Lead(II) Potentiometric Sensor Based on 1,4,8,11‐Tetrathiacyclotetradecane Neutral Carrier and Lipophilic Additives

A potentiometric sensor for lead(II) ions based on the use of 1,4,8,11‐tetrathiacyclotetradecane (TTCTD) as a neutral ionophore and potassium tetrakis‐(p‐chlorophenyl)borate as a lipophilic additive in plasticized PVC membranes is developed. The sensor exhibits linear potentiometric response towards lead(II) ions over the concentration range of 1.0×10^?5–1.0×10^?2 mol L^?1 with a Nernstian slope of 29.9 mV decade^?1 and a lower limit of detection of 2.2×10^?6 mol L^?1 Pb(II) ions over the pH range of 3–6.5. Sensor membrane without a lipophilic additive displays poor response. The sensor shows high selectivity for Pb(II) over a wide variety of alkali, alkaline earth and transition metal ions. The sensor shows long life span, high reproducibility, fast response and long term stability. Validation of the method by measuring the lower limit of detection, lower limit of linear range, accuracy, precision and sensitivity reveals good performance characteristics of the proposed sensor. The developed sensor is successfully applied to direct determination of lead(II) in real samples. The sensor is also used as an indicator electrode for the potentiometric titration of Pb(II) with EDTA and potassium chromate. The results obtained agree fairly well with data obtained by AAS.     

New Macrocyclic Diamides as Neutral Ionophores for Highly Selective and Sensitive PVC‐Membrane Electrodes for Be2+ Ion

Five recently synthesized macrocyclic diamides were investigated to characterize their ability as beryllium ion carriers in potentiometric PVC‐membrane electrodes. The electrodes based on 1,15‐diaza‐3,4;12,13‐dibenzo‐5,8,11‐trioxabicyclo[13,2,2] heptadecane‐2,14‐dione exhibited a Nernstian response for Be²⁺ ion over wide concentration ranges (from 3.0×10^?6 to 3.0×10^?2 M for polymeric membrane electrode, PME, and from 5.0×10^?7 to 2.0×10^?2 M for coated glassy carbon electrode, CGCE) and very low detection limits (2.0 ×10^?6 M for PME and 4.0×10^?7 M for (CGCE). The electrodes possess low resistances, fast responses, satisfactory reproducibilities and, most importantly, good selectivities relative to a variety of other common cations. The potentiometric response of the electrodes is independent of pH of test solution in the pH range of 4.0–7.5. The proposed sensors were used to determine beryllium ion in water samples.     

Square Wave‐Anodic Stripping Voltammetric Determination of Copper at a Bismuth Film/Glassy Carbon Electrode Using 3‐[(2‐Mercapto‐Vinyl)‐Hydrazono]‐ 1,3‐Dihydro‐Indol‐2‐One

This study reports a highly sensitive electrochemical sensor based on Bi film modified glassy carbon electrode (BiF/GCE) for total determination and speciation trace concentrations of copper(II) ions in environmental water samples. Square wave‐adsorptive anodic stripping voltammetric (SW‐ASV) experiment was performed for monitoring selective accumulation of copper(II) with reagent 3‐[(2‐mercapto‐vinyl)‐hydrazono]‐1,3‐dihydro‐indol‐2‐one (MHDI) at pH 9–10. The mechanism of the electrode reaction of Cu²⁺‐MHDI complex was safely assigned. The sensor exhibited a wide linear range (3.22×10⁻⁹–2.0×10⁻⁷ mol L⁻¹) with lower limits of detection (LOD) and quantitation (LOQ) of 9.6×1⁻¹⁰ and 3.22×10⁻⁹ mol L⁻¹, respectively (R²=0.9993). The proposed sensor exhibited interference from active metal ions e. g. Cd, Hg. The performance of the proposed method was compared successfully with most of the reported methods and comparable efficiencies were obtained. The analytical utility of the proposed SW‐ASV method has been successfully validated for trace analysis of copper(II) in environmental water samples. The method offers a precise, accurate approach with good reproducibility, robustness, ruggedness, and cost effectiveness.     

