Electrochemical Characterization of Carbon Solidlike Paste Electrode Assembled Using Different Carbon Nanoparticles

Solid like carbon paste electrodes (SCPEs) are built using different carbon materials namely carbon black N110, N220, N375, N772 and acetylene black. The electrochemical behavior of these electrodes and the influence of carbon black/paraffin ratio were studied and the results were discussed and compared to other electrodes prepared with graphite, mesoporous carbon and nanopowder carbon. Cyclic voltammetry, amperometry and electrochemical impedance spectroscopy were employed for their electrochemical and analytical characterizations. Amperometric measurements using N110, N220, N375 SCPEs with solid paraffin, showed a linear response of benzoquinone concentration with a detection limit of 75, 32 and 171 nM respectively.     

Carbon Black‐Modified Electrodes as Sensitive Tools for the Electrochemical Detection of Nitrite and Nitrate

Both screen‐printed electrodes modified with a dispersion of carbon black (CB) and solid paste electrodes prepared using a nanostructured CB were developed and characterized. Indeed, increasing the peak currents and/or their shifting to negative potentials were observed, exhibiting efficient electrocatalytic activity towards nitrite oxidation with high sensitivity and low detection limit. Solid carbon paste electrodes (SCPEs) and solid carbon black paste electrodes (SCBPEs) were challenged in amperometric mode with nitrite since detection limit reached is 65 and 5 nM respectively. Nitrate was first reduced to nitrite in reductor column, then detected on SCBPEs. Nitrate and nitrite were determined in real samples.     

Flow and batch systems for copper(II) potentiometric sensing

A new carbon paste electrode modified with tetramethyl thiuram disulfide is prepared to use as copper potentiometric sensor in batch and flow analysis. The influence of pH and carbon paste composition on the potentiometric response is studied. The principal parameters of the flow system are optimized and the detection limits and the selectivity coefficients of the potentiometric sensor are calculated for static and flow mode. In both cases, the sensor shows high selectivity to copper ions but in flow analysis this selectivity is higher. The obtained detection limits are 4.6 × 10⁻⁸ M for batch measurements and 2.0 × 10⁻⁷ M for on-line analysis. The potentiometric sensor is applied to copper(II) determination in real samples in static and flow measurements. In both analysis modes, successful results are obtained.     

All-plastic, disposable, low detection limit ion-selective electrodes

A novel concept for all-plastic and all-solid-state ion-selective electrodes (ISEs) is introduced. Planar, flexible ion-selective electrodes, comprising only polymeric materials, with no internal solution, were obtained. The cast conducting polymer layer (obtained from aqueous suspension) was covered with a solvent polymeric based membrane to obtain a planar all-plastic sensor. The conducting polymer layer served both as electrical contact and as ion-to-electron transducer. To illustrate this concept, the conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) ions (PEDOT-PSS, Baytron P) was chosen. Due to interaction, analyte cations-poly(4-styrenesulfonate) anions, an extended linear range of potentiometric responses was obtained, with lowered detection limit.As example, Ca²⁺-selective and K⁺-selective all-plastic electrodes were fabricated and yielded with high selectivity, near Nernstian slopes and fast responses. The detection limits obtained for Ca²⁺- and K⁺-selective sensors were 5 × 10⁻⁹ M CaCl₂ and 4.4 × 10⁻⁷ M KCl, respectively.The possibilities of modifying the conducting polymer-phase composition is highlighted. This method is extremely useful to tune the desired type of responses, and cannot be directly applied for electrochemically deposited conducting polymers.     

Room Temperature Ionic Liquids (RTILs) and Multiwalled Carbon Nanotubes (MWCNTs) as Modifiers for Improvement of Carbon Paste Ion Selective Electrode Response; A Comparison Study with PVC Membrane

Room temperature ionic liquids (RTILs), 1‐n‐butyl‐3‐methylimidazolium tetrafluoroborate, [bmim]BF₄, and multiwalled carbon nanotubes (MWCNTs) were used for improvement of a praseodymium carbon paste ion selective sensor response. [bmim]BF₄ can be a better binder than mineral oils. MWCNTs have a good conductivity which helps the transduction of the signal in carbon paste electrode. The characteristics of these electrodes as potentiometric sensors were evaluated and compared with PVC membrane sensor. The results indicate that potentiometric sensor constructed with ionic liquid shows an increase in performance in terms of Nernstian slope, selectivity, response time, and response stability compared to Pr(III) PVC membrane sensor.     

