Application of a trazodone-selective electrode to pharmaceutical quality control and urine analyses

A trazodone-selective electrode for application in pharmaceutical quality control and urine analysis was developed. The electrode is based on incorporation of a trazodone-tetraphenylborate ion exchanger in a poly(vinyl chloride) membrane. The electrode showed a fast, stable and Nernstian response over a wide trazodone concentration range (5 × 10⁻⁵−1 × 10⁻² M) with a mean slope of 59.3 ± 0.9 mV/dec of concentration, a mean detection limit of 1.8 × 10⁻⁵± 2.2 × 10⁻⁶ M, a wide working pH range (5–7.5) and a fast response time (less than 20 s). The electrode also showed good accuracy, repeatability, reproducibility and selectivity with respect to some inorganic and organic compounds, including the main trazodone metabolite. The electrode provided good analytical results in the determination of trazodone in pharmaceuticals and spiked urine samples; no extraction steps were necessary. Dissolution testing of trazodone tablets, in different conditions of pH and particle size, based on a direct potentiometric determination with the new selective electrode is presented as well.     

Electrochemical oxidation of salicylic acid at well-aligned multiwalled carbon nanotube electrode and its detection

In this paper, an electrochemical sensor for sensitive and convenient determination of salicylic acid (SA) was constructed using well-aligned multiwalled carbon nanotubes as electrode material. Compared to the glassy carbon electrode, the electro-oxidation of SA significantly enhanced at the multiwalled carbon nanotube (MWCNT) electrode. The MWCNT electrode shows a sensitivity of 59.25 μA mM⁻¹, a low detection limit of 0.8 × 10⁻⁶ M and a good response linear range with SA concentration from 2.0 × 10⁻⁶ to 3.0 × 10⁻³ M. In addition, acetylsalicylic acid was determined indirectly after hydrolysis to SA and acetic acid, which simplified the detection process. The mechanism of electrochemical oxidation of SA at the MWCNT electrode is also discussed.     

Electrochemical methods for simultaneous determination of trace amounts of dopamine and uric acid using a carbon paste electrode incorporated with multi-wall carbon nanotubes and modified with α-cyclodextrine

In this work, we investigate the electrochemical activity of dopamine (DA) and uric acid (UA) using both a bare and a modified carbon paste electrode as the working electrode, with a platinum wire as the counter electrode and a silver/silver chloride (Ag/AgCl) as the reference electrode. The modified carbon paste electrode consists of multi-walled carbon nanotubes (>95%) treated with α-cyclodextrine, resulting in an electrode that exhibits a significant catalytic effect toward the electro-chemical oxidation of DA in a 0.2-M Britton–Robinson buffer solution (pH 5.0). The peak current increases linearly with the DA concentration within the molar concentration ranges of 2.0 × 10⁻⁶ to 5.0 × 10⁻⁵ M and 5.0 × 10⁻⁵ to 1.9 × 10⁻⁴ M. The detection limit (signal to noise >3) for DA was found to be 1.34 × 10⁻⁷ M, respectively. In this work, voltammetric methods such as cyclic voltammetry, chronoamperometry, chronocuolometry, differential pulse and square wave voltammetry, and linear sweep and hydrodynamic voltammetry were used. Cyclic voltammetry was used to investigate the redox properties of the modified electrode at various scan rates. The diffusion coefficient (D, cm² s⁻¹ = 3.05 × 10⁻⁵) and the kinetic parameters such as the electron transfer coefficient (α = 0.51) and the rate constant (k, cm³ mol⁻¹ s⁻¹ = 1.8 × 10³) for DA were determined using electrochemical approaches. By using differential pulse voltammetry for simultaneous measurements, we obtained two peaks for DA and UA in the same solution, with the peak separation approximately 136 mV. The average recovery was measured at 102.45% for DA injection.     