Application of 2‐(benzyliminomethyl)‐6‐methoxy‐4‐(4‐methoxyphenyl‐azo)phenol in construction of ion‐selective PVC membrane electrode for determination of copper (II) in mineral water sample

The potentiometric characteristics of a new Cu²⁺‐selective electrode based on 2‐(benzyliminomethyl)‐6‐methoxy‐4‐(4‐methoxyphenyl‐azo) phenol as an efficient ionophore has been evaluated. The effects of influential parameters on the potentiometric responses such as the amount of plasticizer, the amount of ionophore, pH of the sample solution, and the effect of coexisting ions on the electrode signal were subsequently investigated . The selectivity of the electrode was assessed by calculating the selectivity coefficients using the matched potential method. The optimum ratio of the amount of materials required for the preparation of the electrode was found to be 1.7: 32.1: 64.2: 2.0 corresponding to carboxylated PVC, dimethyl sebacate as solvent mediators, potassium tetrakis (p‐chlorophenyl) borate as the anion localizing agent, and ionophore, respectively. The electrode had a fast response (7s) as well as a satisfactory Nernstian slope (29.26±0.91 mV/decade) to Cu²⁺ over a wide concentration range of 2.0×10^?6‐ 5.0×10^?2 M with a low detection limit of 5.9×10^?7 M. The developed sensor was successfully used for the potentiometric titration of Cu²⁺ ion with EDTA and subsequently, efficient determination of this metal ion in a mineral water sample was performed.     

Construction and Performance Characterization of Ion‐Selective Electrodes for Potentiometric Determination of Paroxetine Hydrochloride in Pharmaceutical Preparations and Biological Fluids

Three types of ion‐selective electrodes: PVC membrane, modified carbon paste (CPE), and coated graphite electrodes (CGE) have been constructed for determining paroxetine hydrochloride (Prx). The electrodes are based on the ion pair of paroxetine with sodium tetraphenylborate (NaTPB) using dibutyl phthalate as plasticizing solvent. Fast, stable and potentiometric response was obtained over the concentration range of 1.1×10^?5–1×10^?2 mol L^?1 with low detection limit of 6.9×10^?6 mol L^?1 and slope of a 56.7±0.3mV decade^?1 for PVC membrane electrode, the concentration range of 2×10^?5–1×10^?2 mol L^?1 with low detection limit of 1.2×10^?5 mol L^?1 and slope of a 57.7±0.6 mV decade^?1 for CPE, and the concentration range of 2×10^?5–1×10^?2 mol L^?1 with low detection limit of 8.9×10^?6 mol L^?1 and slope of a 56.1±0.1 mV decade^?1 for CGE. The proposed electrodes display good selectivity for paroxetine with respect to a number of common inorganic and organic species. The electrodes were successfully applied to the potentiometric determination of paroxetine hydrochloride in its pure state, its pharmaceutical preparation, human urine and plasma.     

Potentiometric Quantification of the Benzoate Ion in Nonalcoholic Beverages Using a Solid Electrode Modified with a Polypyrrole‐Based Selective Membrane

This work presents the results obtained on the construction of a potentiometric ion‐selective electrode based on a polypyrrole (PPy) selective membrane to quantify the benzoate ion in nonalcoholic beverages. The electrode modification with benzoate (Benz^?1) ion doped‐Ppy was carried out under an imposed potential, while the electrosynthesis optimization was undertaken using the modified Simplex method, such that the film’s sensitivity was maximized toward the benzoate ion. The maximum sensitivity recorded was ?52.02±1.55 mV/decade [Benz^?1] using a graphite powder‐araldite resin composite electrode. During the modified electrode’s characterization it was found out that the response and drift were relatively short, namely 2 min and 0.4 mV min^?1 respectively, within the 7 to 9 pH range, exhibiting a detection limit of 7×10^?4 mol L^?1 and a quantification range of 3×10^?3 at 10^?1 mol L^?1. Selectivity coefficients were evaluated with the Matched Potential Method obtaining in all cases values much less than 1. The benzoate concentration in commercially available juices and sweetened beverages was evaluated comparing the results obtained with the proposed ion‐selective electrode and those of HPLC, the usually accepted technique. A statistical analysis of the results led to the conclusion that there exists no meaningful difference between the results obtained with both techniques, which shows the usefulness of the ion‐selective electrode to proceed with the quantification in real samples.     

