Voltammetric sensor based on carbon paste electrode modified with molecular imprinted polymer for determination of sulfadiazine in milk and human serum

A new sensitive voltammetric sensor for determination of sulfadiazine is described. The developed sensor is based on carbon paste electrode modified with sulfadiazine imprinted polymer (MIP) as a recognition element. For comparison, a non-imprinted polymer (NIP) modified carbon paste electrode was prepared. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods were performed to study the binding event and electrochemical behavior of sulfadiazine at the modified carbon paste electrodes. The determination of sulfadiazine after its extraction onto the electrode surface was carried out by DPV at 0.92 V vs. Ag/AgCl owing to oxidation of sulfadiazine. Under the optimized operational conditions, the peak current obtained at the MIP modified carbon paste electrode was proportional to the sulfadiazine concentration within the range of 2.0 × 10^? 7–1.0 × 10^? 4 mol L^? 1 with a detection limit and sensitivity of 1.4 × 10^? 7 mol L^? 1 and 4.2 × 10⁵ μA L mol^? 1, respectively. The reproducibility of the developed sensor in terms of relative standard deviation was 2.6%. The sensor was successfully applied for determination of sulfadiazine in spiked cow milk and human serum samples with recovery values in the range of 96.7–100.9%.     

Electrochemical sensor for ranitidine determination based on carbon paste electrode modified with oxovanadium (IV) salen complex

The preparation and electrochemical characterization of a carbon paste electrode modified with the N,N-ethylene-bis(salicyllideneiminato)oxovanadium (IV) complex ([VO(salen)]) as well as its application for ranitidine determination are described. The electrochemical behavior of the modified electrode for the electroreduction of ranitidine was investigated using cyclic voltammetry, and analytical curves were obtained for ranitidine using linear sweep voltammetry (LSV) under optimized conditions. The best voltammetric response was obtained for an electrode composition of 20% (m/m) [VO(salen)] in the paste, 0.10 mol L^? 1 of KCl solution (pH 5.5 adjusted with HCl) as supporting electrolyte and scan rate of 25 mV s^? 1. A sensitive linear voltammetric response for ranitidine was obtained in the concentration range from 9.9 × 10^? 5 to 1.0 × 10^? 3 mol L^? 1, with a detection limit of 6.6 × 10^? 5 mol L^? 1 using linear sweep voltammetry. These results demonstrated the viability of this modified electrode as a sensor for determination, quality control and routine analysis of ranitidine in pharmaceutical formulations.     

Designing and synthesis of bis(2,4-dihydroxybenzylidene)-1,6-diaminohexane and its efficient application as neutral carrier for preparation of new copper selective electrode

A new copper carbon paste electrode (CPE) based on incorporation bis(2, 4-dihydroxybenzyliden)-1,6-diaminohexane (DHBDAH) in graphite powder matrix has been described. The influence of variables including an amount of graphite, sodium tetraphenylborate (NaTPB), DHBDAH and nujol on the Cu²⁺ carbon paste electrode response was studied and optimized. The optimum carbon paste composition was set as follows, graphite powder: NaTPB: Nujol: DHBDAH with amount of 150:2.3:30:4 mg, respectively. At the optimum conditions, the potential response is linear over the concentration range of 5.0 × 10^? 8 to 1.0 × 10^? 1 mol L^? 1 with a Nernstian slope of 29.5 ± 1.1 mV per decade of Cu²⁺ ion concentration. The good performance of electrode such as low detection limit of (LOD) (4 × 10^? 8 mol L^? 1), wide applicable pH range (2.5–5.5), fast response time (?10 s) and adequate shelf life (69 days) indicate the utility of the proposed electrode for evaluation of Cu²⁺ ion content in various analysis. Due to moderate potentiometric selectivity coefficients of proposed electrode obtained by fixed interference method (FIM) and separate solution method (SSM), the proposed electrode successfully can be applied for the determination of Cu²⁺ ions content in some real samples.     