Determination of thiocyanate ions at nanolevel in real samples using coated graphite electrode based on synthesised macrocyclic Zn(II) complex

The electrode characteristics and selectivities of PVC-based thiocyanate selective polymeric membrane electrode (PME) incorporating the newly synthesized zinc complex of 6,7:14,15-Bzo₂-10,11-(4-methylbenzene)-[15]-6,8,12,14-tetraene-9,12-N₂-1,5-O₂ (I ₁ ) and zinc complex of 6,7:14,15-Bzo₂-10,11-(4-methylbenzene)-[15]-6,14-diene-9,12-dimethylacrylate-9,12-N₂-1,5-O₂ (I ₂ ) are reported here. The best response was observed with the membrane having a composition of I₂:PVC:o-NPOE:HTAB in the ratio of 6:33:59:2 (w/w; milligram). This electrode exhibited Nernstian slope for thiocyanate ions over working concentration range of 4.4 × 10⁻⁷ to 1.0 × 10⁻² mol L⁻¹ with detection limit of 2.2 × 10⁻⁷ mol L⁻¹. The performance of this electrode was compared with coated graphite electrode (CGE), which showed better response characteristics w.r.t Nernstian slope 59.0 ± 0.2 mV decade⁻¹ activity, wide concentration range of 8.9 × 10⁻⁸ to 1.0 × 10⁻² mol L⁻¹ and detection limit of 6.7 × 10⁻⁸ mol L⁻¹. The response time for CGE and PME was found to be 8 and 10 s, respectively. The proposed electrode (CGE) was successfully applied to direct determination of thiocyanate in biological and environmental samples and also as indicator electrode in potentiometric titration of SCN⁻ ion.     

Simultaneous and sensitive determination of procaine and its metabolite for pharmaceutical quality control and pharmacokinetic research by using a graphite paste electrode

A simple, rapid, sensitive, and accurate method for simultaneous electrochemical determination of procaine and its metabolite (p-aminobenzoic acid, PABA) for pharmaceutical quality control and pharmacokinetic research was developed using a graphite paste electrode. The differential pulse voltammetric results revealed that procaine and p-aminobenzoic acid, respectively, showed well-defined anodic oxidation peaks on a carbon paste electrode with a current peak separation of 155 mV at a scan rate of 100 mV s⁻¹. This well separation of the current peaks for these two compounds in voltammetry enables us to simultaneously determine them. Good linearity (r > 0.998) between oxidation peak current and concentration was obtained in the range of 5.0 × 10⁻⁷–5.0 × 10⁻⁵ M for procaine and 5.0 × 10⁻⁷–2.0 × 10⁻⁵ M for PABA in pH 4.50 acetate buffer solution. The detection limit for both analytes is 5 × 10⁻⁸ M (S/N = 3:1). The present voltammetric method has been successfully used to determine trace p-aminobenzoic acid in procaine hydrochloride injection and procaine in plasma with a linear relationship of current to its concentration ranging from 1.0 × 10⁻⁶ to 5.0 × 10⁻⁵ M (correlation coefficient of 0.9981) with a low detection limit of 5.0 × 10⁻⁷ M (S/N = 3:1). This validated method is promising to the study of pharmacokinetics in Sprague–Dawley rat and rabbit plasma after an intravenous administration of procaine hydrochloride injection.     

Subnanomolar determination of a beryllium ion by a novel Be(II) microsensor based on 4-nitrobenzo-9-crown-3-ether

In this work, for the first time, we introduce a highly selective and sensitive Be(II) microsensor. 4-nitrobenzo-9-crown-3-ether (NBCE) was used as a membrane-active component to prepare a Be(II)-selective polymeric membrane microelectrode. The electrode exhibits a Nernstian response toward Be(II) ions over a very wide concentration range (1.0 × 10⁻⁴–1.0 × 10⁻¹⁰ M), with a detection limit of 3.5 × 10⁻¹¹ M (∼350 pg/L). In fact, the electrode presents a fast response time in the whole concentration range (6 s). The proposed microelectrode can be used for at least six weeks without any considerable divergence in the potentials. The proposed membrane sensor revealed a selectivity toward Be(II) ions over a wide variety of other metal ions including common alkali, alkaline-earth, and rare-earth ions. It could be used in the pH range of 3.0–11.5. The microelectrode was successfully used as an indicator electrode for the titration of 20 mL of 1.0 × 10⁻⁶ M Be²⁺ solution with 1.0 × 10⁻⁴ M of EDTA. It was also applied to the direct determination of beryllium ions in beryl and binary mixtures. The text was submitted by the authors in English.     