New Copper(II) Ion-Selective Membrane Electrode Based on Erythromycin Ethyl Succinate as a Neutral Ionophore

Abstract

The potentiometric response characteristics of a new copper(II) ion-selective PVC membrane electrode based on erythromycin ethyl succinate (EES) as ionophore were investigated. The electrode exhibited a Nernstian response to Cu²⁺ ions over the activity range of 1.5 × 10^?2 to 2.0 × 10^?6 mol L^?1 with a limit of detection of 6.3 × 10^?7 mol L^?1. Stable potentials were obtained in the pH range of 5.5–6.5. The potentiometric selectivity coefficients were calculated by using fixed interference method and revealed no important interferences except for Ag⁺. This electrode was successfully applied as an indicator electrode in determination of copper ions in real water samples.     

Electrochemical Behaviors of Adenosine‐5′‐triphosphate on Molecular Wire Modified Carbon Paste Electrode and Its Sensitive Detection

A new electrochemical method was proposed for the determination of adenosine‐5′‐triphosphate (ATP) based on the electrooxidation at a molecular wire (MW) modified carbon paste electrode (CPE), which was fabricated with diphenylacetylene (DPA) as the binder. A single well‐defined irreversible oxidation peak of ATP appeared on MW‐CPE with adsorption‐controlled process and enhanced electrochemical response in a pH 3.0 Britton‐Robinson buffer solution, which was due to the presence of high conductive DPA in the electrode. The electrochemical parameters of ATP were calculated with the electron transfer coefficient (α) as 0.54, the electron transfer number (n) as 1.9, the apparent heterogeneous electron transfer rate constant (k_s) as 2.67 × 10^?5 s^?1 and the surface coverage (Γ_T) as 4.15 × 10^?10 mol cm^?2. Under the selected conditions the oxidation peak current was proportional to ATP concentration in the range from 1.0 × 10^?7 mol L^?1 to 2.0 × 10^?3 mol L^?1 with the detection limit as 1.28 × 10^?8 mol L^?1 (3σ) by sensitive differential pulse voltammetry. The proposed method showed good selectivity without the interferences of coexisting substances and was successful applied to the ATP injection samples detection.     

Highly Selective and Sensitive Copper(II) Membrane Sensors Based on 6‐Methyl‐4‐(1‐phenylmethylidene)amino‐3‐thioxo‐1,2,4‐triazin‐5‐one as a New Neutral Ionophore

A new Cu(II) ion‐selective PVC membrane sensor based on 6‐methyl‐4‐(1‐phenylmethylidene)amino‐3‐thioxo‐1,2,4‐triazin‐5‐one (MATTO) as an excellent sensing material was developed. The electrode exhibits a Nernstian slope of 29.2±0.4 mV per decade over a very wide concentration range between 1.0×10^?1 and 1.0×10^?6 M, with a detection limit of 4.8×10^?7 M (30.5 ng/mL). The sensor possesses the advantages of short conditioning time, fast response time (<10 s), and especially, very good selectivity towards transition and heavy metal, and some mono, di and trivalent cations. The proposed electrode was successfully applied to the determination of copper in wastewater of copper electroplating samples and as an indicator electrode in potentiometric titration of Cu(II) ions with EDTA.     

