ni(II)‐ions in Wastewater

An Ex‐situ antimony film screen‐printed carbon electrode (Ex‐situ SbSPCE) was successfully applied for the determination of Ni(II), by means of adsorptive stripping voltammetry using dimethylglyoxime as complexing agent, in a certified reference wastewater sample. This electrode is proposed as an alternative to more conventional antimony film electrodes. Ex‐situ SbSPCE was analytically characterized and the obtained parameters suggest that Ex‐situ SbSPCE behaves much better than both Ex‐situ BiSPCE and Bi_spSPE for Ni(II) determination. The results confirm the applicability of Ex‐situ SbSPCE for the determination of low concentration levels of Ni(II) in natural samples with a very high reproducibility and good trueness.     

Anodic Stripping Voltammetry Combined with Sequential Injection Analysis for Measurements of Trace Metal Ions with Bismuth‐ and Antimony Film Electrodes under Comparable Conditions

Anodic stripping voltammetry combined with sequential injection analysis (ASV‐SIA) was selected to examine the use of bismuth‐ and antimony‐film plated glassy carbon electrodes under comparable conditions for the determination of Pb(II) and Cd(II) ions. Of interest were the conditions for film deposition, as well as the composition of sample/carrier solutions, including concentrations of Sb(III) or Bi(III) and HCl. Then, by the optimized procedure, one could determine Pb(II), Cd(II), and Zn(II) ions at the low µg L^?1 level and ASV‐SIA configuration with both electrodes tested on analysis of a water sample.     

Simultaneous Quantitative Determination of Cadmium,Lead, and Copper on Carbon‐Ink Screen‐Printed Electrodes by Differential Pulse Anodic Stripping Voltammetry and Partial Least Squares Regression

Water is a vital commodity for every living entity on the planet. However, water resources are threatened by various sources of contamination from pesticides, hydrocarbons and heavy metals. This has resulted in the development of concepts and technologies to create a basis for provision of safe and high quality drinking water. This paper focuses on the simultaneous quantitative determination of three common contaminants, the heavy metals cadmium, lead and copper. Multivariate calibration was applied to voltammograms acquired on in‐house printed carbon‐ink screen‐printed electrodes by the highly sensitive electrochemical method of differential pulse anodic stripping voltammetry (DPASV). The statistically inspired modification of partial least squares (SIMPLS) algorithm was employed to effect the multivariate calibration. The application of data pretreatment techniques involving range‐scaling, mean‐centering, weighting of variables and the effects of peak realignment are also investigated. It was found that peak realignment in conjunction with weighting and SIMPLS led to the better overall root mean square error of prediction (RMSEP) value. This work represents significant progress in the development of multivariate calibration tools in conjunction with analytical techniques for water quality determination. It is the first time that multivariate calibration has been performed on DPASV voltammograms acquired on carbon‐ink screen‐printed electrodes.     

New Screen‐Printed Ion‐Selective Electrodes for Potentiometric Titration of Cetyltrimethylammonium Bromide in Different Civilic Media

The performance of home‐made printed carbon ink in the fabrication of a simple screen‐printed carbon paste electrodes (SPCPEs) was studied. Such electrodes are applied for the potentiometric titration and hence determination of cetyltrimethylammonium bromide (CTAB) in different pharmaceuticals and water samples. The performances of the new screen printed electrodes towards CTAB are compared with those for carbon paste, coated‐wire, coated graphite and polyvinyl chloride electrodes. SPCPEs have been successfully used for the potentiometric titration of CTAB in the analytical grad solutions, with a potential jump amounts to 1050 mV. The effect of plasticizer type, carbon content, binding materials, printing ink formulation, response time and printing process are optimized. The method is applied for pharmaceutical preparations with a percentage recovery of 99.20 % and RSD=0.45. The electrodes passes a near‐Nernstian cationic slope of 58.70±1.3 and 56.32±2.4 mV and lower detection limit of 6.8×10^?7 and 5.80×10^?7 M with a reproducibility of 0.145 and 3.25 % and response time of about 3 s and exhibit adequate shelf‐life of 6 and 2 months for SPCPE and CPE, respectively. The frequently used CTAB of analytical and technical grade as well as different water samples has been successfully titrated and the results obtained agreed with those obtained with commercial electrode and standard two phase titration method. The sensitivity of the proposed method is comparable with the official method indicating its possibility to be used in field measurements.     

Electrochemical Determination of Pyrogallol at Conducting Poly(3,4‐ethylenedioxythiophene) Film‐Modified Screen‐Printed Carbon Electrodes

The electrochemical oxidation of pyrogallol at electrogenerated poly(3,4‐ethylenedioxythiophene) (PEDOT) film‐modified screen‐printed carbon electrodes (SPCE) was investigated. The voltammetric peak for the oxidation of pyrogallol in a pH 7 buffer solution at the modified electrode occurred at 0.13 V, much lower than the bare SPCE and preanodized SPCE. The experimental parameters, including electropolymerization conditions, solution pH values and applied potentials were optimized to improve the voltammetric responses. A linear calibration plot, based on flow‐injection amperometry, was obtained for 1–1000 µM pyrogallol, and a slope of 0.030 µA/µM was obtained. The detection limit (S/N=3) was 0.63 µM.