Electrochemical detection of copper(II) at a gold electrode modified with a self-assembled monolayer of penicillamine

A penicillamine (PCA) self-assembled monolayer (SAM) was prepared on a gold electrode. It has been found that the modified electrode exhibited a selective response to copper ions. As demonstrated by cyclic voltammetric experiments, the SAM-based electrode showed an attractive ability to preconcentrate efficiently traces of copper(II) from solutions. Under optimum conditions, the anodic peak current was proportional to the concentration of Cu(II) in the range from 8.0 × 10⁻⁷ to 1.0 × 10⁻⁴ M with a detection limit of 4.0 × 10⁻⁷ M. Moreover, this modified gold electrode is also characterized by excellent repeatability, showing a relative standard deviation of 3.2% for nine successive measurements of 1.0 × 10⁻⁵ M Cu(II). The PCA/Au SAM gold electrode was used for the determination of Cu(II) in a tap water sample and the results showed a good agreement with the data obtained by atomic emission spectrometry. The text was submitted by the authors in English.     

Azide-selective sensor based on tripodal iron complex for direct azide determination in aqueous samples

A potentiometric azide-selective sensor based on the use of iron(III) hydrotris(3,5-dimethylpyrazolyl)borate acetylacetonate chloride [Tp^Me2Fe(acac)Cl] as a neutral carrier for an azide-selective electrode is reported. Effect of various plasticizers, viz. o-nitrophenyloctyl ether (o-NPOE), dioctylphthalate (DOP), dibutylphthalate (DBP), and benzylacetate (BA), and an anion excluder, hexadecyltrimethylammonium bromide (HTAB), with [Tp^Me2Fe(acac)Cl] complex in poly(vinyl chloride) (PVC) were studied. The best performance was obtained with a membrane composition of [Tp^Me2Fe(acac)Cl]/HTAB/DOP/PVC in a ratio of 5:2:190:100 (w/w). The sensor exhibits significantly enhanced selectivity toward azide ions over the concentration range 6.3 × 10⁻⁷ to 1.0 × 10⁻² M with a lower detection limit of 3.8 × 10^–7 M and a Nernstian slope of 59.4 ± 1.1 mV decade⁻¹. Influences of the membrane composition, pH and possible interfering anions were investigated on the response properties of the electrode. Fast and stable response, good reproducibility, long-term stability and applicability over a wide pH range (3.5–9.0) are demonstrated. The sensor has a response time of 14 s and can be used for at least 45 days without any considerable divergence in the potential response. The proposed electrode shows fairly good discrimination of azide from several inorganic and organic anions. It was successfully applied to the direct determination of azide in orange juice, tea extracts and human urine samples.     

Determination of copper(II) in wastewater by electroplating samples using a PVC-membrane copper(II)-selective electrode

A PVC membrane containing 4-amino-6-methyl-1,2,4-triazin-3,5-dithione (AMTD) as a suitable ionophore, exhibits a Nernstian response for Cu²⁺ ions over a wide concentration range up to 1 × 10⁻¹ and 1 × 10⁻⁶ M, with a detection limit of 7.5 × 10⁻⁷ M in the pH range 3.0–7.5. It has a fast response time (<15 s) and can be used for at least 12 weeks without any major deviation in the potential. The electrode revealed a very good selectivity with respect to all common alkali, alkaline-earth, transition, and heavy-metal ions. It was successfully applied to the recovery of copper ions from wastewater. The electrode was also used as an indicator electrode in the potentiometric titration of Cu(II) ions with EDTA. The text was submitted by the authors in English.     

Simultaneous determination of uric acid and ascorbic acid at the film of chitosan incorporating cetylpyridine bromide modified glassy carbon electrode

A glassy carbon electrode (GCE) modified with the film composed of chitosan incorporating cetylpyridine bromide is constructed and used to determine uric acid (UA) and ascorbic acid (AA) by differential pulse voltammetry (DPV). This modified electrode shows efficient electrocatalytic activity and fairly selective separation for oxidation of AA and UA in mixture solution. UA is catalyzed by this modified electrode in phosphate buffer solution (pH 4.0) with a decrease of 80 mV, while AA is catalyzed with a decrease of 200 mV in overpotential compared to GCE, and the peak separation of oxidation between AA and UA is 260 mV, which is large enough to allow the determination of one in presence of the other. Under the optimum conditions, the anodic peak currents (I _pa) of DPV are proportional to the concentration of UA in the range of 2.0 × 10⁻⁶ to 6.0 × 10⁻⁴ M, with the detection limit of 5.0 × 10⁻⁷ M at a signal-to-noise ratio of 3 (S/N = 3) and to that of AA in the range of 4.0 × 10⁻⁶ to 1.0 × 10⁻³ M, with the detection limit of 8.0 × 10⁻⁷ M (S/N = 3).     