Highly Selective PVC‐Based Membrane Electrode Based on 2,6‐Diphenylpyrylium Fluoroborate

A highly selective PVC‐membrane electrode based on 2,6‐diphenylpyrylium fluoroborate is presented. The electrode reveals a Nernstian potentiometric response for sulfate ion over a wide concentration range (5.0 × 10^?6‐1.0 × 10^?1 M). The electrode has a response time of about 10 s and can be used for at least 2 months without any divergence. The proposed sensor revealed very good selectivities for sulfate over a wide variety of common organic and inorganic anions and could be used over a wide pH range (2.5–9.5). The detection limit of the sensor is 3.0 × 10^?6 M. It was successfully applied to the direct determination of salbutamol, paramomycin tablets, and as an indicator electrode for potentiometric titration of sulfate ions with barium ions.     

Single‐Piece Solid‐Contact Pb2+‐Selective Electrodes Based on Thiophene Oligomer

A single‐piece solid‐contact Pb²⁺‐selective electrode was prepared by adding a thiophene oligomer into the ion‐selective cocktail directly. The one‐step fabrication yielded an electrode with Nernstian response spanning a wide concentration range of 10^?3–10^?8 mol L^?1, and detection limit as low as 5.6×10^?9 mol L^?1. The electrode had a quick response time of approximately 10–15 s and showed excellent selectivity over the most common univalent and divalent cations. The practical application of the proposed electrode has been tested by determining Pb²⁺ in real water samples.     

Simultaneous Determination of Pb and Cd Traces in Water Samples by Anodic Stripping Voltammetry Using a Modified GC Electrode

The determination of Pb and Cd with a Nafion‐modified glassy carbon electrode and Cu‐DPABA complex (Cu‐DPABA–NA/GCE; DPABA is methyl 3,5‐bis{bis‐[(pyridin‐2‐yl)methyl]amino}methyl‐benzoate) as an alternative electrode for anodic stripping voltammetry was described. Pb and Cd were accumulated in acetate buffer pH 4 at a potential of ?1.4 V (vs. Ag/AgCl electrode) for 120 s followed by a DPASV scan from ?1.2 to ?0.2 V. Under optimum conditions the calibration curves were linear in the range of 4.8×10^?9–5.0×10^?5 and 5.0×10^?9–5×10^?5 mol L^?1 for Pb and Cd, respectively. Detection limits were 1.8×10^?9 and 1.2×10^?9 mol L^?1 for Pb and Cd, respectively. Different parameters and conditions, such as membrane ingredients, accumulation time, potential and pH value were optimized. A study of interfering substances was also performed. A significant increase in current was achieved at the modified electrode in comparison with the bare glassy carbon electrode. The validation of the proposed method was made by Pb and Cd determination in the certified reference material Groundwater CRM 610 (BCR, Community Bureau of Reference, Brussels, Belgium). The electrode was successfully applied for determination of Pb and Cd in river water with a high content of organic contaminants without any pretreatment.     

Amino‐Containing Ultrafine Organosilica‐Nanoparticle‐Modified Au Electrode for the Determination of Cu(II) Ions

Using 3‐Aminopropyltriethoxysilane(APTES) as a single silica source, an amino‐rich ultrafine organosilica‐nanoparticle‐modified Au electrode was fabricated, following the formation of (3‐mercaptopropyl)‐trimethoxysilane (MPTS) monolayer on Au surface (MPTS/Au). With cetyltrimethylammonium bromide as an additive, APTES‐based gel particles on the electrode have a narrow particle size distribution of 4–7 nm and “crystal‐like” structure. AFM and electrochemical characterization confirmed the successful grafting of APTES nanoparticles on MPTS/Au. The APTES/MPTS/Au electrode is highly sensitive for the detection of copper(II) ions with a detection limit as low as 1.6×10^?12 mol L^?1 (S/N>3) by square wave voltammetry. The current is linear to copper(II) concentration between 1.6×10^?12 and 6.25×10^?10 mol L^?1.     