Construction of novel simple phosphate screen-printed and carbon paste ion-selective electrodes

The construction and performance characteristics of different phosphate ion-selective electrodes are described. Three types of electrodes are demonstrated, namely screen-printed, carbon paste and the conventional PVC membrane electrodes. The cited electrodes are based on bisthiourea ionophores and show a considerable selectivity towards hydrogenphosphate with Nernstian slopes depending on the type of the electrode and the ionophore used. Matrix compositions of each electrode are optimised on the basis of effects of type and concentration of the ionophore as well as influence of the selected plasticizers. The screen-printed electrodes work satisfactorily in the concentration range 10⁻⁵ to 10⁻² mol L⁻¹ with anionic Nernstian compliance (32.8 mV/decade activity) and detection limit 4.0 × 10⁻⁶ mol L⁻¹. The screen-printed electrodes show fast response time of about 2.2 s and exhibit adequate shelf-life (4 months). The fabricated electrodes can be also successfully used in the potentiometric titration of HPO₄²⁻ with Ba²⁺.     

Novel potentiometric sensors for pyrilamine maleate

The fabrication and electrochemical response characteristics of four novel potentiometric sensors for determination of pyrilamine maleate (PyraH) were described. The sensors include polymeric membrane electrodes (PME₁, PME₂) and carbon paste electrodes (CPE₁, CPE₂). The fabricated sensors were based on the ion-pair of pyrilamine with sodium tetraphenylborate (NaTPB) and ammonium reineckate (NH₄RN) using dibutyl phthalate (DBP) as plasticizing solvent. The sensors showed linear, stable and near-Nernstian slopes of 56.4 ± 0.4, 54.2 ± 0.2, 58.8 ± 0.3 and 57.9 ± 0.4 mV decade^?1 at 25 ± 0.1 °C and detection limits of 2.0 × 10^?5, 1.8 × 10^?5, 1.0 × 10^?5 and 9.5 × 10^?6 mol L^?1 for PME₁, PME₂, CPE₁ and CPE₂ sensors, respectively. The response time was less than 10 and 8 s for polymeric membrane and carbon paste sensors. The proposed sensors displayed good selectivity for pyrilamine with respect to a number of common inorganic and organic species. The thermal temperature coefficients of the investigated sensors were 0.9508, 0.7012, 0.9450 and 0.6497 mV °C^?1. Modified carbon paste sensors showed lower detection limits, higher thermal stability and faster response time than those of polymeric membrane sensors. The proposed sensors displayed useful analytical characteristics for determination of pyrilamine in pharmaceutical preparation and biological fluids (Human urine and plasma).     

Comparative studies of mercapto thiadiazoles self-assembled on gold nanoparticle as ionophores for Cu(II) carbon paste sensors

Comparative studies of the potentiometric behavior of three mercapto compounds [2-((5-mercapto-1,3,4-thiadiazol-2-ylimino)methyl)phenol] (MTMP), [5-(2-methoxy benzylidene amino)-1,3,4-thiadiazole-2-thiol] (MBYT) and [5-(pyridin-2-ylmethyleneamino)-1,3,4-thiadiazole-2-thiol] (PYTT) self-assembled on gold nanoparticles (GNPs) as ionophores in carbon paste electrodes (CPEs) have been made. These mercapto thiadiazole compounds were self-assembled onto gold nanoparticles and then incorporated within carbon paste electrode. The self-assembled ionophores exhibit a high selectivity for copper ion (Cu²⁺), in which the sulfur and nitrogen atoms in their structure play a role as the effective coordination donor site for the copper ion. These carbon paste electrodes were applied as indicator electrodes for potentiometric determination of copper ions. The sensor based on PYTT exhibits the working concentration range of 4.0 × 10⁻⁹ to 7.0 × 10⁻² M and a Nernstian slope of 28.7 ± 0.3 mV decade⁻¹ of copper activity. The detection limit of electrode was 1.0 × 10⁻⁹ M and potential response was pH independent across the range of 3.0-6.5. It exhibited a quick response time of <5 s and could be used for a period of 45 days. The ion selectivity of this electrode for Cu²⁺ was over 10⁴ times that for other metal cations. The application of prepared sensors has been demonstrated for the determination of copper ions in spiked water and natural water samples.     

