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.     

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.     

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.     

Voltammetric Determination of Neonicotinoid Pesticides at Disposable Screen‐Printed Sensors Featuring a Sputtered Bismuth Electrode

This work reports the determination of 5 neonicotinoid pesticides (Clothianidin, Imidacloprid, Thiamethoxam, Nitenpyram and Dinotefuran) in water samples by cathodic differential pulse (DP) voltammetry at screen‐printed disposable sensors featuring a sputtered bismuth thick‐film working electrode, a Ag reference electrode and a carbon counter electrode. The performance of the bismuth thick‐film electrodes was compared to that of a home‐made bismuth thin‐film electrode and a bismuth‐bulk electrode. The electrodes were further characterized by electrochemical and optical techniques. The effect of the pH of the supporting electrolyte on the DP reduction currents of the 5 pesticides was studied. The limits of quantification (LOQs) in 4 water matrices (distilled water, tap water, mineral water and surface water) were in the range 0.76 to 2.10 mg L^?1 but severe matrix effects were observed in the analysis of mineral and, especially, surface water samples. Using a solid‐phase extraction (SPE) procedure using Lichrolut EN cartridges and elution with methanol, the matrix effects were substantially reduced and the LOQs were in the range 9 to 17 µg L^?1_. The recoveries of surface water samples spiked with the 5 target neonicotinoids at two concentration levels (20 and 50 µg L^?1) were in the range 89 to 109 % and the % relative standard deviations ranged from 4.3 to 7.2 %.     

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.     

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.     

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.     

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.     

Sensitive Electrochemical Detection of Horseradish Peroxidase at Disposable Screen‐Printed Carbon Electrode

A rapid, simple and sensitive electrochemical assay of horseradish peroxidase (HRP) performed on disposable screen‐printed carbon electrode was developed. HRP activities were monitored by square‐wave voltammetric (SWV) measuring the electroactive enzymatic product in the presence of o‐aminophenol and hydrogen peroxide substrate solution. SWV analysis demonstrated a greater sensitivity and shorter analysis time than the widely used amperometric and differential‐pulsed voltammetric methods. The voltammetric characteristics of substrate and enzymatic product as well as the parameters of SWV analysis were optimized. Under optimized conditions, a linear response for HRP from 0.003 to 0.1 U/mL and a detection limit of 0.002 U/mL (1.25×10^?15 mol in 25 μL) were obtained with a good precision (RSD=8%; n=6). This rapid and sensitive HRP assay with microliter‐assay volume could be readily integrated to portable devices and point‐of‐care (POC) diagnosis applications.     

Electrochemistry and Adsorptive Stripping Voltammetric Determination of Amoxicillin on a Multiwalled Carbon Nanotubes Modified Glassy Carbon Electrode

The study of electrochemical behavior of amoxicillin (AMX), a β‐lactam antibiotic, is described on a multiwalled carbon nanotubes (MWCNTs) modified electrode by electrochemical impedance spectroscopy (EIS) and adsorptive stripping voltammetry for sensitive determination of AMX in pharmaceutical and human urine samples within a wide pH range from 2.0 to 10.0. Also, studies by Fe₂O₃ nanoparticles modified carbon paste electrode show that iron oxide impurities in the MWCNTs are not active sites for sensing of amoxicillin. Under optimized conditions, the oxidation peak has two linear dynamic ranges of 0.6–8.0 and 10.0–80.0 μM with a detection limit of 0.2 μM and a precision of <4%.     

Ionic Liquid‐Carbon Nanotube Modified Screen‐Printed Electrodes and Their Potential for Adsorptive Stripping Voltammetry

Compared with paraffin oil, the use of ionic liquids as a binder in carbon paste type electrodes was shown to greatly enhance the accumulation of analytes, as illustrated with 17α‐ethynylestradiol as a model. The ionic “liquid” n‐octyl‐pyridinium hexafluorophosphate [C₈py][PF₆] was most efficient among several ionic liquids investigated. Such preconcentration allowed a [C₈py][PF₆]‐multiwalled carbon nanotubes (MWCNTs) (95 : 5 w/w) composite electrode to be useful for adsorptive stripping voltammetry. Screen‐printed electrodes modified with [C₈py][PF₆]‐MWCNTs were developed and were able to achieve high sensitivity during adsorptive stripping voltammetric measurements under optimised conditions.     

Bismuth‐Coated Screen‐Printed Microband Electrodes for On‐Field Labile Cadmium Determination

Performances of a screen‐printed microband electrode prepared by ex situ bismuth deposition are reported. According to the low bismuth toxicity, this electrode represents an environmentally friendly alternative to mercury modified sensors, particularly for on‐field measurements. The electrochemical behaviour of the microband electrode has been studied and is in agreement with microelectrode theory before and after bismuth modification. Sensitive cadmium analysis achieved in nondeaerated and unstirred solutions leads to a detection limit of 1.3 μg L^?1 using SWASV for 120 s deposition time. This sensor has been successfully applied to a nontreated river water sample.     

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.     

Electroanalytical Sensor Based on Unmodified Screen‐Printed Carbon Electrode for the Determination of Levo‐Thyroxine

The electrochemical behaviour of thyroxine (T₄) is analysed using the disposable screen‐printed carbon electrode (SPCE) in the neutral phosphate buffer solution with cyclic voltammetric technique. The Differential Pulse Voltammetry and Chronoamperometry were employed for sensing of T₄. The lowest detection limit of 3 nM was obtained from the differential pulse voltammetric method without preconditioning. The Density Functional Theoretical study of T₄ was performed to elucidate the mechanism of oxidation. The analysis of the commercial pharmaceutical samples indicates the validity of the proposed method.     