A simple and efficient electrochemical sensor for folic acid determination in human blood plasma based on gold nanoparticles–modified carbon paste electrode

Folic acid (FA) is a water soluble vitamin that exists in many natural species. The lack of FA causes some deficiencies in human body, so finding a simple and sensitive method for determining the FA is important. A new chemically modified electrode was fabricated for determination of FA in human blood plasma using gold nanoparticles (AuNPs) and carbon paste electrode (CPE). Gold nanoparticles–modified carbon paste electrode (AuNPs/CPE) was characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The experimental parameters such as pH, scan rate (ν) and amount of modifier were studied by cyclic voltammetry and the optimized values were chosen. The electrochemical parameters such as diffusion coefficient of FA (D_FA), electrode surface area (A) and electron transfer coefficient (α) were calculated. Square wave voltammetry as an accurate technique was used for quantitative calculations. A good linear relation was observed between anodic peak current (i_pa) and FA concentration (C_FA) in the range of 6 × 10^? 8 to 8 × 10^? 5 mol L^? 1, and the detection limit (LOD) achieved 2.7 × 10^? 8 mol L^? 1, that is comparable with recently studies. This paper demonstrated a novel, simple, selective and rapid sensor for determining the FA in the biological samples.     

Determination of Pb2+ ions by a modified carbon paste electrode based on multi-walled carbon nanotubes (MWCNTs) and nanosilica

A novel carbon paste ion selective electrode for determination of trace amount of lead was prepared. Multi-walled carbon nanotubes (MWCNTs) and nanosilica were used for improvement of a lead carbon paste sensor response. MWCNTs have a good conductivity which helps the transduction of the signal in carbon paste electrode. The electrode composition of 20 wt% paraffin oil, 57% graphite powder, 15% ionophore (thiram), 5% MWCNTs, and 3% nanosilica showed the stable potential response to Pb²⁺ ions with the Nernstian slope of 29.8 (±0.2) mV decade^?1 over a wide linear concentration range of 10^?7–10^?2 mol L^?1. The electrode has fast response time, and long term stability (more than 2 months). The proposed electrode was used to determine the concentration of lead ions in waste water and black tea samples.     

Direct electrodeposition of gold nanotube arrays of rough and porous wall by cyclic voltammetry and its applications of simultaneous determination of ascorbic acid and uric acid

Gold nanotube arrays of rough and porous wall has been synthesized by direct electrodeposition with cyclic voltammetry utilizing anodic aluminum oxide template (AAO) and polycarbonate membrane (PC) during short time (only 3 min and 2 min, respectively). The mechanism of the direct electrodeposition of gold nanotube arrays by cyclic voltammetry (CV) has been discussed. The morphological characterizations of the gold nanotube arrays have been investigated by scanning electron microscopy (SEM). A simultaneous determination of ascorbic acid (AA) and uric acid (UA) by differential pulse voltammetry (DPV) was constructed by attaching gold nanotube arrays (using AAO) onto the surface of a glassy carbon electrode (GCE). The electrochemical behavior of AA and UA at this modified electrode has been studied by CV and differential pulse voltammetry (DPV). The sensor offers an excellent response for AA and UA and the linear response range for AA and UA were 1.02 × 10^? 7–5.23 × 10^? 4 mol L^? 1 and 1.43 × 10^? 7–4.64 × 10^? 4 mol L^? 1, the detection limits were 1.12 × 10^? 8 mol L^? 1 and 2.24 × 10^? 8 mol L^? 1, respectively. This sensor shows good regeneration, stability and selectivity and has been used for the determination of AA and UA in real human urine and serum samples with satisfied results.     

Application of ionic liquid–TiO2 nanoparticle modified carbon paste electrode for the voltammetric determination of benserazide in biological samples

An ionic liquid–TiO₂ nanoparticle modified carbon paste electrode (IL–TiO₂/CPE) was used as a fast and sensitive tool for the investigation of the electrochemical oxidation of benserazide using voltammetry. This modified electrode has been fabricated using hydrophilic ionic liquid (n-hexyl-3-methylimidazolium hexafluoro phosphate) as a binder. The modified electrode offers a considerable improvement in voltammetric sensitivity toward benserazide, compared to the bare electrode. Using differential pulse voltammetry (DPV), the electrocatalytic oxidation peak current of benserazide shows a linear calibration curve in the range of 1.0–600 μmol L^? 1 benserazide. The limit of detection was equal to 0.4 μmol L^? 1. The relative standard deviation (RSD%) for eight successive assays of 10 μmol L^? 1 benserazide was 1.1%. Finally, the proposed method was successfully applied to the determination of benserazide in real samples such as blood serum and urine.     