Ionic Liquids Modify the Performance of Carbon Based Potentiometric Sensors

A new type of potentiometric sensor based on a recently constructed carbon ionic liquid electrode (CILE) is described. Two kinds of ionic liquids, i.e., N‐octylpyridinium hexafluorophosphate (OPFP) and 1‐butyl‐3‐methylimidazoluim hexafluorophosphate (BMFP) were tested as binder for construction of the carbon composite electrode. The characteristics of these electrodes as potentiometric sensors were evaluated and compared with those of the traditional carbon paste electrode (CPE). The results indicate that potentiometric sensors constructed with ionic liquid show an increase in performance in terms of Nernstian slope, selectivity, response time, and response stability compared to CPE.     

Multivariate optimisation of electrochemically pre-treated electrodes used in a voltammetric electronic tongue

The use of experimental design as a tool to optimise electrochemically cleaned electrodes applied in a voltammetric electronic tongue is described. A simple and quick activation of electrode surfaces is essential for this type of device, especially for on-line applications in industrial processes. The electronic tongue consisted of four metal electrodes, e.g. Au, Ir, Pt, and Rh in a three-electrode configuration. Current was measured as a function of large potential pulses of decreasing amplitude applied to each electrode. Preliminary results showed that electrochemical cleaning activated the electrode surfaces to similar extent as polishing. Settings of potential and time for each electrode was determined with experimental design in a solution containing 1.0 mM K₄[Fe(CN)₆] in 0.1 M phosphate buffer (pH 6.8). Electrode surfaces were deactivated in-between measurements in a complex liquid, like tea. Optimal settings for potential and time in the electrochemical cleaning procedure at each electrode were chosen at recoveries of 100% (compared to polished electrodes). The recoveries were larger than 100% when too large potentials and times were applied. This could be explained by the fact that the electrode areas increased and therefore also the current responses. Principal component analysis (PCA) was used to investigate the stability of the electrode settings at 100% recoveries. No obvious trends of drift in the signals were found.     

Anodic stripping voltammetry at a new type of disposable bismuth-plated carbon paste mini-electrodes

A new type of disposable carbon paste mini-electrodes (CPmEs), with dimensions in the 50-300 μm range, have been fabricated by heat-shrinking the end-tip of plastic micropipette tips and filling them with carbon paste. The CPmEs have been characterized by microscopic and electrochemical means and tested as substrates for in situ plated Bi film electrodes (BiF-CPmEs), used in the determination of heavy metals by square wave anodic stripping voltammetry (SWASV). It was found that this new class of CPmEs combines the advantages of carbon paste electrodes (readily renewable surface and high surface area) with those of near-microelectrode behaviour (no stirring or electrolyte excess needed). During SWASV experiments in unstirred Pb(II) and Cd(II) solutions well-shaped stripping peaks were obtained whose height varied linearly with analyte concentration in the wide 1 × 10⁻⁸ to 10⁻⁶ M range, both in acetate buffer and unbuffered solutions. Under optimal conditions detection limits of 8 × 10⁻¹⁰ and 1.3 × 10⁻⁹ M were achieved for Pb(II) and Cd(II), respectively and in a trial application, these metal ions have been determined in a spiked tap water sample using a BiF-CPmE.     

Comparison of different carbon nanostructures influence on potentiometric performance of carbon paste electrode

Recently, different carbon nanomaterials were introduced for construction of electrochemical sensors. In this study, the influence of carbon nanomaterial on performance of carbon paste potentiometric electrode was investigated. In this manner, different kinds of carbon nanomaterial, i.e., graphene, graphene oxide and carbon nanotube (CNT) were used as a conduction phase in carbon paste electrode. Then, potentiometric characteristics of the corresponding paste electrodes such as calibration slope, linear range, detection limit, response time and stability were compared with each other. The results appeared comprehensive findings about the role of electrode’s content in electrochemical performance.     