A Novel Modified Carbon Paste Electrode for Potentiometric Determination of Mercury(II) Ion

A new modified carbon paste electrode (CPE) based on a recently synthesized ligand of Ethyl‐2‐(benzoylamino)‐3‐(2‐hydroxy‐4‐methoxyphenyl)‐2‐propenoate (EBHMP) as a suitable carrier for Hg²⁺ ion was described. The electrode exhibit a super Nernstian slope of 48.5±1.0 mV per decade for Hg²⁺ ion over a wide concentration range from 3.0×10^?7–3.1×10^?2 M. The lower detection limits are 1.0×10^?7 M Hg²⁺. The electrode has a fast response time (ca. 5 s), a satisfactory reproducibility and relatively long life time. The proposed sensor shows a fairly good selectivity toward Hg²⁺ ion in comparison to other common cations. The potentiometric responses are independent of the pH of the test solution in the pH range 1.0–4.0. The proposed electrode was used as an indicator electrode in potentiometric titration of mercuric ion with standard solution of EDTA. The direct determination of mercury in spiked wastewater and an amalgam sample gave results that compare favorably with those obtained by the cold vapor atomic absorption spectrometric method.     

Ion-selective carbon paste electrode based on new tripodal ligand for determination of cadmium (II)

A new chemically modified carbon paste electrode for Cd(II) ions based on 3,5-dinitro-N-(tri-2-pyridyl methyl) benzamide (DNTPMBA) as an ionophore was prepared. The electrode exhibits a Nernstian response for Cd(II) ions over a wide concentration range (2.16 × 10^?7–1.00 × 10^?1 mol L^?1) with a slope of 30 ± 1 mV per decade. It has a response time of about 50 s and can be used for a period of 3 months with good reproducibility. Detection limit obtained in the optimal conditions was 1.82 × 10^?7 mol L^?1. The electrode was successfully used for potentiometric determination of Cd(II) in well water. The pH influence and interference of some cations were also studied.     

Simultaneous Determination of Dopamine and Ascorbic Acid Using the Nano‐Gold Self‐Assembled Glassy Carbon Electrode

Electrochemical behavior of dopamine (DA) was investigated at the gold nanoparticles self‐assembled glassy carbon electrode (GNP/LC/GCE), which was fabricated by self‐assembling gold nanoparticles on the surface of L ‐cysteine (LC) modified glassy carbon electrode (GCE) via successive cyclic voltammetry (CV). A pair of well‐defined redox peaks of DA on the GNP/LC/GCE was obtained at E_pa=0.197 V and E_pc=0.146 V, respectively. And the peak separation between DA and AA is about 0.2 V, which is enough for simultaneous determination of DA and AA. The peak currents of DA and AA were proportional with their concentrations in the range of 6.0×10^?8–8.5×10^?5 mol L^?1 and 1.0×10^?6–2.5×10^?3 mol L^?1, with the detection limit of 2.0×10^?8 mol L^?1 and 3.0×10^?7 mol L^?1 (S/N=3), respectively. The modified electrode exhibits an excellent reproducibility, sensibility and stability for simultaneous determination of DA and AA in human serum with satisfactory result.     

Voltammetric Determination of 3‐Nitrofluoranthene and 3‐Aminofluoranthene at Boron Doped Diamond Thin‐Film Electrode

The voltammetric behavior of 3‐nitrofluoranthene and 3‐aminofluoranthene was investigated in mixed methanol‐water solutions by differential pulse voltammetry (DPV) at boron doped diamond thin‐film electrode (BDDE). Optimum conditions have been found for determination of 3‐nitrofluoranthene in the concentration range of 2×10^?8–1×10^?6 mol L^?1, and for determination 3‐aminofluorathnene in the concentration range of 2×10^?7–1×10^?5 mol L^?1, respectively. Limits of determination were 3×10^?8 mol L^?1 (3‐nitrofluoranthene) and 2×10^?7 mol L^?1 (3‐aminofluoranthene).     