Determination of ultratrace levels of lead (II) in water samples using a modified carbon paste electrode based on a new podand

A new podand of 1,1′-thiobis(naphthalene-2,1-diyl)bis(2-aminobenzoate) (TNBA) was synthesized and used as a suitable carrier for construction of Pb²⁺ modified carbon paste electrode (CPE). The effects of various plasticizers; 2-nitrophenyloctylether (o-NPOE), dioctyl pththalate (DOP), dibutyl phthalate (DBP) and paraffin oil were studied. The best performance was obtained with a matrix composition of CPE with a DOP/graphite powder/TNBA weight percent ratio of 35/60.5/4.5. The sensor exhibits significantly enhanced selectivity toward Pb²⁺ ion over the concentration range 8.0 × 10^? 8 to 1.0 × 10^? 2 mol L^? 1 with a lower detection limit of 5.0 × 10^? 8 mol L^? 1 and a Nernstian slope of 29.0 ± 0.2 mV decade^? 1 of lead activity. It has a fast response time of 8 s with a working pH range from 3.5 to 7. The interaction between TNBA and Pb²⁺ was studied spectrophotometrically and it exhibits that the stoichiometry of the complex is 1:1 in acetonitrile solution. Finally, the electrode was satisfactorily used as an indicator electrode in complexometric titration of Pb²⁺ with EDTA and in direct determination of lead in various water samples.     

Modified carbon paste electrodes for Cu(II) determination

A new Cu²⁺ carbon paste electrode (CPE) using 2,2′-(1E,1′E)-1,1′-(2,2′-azanediylbis (ethane-2,1-diyl)bis(azan-1-yl-1-ylidene))bis(ethan-1-yl-1-ylidene)diphenol (ADEZEDP) has been prepared. The influence of variables including sodium tetraphenylborate (NaTPB), ionophore, and amount of multiwalled carbon nanotubes (MWCNT), CdO nanowires, CdS nanoparticles and palladium nanoparticles loaded on ADEZEDP and Nujol on the electrodes response were studied and optimized. At optimum values of all variables, for each nanomaterial the electrode response was linear in concentration range of 1.0 × 10^? 8 to 1.0 × 10^? 1 mol L^? 1 for ADEZEDP with Nernstian slope. The good performance of electrode viz. Wide applicable pH range (2.0–5.0), fast response time (≈ 6 s), and adequate life time (3 months) indicate the utility of the proposed electrodes for evaluation of Cu²⁺ ion content in various situations. Finally, these electrodes have been successfully applied for the determination of Cu²⁺ ions content in various real samples. The selectivity of proposed electrode was evaluated by separation solution method and fixed interference method.     

Hexadecylpyridinium surfactant modified zeolite A as an active component of a polymeric membrane sulfite selective electrode

Zeolite A was synthesized from waste porcelain and modified by hexadecylpyridinium surfactant to change the cation exchanger property of the raw zeolite to anion exchanger property in the obtained surfactant modified zeolite (SMZ). The SMZ was used as an active ingredient component of a membrane selective sulfite electrode. The electrode was fully characterized in terms of composition, response time, thermal stability and usable pH range. The sensor showed suitable response to sulfite in the concentration range of 8.0 × 10^? 7 to 1.0 × 10^? 1 mol L^? 1, with a detection limit of 5.0 × 10^? 7 mol L^? 1 and a slope of ? 29.5 ± 0.8 mV per decade of sulfite concentration.     

Nickel analysis in real samples by Ni2 + selective PVC membrane electrode based on a new Schiff base

A newly synthesized Schiff base 3-aminoacetophenonesemicarbazone (AAS) has been used for the preparation of Ni^2 + selective PVC membrane electrode. The proposed electrode exhibits a Nernstian response over the nickel concentration range of 1.0 × 10^? 7 to 1.0 × 10^? 2 mol L^? 1 with a slope of 30.0 ± 0.3 mV/decade of concentration. The limit of detection as determined from the intersection linear segment of the calibration plot is 5.1 × 10^? 8 mol L^? 1. The electrode shows good selectivity towards nickel with respect to several alkali, alkaline earth, transition and heavy metal ions. The response time of the electrode is very fast (≥ 10 s) and can be used for 17 weeks in the pH range of 2.0–9.8. The electrode can also be used in partially non-aqueous media having up to 20% (v/v) methanol, ethanol or acetone content with no significant change in the value of slope or working concentration range. To investigate the analytical applicability of the electrode, it was successfully applied as an indicator electrode in Ni^2 + ion potentiometric titration with EDTA, and in direct determination of nickel(II) in real samples.     