Development and characterization of ion selective electrode for the assay of antimony

The construction and general performance characteristics of two novel potentiometric carbon paste electrodes (CPE) responsive to antimony are described. These sensors are based on the use of the ion associate complexes of tetraiodoantimonate (TIA) anion with cetylpyridinium (CP) and triphenyl tetrazolium (TPT) counter cations as ion exchange site in a carbon paste matrix. The two sensors exhibits fast, stable and near-Nernstian for the mono charged TIA anion over the concentration range 1 × 10⁻³ to 10⁻⁶ M at 25 °C in the pH range 4-10 with anionic slope of 58.0 ± 0.5 and 55.0 ± 0.7 per concentration decade for TIA-CP and TIA-TPT, respectively. The lower detection limits are 4 and 5 × 10⁻⁶ M and response time are 20 and 30 s in the same order of both electrodes. Selectivity coefficients for antimony relative to a number of different cations and anions were investigated. There is negligible interference from many inorganic cation and anion except for Hg²⁺, Cd²⁺, and Bi³⁺; however, their effect were eliminated by EDTA. The determination of 1.0-120.0 μg/ml of antimony in aqueous solutions shows an average recovery of 99.0 and 97.5% with relative standard deviation of 2.0% for both electrodes at 40 μg/ml. The determination of antimony in wastewater and some antibilharzial compounds using the proposed electrodes gave results that compare favorably with those obtained by the atomic absorption spectrometric method. Precipitation titrations involving cetylpyridinium chloride as titrant are monitored with both electrodes with inflection point of 180 and 100 mV for TIA-CP and TIA-TPT, respectively.     

An electronic tongue for gliadins semi-quantitative detection in foodstuffs

An all-solid-state potentiometric electronic tongue with 36 polymeric membranes has been used for the first time to detect gliadins, which are primarily responsible for gluten intolerance in people suffering from celiac disease. A linear discriminant model, based on the signals of 11 polymeric membranes, selected from the 36 above using a stepwise procedure, was used to semi-quantitatively classify samples of a “Gluten-free” foodstuff (baby milked flour), previously contaminated with known amounts of gliadins (<10, 20-50 or >50 mg/kg), as “Gluten-free”, “Low-Gluten content” or “Gluten-containing”. For this food matrix, the device had sensitivity towards gliadins of 1-2 mg/kg and overall sensitivity and specificity of 77% and 78%, respectively. Moreover, the device never identified an ethanolic extract containing gliadins as “Gluten-free”. Finally, the system also allowed distinguishing “Gluten-free” and “Gluten-containing” foodstuffs (15 foods, including breads, flours, baby milked flours, cookies and breakfast cereals) with an overall sensitivity and specificity greater than 83%, using the signals of only 4 selected polymeric membranes (selected using a stepwise procedure). Since only one “Gluten-containing” foodstuff was misclassified as “Gluten-free”, the device could be used as a preliminary tool for quality control of foods for celiac patients.     

Novel Ag ion-selective electrodes based on two new mixed azathioether crowns containing a 1,10-phenanthroline sub-unit

Novel polymeric membrane (PME) and coated graphite (CGE) silver-selective electrodes based on two recently synthesized mixed azathioether crowns containing a 1,10-phenanthroline sub-unit were prepared. The electrodes reveal a Nernstian behavior over quite wide Ag⁺ ion concentration ranges with a very low limits of detection (LOD) (i.e. down to 1.0×10⁻⁸ M for CGEs and 8.0×10⁻⁷ M for PMEs). The potentiometric responses are independent of the pH of the test solution in the pH range 3.0-7.0. The electrodes possess advantages of low resistance, very fast response time, relatively long lifetimes and, especially, good selectivities relative to a wide variety of other cations. The electrodes were used, as indicator electrodes, in the potentiometric titration of silver ion and in the determination of Ag⁺ in waste water, photographic emulsion and radiographic and photographic films.     