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 %).     

Lead Sensor Using Gold Nanostructured Screen‐Printed Carbon Electrodes as Transducers

Gold nanostructured screen‐printed carbon electrodes are demonstrated to be suitable transducers for the determination of lead using square‐wave voltammetry. Reproducible gold nanostructures have been obtained by direct electrochemical deposition. A calibration plot from 2.5 to 250 μg/L was obtained in acidic solutions of Pb(II) with a reproducibility of 4% (n=10). The detection limit was 0.09 μg/L of lead. The method is then applied to perform a blood lead analysis by adjusting square‐wave parameters in capillary or venous blood with a minimum sample pretreatment and excellent accuracy and reproducibility.     

Screen‐Printed Disposable Sensors Modified with Bismuth Precursors for Rapid Voltammetric Determination of 3 Ecotoxic Nitrophenols

This work reports the application of screen‐printed electrodes bulk‐modified with bismuth precursors to the voltammetric determination of 2‐nitrophenol (2‐NP), 4‐nitrophenol (4‐NP) and 2,4‐dinitrophenol (2,4‐DNP) in water samples. A bismuth film was formed at the electrode surface via in situ reduction of the precursor compound contained in the electrode matrix by cathodic polarization at ?1.20 V. The formation of bismuth layer at the precursor‐modified electrodes was assessed by cyclic voltammetric (CV) at different pH values and by optical techniques. The target nitrophenols were voltammetrically determined by recording their reduction peaks in the differential pulse (DP) mode. The composition and content of the precursor compounds in the printed ink and the effect of the pH of the supporting electrolyte on the DP reduction currents of the 3 target nitrophenols were studied. The limits of quantification (LOQs) in three water matrices (distilled water, tap water and surface water) were in the range 1.1–2.2 µmol L^?1_. Using a simple solid‐phase extraction (SPE) procedure with Lichrolut EN cartridges and elution with methanol, a preconcentration factor of 100 was achieved; the LOQs were 0.021, 0.027 and 0.025 µmol L^?1 for 2‐NP, 4‐NP and 2,4‐DNP, respectively. The recoveries of samples spiked with the 3 target nitrophenols at two concentration levels (0.04 and 0.1 µmol L^?1) were always >87 %.     

Anodic Stripping Voltammetric Determination of Aurothiomalate in Urine Using a Screen‐Printed Carbon Electrode

This work describes an electroanalytical method for determining gold(I) thiomalate, aurothiomalate, widely used for treatment of reumatoid arthiritis, using a screen‐printed carbon electrode (SPCE). Aurothiomalate (AuTM) was determined indirectly at the same electrode by accumulating it first at ?1.5 V vs. printed carbon. At this potential in the adsorbed state, the AuTM is reduced to Au(0), which is then oxidized at two steps at ?0.22 V and +0.54 V on SPCE. Using optimized conditions of 60 s deposition time, ?1.5 V (vs. printed carbon) accumulation potential, 100 mV s^?1 scan rate, linear calibration graphs can be obtained by monitoring the peak at +0.54 V for AuTM in HCl 0.1 mol L^?1 from 1.43×10^?6 to 1.55×10^?4 mol L^?1. A limit of detection obtained was 6.50×10^?7 mol L^?1, and the relative standard deviation from five measurements of 3.0×10^?5 mol L^?1 AuTM is 4.5%. The method was successfully applied for AuTM determination in human urine sample.     

Adsorptive Stripping Voltammetric Detection of Tea Polyphenols at Multiwalled Carbon Nanotubes‐Chitosan Composite Electrode

This study reports the catalytic oxidation and detection of tea polyphenols (TPs) at glassy‐carbon electrode modified with multiwalled carbon nanotubes‐chitosan (MWCNTs‐CS) film. The adsorption of TPs at the surface of the MWCNTs through π–π conjugation prevents the aggregation of nanotubes and induces a stable MWCNTs suspension in water over 30 days. Based on the adsorptive accumulation of polyphenols at MWCNTs, TPs is sensitively and selectively detected by adsorptive stripping voltammetry. The accumulation conditions and pH effect on the adsorptive stripping detection were examined. The linear range was found to be 100 to 1000 mg L^?1 with a detection limit of 10 mg L^?1 (S/N=3) for 2.5 min accumulation. Additionally, the MWCNTs‐CS electrode is easily renewed by applying positive potential to remove the adsorbed TPs. This method was successfully applied to determine TPs in commercially available teas with satisfied result compared with that of conventional spectrometric analysis.     

Electrochemical Determination of Dextromethorphan on Reduced Graphene Oxide Modified Screen‐Printed Electrode after Electromembrane Extraction

In this paper, electromembrane extraction coupled with differential pulse voltammetry (DPV) on a reduced graphene oxide modified screen‐printed carbon electrode (RGO‐SPCE) for the determination of dextromethorphan (DXM) in urine and plasma has been described. DXM migrated from 4 mL of a donor phase across a thin layer of 2‐nitrophenyl octyl ether (NPOE) immobilized in the pores of a porous hollow fiber, into a 20 µL acceptor phase (HCl) present inside the lumen of the fiber. Then, 15 µL of a 0.1 M NaOH solution was added to the acceptor phase and the mixture was analyzed using DPV.