Quantitative monitoring of terbium ion by a Tb3+ selective electrode based on a new Schiff's base

Solution study showed N,N′-bis(5-nitrosalicylidene)-2-aminobenzylamin (L) trends toward Tb³⁺ ion. Then, it was used as a suitable ionophore in construction of terbium ion selective electrode. The electrode with composition of 30% PVC, 65% solvent mediator (NB), 3% ionophore (L) and 2% anionic additive (NaTPB) shows the best potentiometric response characteristics. It displays a Nernstian behavior (20.1 mV decade^?1) over the concentration range 1.0 × 10^? 6 to 1.0 × 10^? 2 mol L^?1. The detection limit of the electrode is 6.3 × 10^? 7 mol L^?1. It has a very short response time (~ 10 s) and a useful working pH range of 2.6–9.4 for at least 2 months. The proposed membrane sensor shows excellent discriminating ability towards Tb³⁺ ions with regard to several alkali, alkaline earth, transition and heavy metal ions. To investigate the analytical applicability of the sensor, it was successfully applied to the determination of terbium in certified reference material.     

Electrochemical sensor for selective determination of N-acetylcysteine in the presence of folic acid using a modified carbon nanotube paste electrode

In the present paper, a novel benzoylferrocene (BF) modified carbon nanotube paste electrode (BFCNPE) was prepared. The modified electrode was further used for the successful determination of N-acetylcysteine (NAC), and it showed an excellent electrocatalytic oxidation activity toward NAC with a lower overvoltage, pronounced current response, and good sensitivity. Under the optimized experimental conditions, the proposed electrochemical NAC sensor exhibited a linear calibration plot that ranged from 3.0 × 10^? 7 to 7.0 × 10^? 4 M with a detection limit of 9.0 × 10^? 8 M. Also, Square wave voltammetry (SWV) was used for simultaneous determination of NAC and folic acid (FA) at the modified electrode. Finally, the proposed method was applied to the determination of NAC in NAC tablets.     

Application of functionalized ZnS nanoparticles to determinate uracil and thymine as a fluorescence probe

ZnS nanoparticles were prepared by hydrothermal method and modified with mercaptoacetic acid in this paper. The functionalized nanoparticles were characterized using transmission electron microscopy (TEM), X-ray diffractometer (XRD) and photoluminescence spectroscopy. They were used as fluorescence probes in the determination of uracil and thymine. Under the optimum conditions, the fluorescence of functionalized ZnS nanoparticles was quenched by uracil and thymine, respectively. The responses are linearly proportional to the concentrations of uracil and thymine both between 0.8 × 10^?5 and 9.6 × 10^?5 mol L^?1and the limits of detection are 0.9 × 10^?6 and 0.4 × 10^?5 mol L^?1 for uracil and thymine, respectively.     

Gadolinium(III) ion selective sensor using a new synthesized Schiff's base as a sensing material

According to a solution study which showed a selective complexation between N,N′-bis(methylsalicylidene)-2-aminobenzylamine (MSAB) and gadolinium ions, MSAB was used as a sensing element in construction of a gadolinium(III) ion selective electrode. Acetophenon (AP) was used as solvent mediator and sodium tetraphenyl borate (NaTPB) as an anion excluder. The electrode showed a good selectivity towards Gd(III) ions over a wide variety of cations tested. The constructed sensor displayed a Nernstian behavior (19.7 ± 0.3 mV/decade) in the concentration range of 1.0 × 10^? 6 to 1.0 × 10^? 2 mol L^? 1 with detection limit of 5.0 × 10^? 7 mol L^? 1 and a short response time (< 10 s). The working pH range of the electrode was 3.5–10.1 and lifetime of the sensor was at least 10 weeks. Analysis of certified reference materials confirmed the accuracy of the proposed sensor. The electrode was successfully applied as an indicator electrode in gadolinium titration with EDTA.     

An optical chemical sensor for thorium (IV) determination based on thorin

A selective method for the determination of thorium (IV) using an optical sensor is described. The sensing membrane is prepared by immobilization of thorin–methyltrioctylammonium ion pair on triacetylcellulose polymer. The sensor produced a linear response for thorium (IV) concentration in the range of 6.46 × 10^?6 to 9.91 × 10^?5 mol L^?1 with detection limit of 1.85 × 10^?6 mol L^?1. The regeneration of optode was accomplished completely at a short time (less than 20 s) with 0.1 mol L^?1 of oxalate ion solution. The relative standard deviation for ten replicate measurements of 2.15 × 10^?5 and 8.62 × 10^?5 mol L^?1 of thorium was 2.71 and 1.65%, respectively. The optode membrane exhibits good selectivity for thorium (IV) over several other ionic species and are comparable to those obtained in case of spectrophotometric determination of thorium using thorin in solution. A good agreement with the ICP-MS and spiked method was achieved when the proposed optode was applied to the determination of thorium (IV) in dust and water samples.     