Highly Thiocyanate‐Selective PVC Membrane Electrode Based on Lipophilic Ferrocene Derivative

A novel anion‐selective PVC membrane electrode based on bis‐[(3‐ferrocenyl)‐(2‐crotonic acid)] copper(II) complex [Cu(II)‐BFCA] as neutral carrier is described, which demonstrates excellent potentiometric response characteristics toward thiocyanate ion and anti‐Hofmeister selectivity sequence in following order: SCN^?>I^?>ClO >Sal^?>Br^?>NO >Cl^?≈NO >SO >SO . The electrode shows a near‐Nernstian response for thiocyanate ion in a wide range of 9.0×10^?7–1.0×10^?1 M with a detection limit 6.8×10^?7 M and a slope of ?59.1 mV/decade in pH 5.0 of phosphate buffer solution at 20 °C. The influences of lipophilic cationic and anionic additives on the response properties of the electrode were investigated. High sensitivity and wide linear dynamic range were observed for the electrode in the presence of hexadecyltrimethylammoniumborate (HTAB) as a lipophilic cationic additive. The electrode was successfully applied to the determination of thiocyanate ion in waste water and human saliva.     

Oxidation Behavior of Insecticide Azoxystrobin and its Voltammetric Determination Using Boron‐doped Diamond Electrode

Electrochemical oxidation of azoxystrobin, a systemic fungicide commonly used in agriculture to protect a wide variety of crops, was investigated using cyclic voltammetry with a boron‐doped diamond electrode (BDDE) in aqueous buffer solutions. Two pH independent irreversible anodic current peaks controlled mostly by diffusion were observed in wide pH range (2 to 12) at potentials +1600 mV and +2150 mV vs. saturated silver‐silver chloride electrode. Mechanism of the electrochemical oxidation was proposed and supported with high performance liquid chromatography/mass spectrometry analysis of azoxystrobin solutions electrolyzed on carbon fiber brush electrode. The main product of the first two‐electron oxidation step was identified as methyl 2‐(2‐{[6‐(2‐cyanophenoxy)pyrimidin‐4‐yl]oxy}phenyl)‐2‐hydroxy‐3‐oxopropanoate. An analytical method for the determination of azoxystrobin in water samples and pesticide preparation by differential pulse voltammetry with BDDE was developed. The method provides a wide linear dynamic range (3.0×10^?7 to 2.0×10^?4 mol L^?1) with limit of detection 8×10^?8 mol L^?1. Accuracy of the method was evaluated by the addition and recovery method with recoveries ranging from 96.0 to 105.8 %. Interference study proved sufficient selectivity of the developed voltammetric method for the azoxystrobin determination in presence of azole fungicides as well as pesticides used to prevent the same crops.     

Graphene‐Nafion Composite Film Modified Electrode for Voltammetric Sensor for Determination of Dihydromyricetin

A simple but highly snesitive electrochemical sensor for the determination of dihydromyricetin (DMY) based on graphene‐Nafion nanocomposite film modified Glassy carbon electrode (GCE) was reported. The characteristic of the sensor was examined by scanning electron microscopic (SEM) and electrochemical impedance spectroscopy (EIS). Compares with bare GCE, pre‐anodized glassy carbon electrode (GCE(ox)) and Nafion modified electrode, the sensor exhibited the more superior ability of detecting DMY, due to the synergetic graphene and Nafion. Other, the dependence of the current on pH, instrumental parameters, accumulation time and potential were investigated to optimize the experimental conditions in the determination of DMY. Under the selected conditions, the response peak currents were linear relationship with the DMY concentrations in the range of 8.0 × 10^?8 ～ 2.0 × 10^?5 mol L^?1 with a detection limit of 2.0 × 10^?8 mol L^?1. And, the method was also applied successfully to detect DMY in Ampelopsis grossedentata samples.