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.     

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.     

Screen‐Printed Electrodes for Amperometric Determination of Iodide

An amperometric method for the determination of iodide ions has been developed using disposable, screen‐printed electrodes. The used sensors have a gold, graphite and platinum working electrodes with an area of about 7 mm². Calibration curves exhibit a linear relationship between the electrode response and the iodide concentration up to 3.00 mM. The correlation coefficients for all calibration curves varied from 0.988 to 0.998. The relative standard deviations were equal to or less than 5.26 % (n=5). The lowest iodide concentration measured was 100 µM.     

Electrochemical Analysis of Acrylamide Using Screen‐Printed Carboxylated Single‐Walled Carbon Nanotube Electrodes

Acrylamide (AA) was electrochemically detected and quantified by means of its voltammetric response on carboxylic modified Single‐Walled Carbon Nanotube Screen Printed Electrodes (COOH‐SWCNT‐SPEs). The electroreduction signal of AA was proportional to AA concentration at low values (below 300 µM) and the observed sensitivity was explained in terms of AA adsorption on the COOH‐SWCNT‐SPEs that was demonstrated using the electrochemical response of [Fe(CN)₆]^3? and [Fe(CN)₆]^4? and Raman spectroscopy experiments. In order to test the suggested analytic approach (LOD of 0.03 µM, LOQ of 0.04 µM), detection and quantification of AA in fried potatoes was carried out using the proposed electrochemical method and HPLC. Both techniques showed similar contents of AA.     

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.     

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.     

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 %.     

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.     

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.     

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.     

Simultaneous Determination of Cr(III) and Cr(VI) by Differential Pulse Voltammetry Using Modified Screen‐Printed Carbon Electrodes in Array Mode

A new procedure for the speciation of chromium by means of differential pulse voltammetry using screen‐printed carbon electrodes (SPCEs) has been proposed. Two different modified carbon working, a Ag/AgCl reference and a carbon counter screen‐printed electrodes have been connected in array mode for the simultaneous determination of Cr(III) and Cr(VI). Mercury films or gold nanoparticles have been ground onto the SPCEs in order to improve their selectivity to each chromium species. The quantification of the peak currents observed at ?1.25 V in Hg‐SPCE and ?0.1 V in AuNPs‐SPCE were carried out. The method has been applied to the speciation of chromium in waste water from a tannery factory.     

Disposable Screen‐Printed Carbon Electrodes for Dual Electrochemiluminescence/Amperometric Detection: Sequential Injection Analysis of Oxalate

This work describes the development and application of an electrochemical cell specifically designed for disposable screen printed carbon electrodes (SPCE) suitable for simultaneous electrochemiluminescence (ECL) and amperometric detection in sequential injection analysis. The flow system with facility for photomultiplier tube via a fiber optic facing the SPCE is user‐friendly and makes the detection process very easy to operate. Instead of the need to constant deliver the chemiluminescence (CL) reagents to the reaction zone, sequential injection analysis allows a considerable reduction in the consumption of the sample and expensive CL reagents (such as Ru(bpy) salts). The utility of the analyzer was demonstrated for the detection of oxalate based on the ECL reaction with Ru(bpy) . Under optimized conditions, in the presence of 100 μM Ru(bpy) , the linear ranges of peak current and ECL light intensity for oxalate distinctly varied from 10 μM to 5 mM and 0.1 μM to 100 μM, respectively. In other words, the linear detection can be covered over a four‐order range with the combination of these two signals.     

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.     

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.     

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.     

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.     

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.     

A Disposable Homemade Screen Printed Electrochemical Sensor for Vitamin B1 Determination in Multivitamin Ampoules: Potentiometric and Surface Morphology Studies

Thiamine chloride hydrochloride (TCH) is one of the B‐complex vitamins which resemble a very biologically important group of biomolecules. The first screen‐printed graphite ion‐selective sensor for the determination of TCH was prepared and characterized. The sensor is based on TCH‐tetraphenylborate as electrode material. A number of parameters such as the type of solvent mediator, weight percent of the ion‐exchanger, test solution temperature and possible interferences were extensively studied. Moreover, the surface morphology of the prepared sensor was studied using scanning electron microscopy. The sensor shows a Nernstian slope of 30.60±0.07 mV/decade, a low LOD of 5.08×10⁻⁶ mol/L and a wide applicability range of 5.96×10⁻⁶‐1.00×10⁻² mol/L. The sensing graphite ink remains usable for at least one month. Fast potentiometric response was obtained within 5 s and remains stable for at least 60 s. The sensor was applied to the analysis of TCH in pure solutions and multivitamin ampoules from the Egyptian market using the standard addition method and high recovery values of 97–102 % were obtained. Low %RSD values (0.27‐1.30) indicate high precision of the proposed sensor. Our sensor provides the advantages of disposability, simple preparation procedures, sensitivity and easy storage and transportation.     

Determination of Free Metal Ion Concentrations Using Screen‐Printed Electrodes and AGNES with the Charge as Response Function

AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) has been implemented with screen‐printed electrodes (SPE) for the determination of the free concentration of Zn²⁺, Cd²⁺ and Pb²⁺. For SPE, the stripped charge is a suitable response function which does not require the second stage of AGNES to be under diffusion limited conditions. This property can be used in the avoiding of the interference of Pb on [Cd²⁺] determination. The proportionality factor between stripped charge and concentration of amalgamated metal depends on the volume of mercury and opens the way to a future calibrationless strategy. Zn and Cd complexation with oxalate at various pH‐values confirms the suitability of the developed methodology, which compares favourable with the standard one based on the Hanging Mercury Drop Electrode.     

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.