Simultaneous determination of phenylhydrazine and hydrazine by a nanostructured electrochemical sensor

In the present paper, the use of a nanostructured electrochemical sensor was described for simultaneous determination of phenylhydrazine (PhH) and hydrazine (HZ). This electrochemical sensor was prepared by a simple and rapid method by modification of carbon paste electrode with a derivative of hydroquinone and TiO₂ nanoparticles. The modified electrode showed an excellent character for electrocatalytic oxidation of PhH. Using differential pulse voltammetry, a highly selective and simultaneous determination of PhH and HZ has been explored at the modified electrode. Differential pulse voltammetry peak currents of PhH and HZ increased linearly with their concentration at the ranges of 2.0 × 10^? 6 to 1.0 × 10^? 3 M and 7.5 × 10^? 5–1.0 × 10^? 3 M, respectively and the detection limits for PhH and HZ were 7.5 × 10^? 7 M and 9.0 × 10^? 6 M, respectively.     

A comparative study on fabrication of Mn2 + selective polymeric membrane electrode and coated graphite electrode

Poly(vinyl chloride)-based membranes of two ligands 2,4-bis(2-acetoxybenzylamino)-6-phenyl-1,3,5-triazine (L₁) and N2,N4-di(cyanoethyl)-2,4-bis(2-acetoxybenzylamino)-6-phenyl-1,3,5-triazine (L₂) were fabricated and explored as Mn^2 + ion selective electrodes. The performance of the polymeric membranes electrodes of ionophores with different plasticizers (dibutylphthalate, benzoic acid, o-nitrophenyloctyl ether, 1-chloronapthalene and tri-n-butylphosphate) and anion excluders (sodium tetraphenylborate and potassium tetrakis p-(chloro phenyl)borate) was looked in to and the better results were obtained with the membrane having composition L₂: NaTPB: DBP: PVC as 6: 3: 56: 35 (w/w; mg). The coated graphite electrode (CGE) with same composition was also fabricated and investigated as Mn^2 + selective electrode. It was found that CGE showed better response characteristics than PME. The potentiometric response of CGE was independent of pH in the range 3.0–9.0 exhibiting the Nernstian slope 29.5 ± 0.3 mV decade^? 1 of activity and working concentration range 4.1 × 10^? 7–1.0 × 10^? 1 mol L^? 1 with a limit of detection 6.7 × 10^? 8 mol L^? 1. The electrode showed a fast response time of 12 s with a shelf life of 105 days. The proposed CGE could be successfully used for the determination of Mn^2 + ions in different water, soil, vegetables and medicinal plants also used as an indicator electrode in potentiometric titration with EDTA.     

Potentiometric detection of silver (I) ion based on carbon paste electrode modified with diazo-thiophenol-functionalized nanoporous silica gel

For the first time, triazene compound functionalized silica gel was incorporated into carbon paste electrode for the potentiometric detection of silver (I) ion. A novel diazo-thiophenol-functionalized silica gel (DTPSG) was synthesized, and the presence of DTPSG acted as not only a paste binder, but also a reactive material. The electrode with optimum composition, exhibited an excellent Nernstian response to Ag⁺ ion ranging from 1.0 × 10^? 6 to 1.0 × 10^? 1 M with a detection limit of 9.5 × 10^? 7 M and a slope of 60.4 ± 0.2 mV dec^? 1 over a wide pH range (4.0–9.0) with a fast response time (50 s) at 25 °C. The electrode also showed a long-time stability, high selectivity and reproducibility. The response mechanism of the proposed electrode was investigated by using AC impedance. Moreover, the electrode was successfully applied for the determination of silver ions in radiology films, and for potentiometric titration of the mixture solution of Cl^? and Br^? ions.     

Dysprosium selective potentiometric membrane sensor

A novel Dy(III) ion-selective PVC membrane sensor was made using a new synthesized organic compound, 3,4-diamino-N′-((pyridin-2-yl)methylene)benzohydrazide (L) as an excellent sensing element. The electrode showed a Nernstian slope of 19.8 ± 0.6 mV per decade in a wide concentration range of 1.0 × 10^? 6–1.0 × 10^? 2 mol L^? 1, a detection limit of 5.5 × 10^? 7 mol L^? 1, a short conditioning time, a fast response time (< 10 s), and high selectivity towards Dy(III) ion in contrast to other cations. The proposed sensor was successfully used as an indicator electrode in the potentiometric titration of Dy(III) ions with EDTA. The membrane sensor was also applied to the F^– ion indirect determination of some mouth washing solutions and to the Dy^3 + determination in binary mixtures.