All-solid-state potentiometric sensors for ascorbic acid by using a screen-printed compatible solid contact

The development of all-solid-state potentiometric ion selective electrodes for monitoring of ascorbic acid, by using a screen-printed compatible solid contact is described. The applied methodology is based on the use of PVC membrane modified with some firstly-tested ionophores (triphenyltin(IV)chloride, triphenyltin(IV)hydroxide and palmitoyl-l-ascorbic acid) and a novel one synthesized in our laboratory (dibutyltin(IV) diascorbate). Synthesis protocol and some preliminary identification studies are given. A conductive graphite-based polymer thick film ink was used as an internal solid contact between the graphite electrode and the PVC membrane. The presence and the nature of the solid contact (plain or doped with lanthanum 2,6-dichlorophenolindophenol (DCPI)) seem to enhance the analytical performance of the electrodes in terms of sensitivity, dynamic range, and response time. The analytical performance of the constructed electrodes was evaluated with potentiometry, constant-current chronopotentiometry and electrochemical impedance spectroscopy (EIS). The interference effect of various compounds was also tested. The potential response of the optimized Ph₃SnCl-based electrode was linear against ascorbic acid concentration range 0.005-5.0 mM. The applicability of the proposed sensors in real samples was also tested. The detection limit was 0.002 mM ascorbic acid (50 mM phosphate, pH 5 in 50 mM KCl). The slope of the electrodes was super-Nernstian and pH dependent, indicating a mechanism involving a combination of charge transfer and ion exchange processes. Fabrication of screen-printed ascorbate ISEs has also been demonstrated.     

Enantioselective,Potentiometric Carbon Paste Electrodes Based on C60 Derivatives as Chiral Selectors for the Enantioanalysis of S‐Clenbuterol

Abstract

Three enantioselective, potentiometric carbon paste electrodes (EPCPEs) based on carbon paste impregnated with (1,2‐methanofullerene C60)‐61‐carboxylic acid (I), diethyl (1,2‐methanofullerene C60)‐61‐61‐dicarboxylate (II), and tert‐butyl (1,2‐methanofullerene C60)‐61‐carboxylic acid (III) are reported. Response characteristics showed that the proposed electrodes could be reliably used in the assay of S‐clenbuterol raw material and in serum samples. The surfaces of the electrodes are stable and easily renewable by simply polishing on an alumina paper.     

Hybrid Electronic Tongue as a Tool for the Monitoring of Wine Fermentation and Storage Process

Hybrid electronic tongue based on potentiometric and voltammetric sensors was applied for the monitoring of wine production process. The sensor array formed by miniaturized ion‐selective electrodes and glassy carbon electrodes provided the analysis of the progress and correctness of wine fermentation and storage process, detection of the presence of disturbing factors and evaluation of the quality of final product. The efficiency of the proposed approach was compared with the monitoring of wine production carried out using standard reference methods. The results indicated that hybrid electronic tongue could be used as simple and reliable analytical tool dedicated to qualitative and quantitative assessment of wine production.     

All-solid-state carbonate-selective electrode based on a molecular tweezer-type neutral carrier with solvent-soluble conducting polymer solid contact

Carbonate-selective membranes were prepared by incorporating a molecular tweezer-type carbonate-selective neutral carrier [N,N-dioctyl-3alpha,12alpha-bis(4-trifluoroacetylbenzyloxy)-5beta-cholan-24-amide] into a room temperature vulcanizing-type silicone rubber (3140 RTV-SR) matrix, and deposited on the planar-type electrodes (Pt containing Ag/AgCl electrodes formed on a ceramic plate) with and without an intermediary conducting polymer layer. Two types of solvent-soluble conducting polymers [poly(1-hexyl-3,4-dimethyl-2,5-pyrrolylene) or poly(3-octylthiophene-2,5-diyl)] have been examined as the solid contact material. Potentiometric properties of the resultant all-solid-state electrodes were evaluated in terms of their carbonate selectivity, response slope, potential stability and reproducibility. The sensitivity and carbonate selectivity of the SR membrane-based all-solid-state electrodes with conducting polymer solid contact were comparable to those of conventional electrodes. Experimental results also showed that the intermediary conducting polymer layer used in the all-solid-state electrodes greatly reduces the interference from dissolved oxygen.