Cetyldimethylethylammonium-Selective PVC Electrode Basedon its Ion-Associate with Phosphotungstic Acid

 A PVC membrane electrode selective for cetyldimethylethylammonium (CDEA) ion was prepared. The active element is a plasticized poly vinyl chloride membrane containing a dissolved ion associate complex of CDEA with phosphotungstic acid (PTA). The electrode showed a near-Nernstian response within the CDEA⁺ concentration range 2.34 × 10⁻⁶ to 1.96 × 10⁻⁴ M at 25 ± 1^{^}C, good selectivity, and is usable within the pH range 3.5–9.0. The isothermal temperature coefficient of the electrode amounted to −0.00012 V/°C. The electrode has been used for the direct determination of cetyldimethylethylammonium bromide either by the standard addition method or by potentiometric titration against PTA. Received January 1, 1998. Revision June 13, 2000.     

Adsorptive Voltammetric Studies on the Cerium(III)–Alizarin Complexon Complex at a Carbon Paste Electrode

A novel procedure was developed for the determination of trace cerium on the basis of anodic adsorption voltammetry of the Ce(III)–alizarin complexon (ALC) complex at a carbon paste electrode (CPE). The procedure is convenient to determine cerium individually in the presence of other rare earths because there is a 100 mV difference between the peak potentials of Ce(III)–ALC and other rare earth(III)–ALC complexes in a supporting electrolyte of 0.08 M HAc–NaAc and 0.012 M potassium biphthalate (pH 4.7) when performing linear-scanning from −0.2 to 0.8 V (vs. SCE) at 100 mV/s. The second-order derivative peak currents are directly proportional to the Ce(III) concentration over a range of 6.0 × 10⁻⁹–3.0 × 10⁻⁷ M. The detection limit is as low as 2.0 × 10⁻⁹ M (S/N = 3) for a 120 s preconcentration. An RSD of 3.5% was obtained for 15 determinations of Ce(III) at a concentration of 4.0 × 10⁻⁸ M on the same CPE surface. The method was applied successfully to the determination of cerium in samples of rare earth nodular graphite cast iron.     

Voltammetric detection of riboflavin based on ordered mesoporous carbon modified electrode

The potential application of ordered mesoporous carbon (OMC)-modified glassy carbon electrode (OMC/GCE) in electrochemistry as a novel electrode material was investigated. X-ray diffraction, transmission electron micrographs, and cyclic voltammetry were used to characterize the structure and electrochemical behaviors of this material. Compared to GC electrode, the peak currents of potassium ferricyanide (K₃[Fe(CN)₆]) increase and the peak potential separation (ΔE _p) decreases at the OMC/GC electrode. These phenomena suggest that OMC-modified GC electrode possesses larger electrode area and faster electron transfer rate, as compared with bare GC electrode. Furthermore, riboflavin was detected using OMC/GC electrode in aqueous solutions. The results showed that, under an optimum condition (pH 7.0), the OMC/GC electrode exhibited excellent response performance to riboflavin in the concentration range of 4.0 × 10⁻⁷ to 1.0 × 10⁻⁶ M with a high sensitivity of 769 μA mM⁻¹. The detection limit was down to around 2 × 10⁻⁸ M. With good stability and reproducibility, the present OMC/GC electrode was applied in the determination of vitamin B₂ content in vitamin tablets, and satisfactory results were obtained.     

Langmuir–Blodgett film of tetraoxocalix[2]arene[2]triazine modified electrode for voltammetric determination of copper ion

In the present work, a new voltammetric sensor, Langmuir–Blodgett (LB) film of tetraoxocalix[2]arene[2]triazine (TOCT) modified glassy carbon electrode (LB_TOCT-GCE), for trace analysis of copper ion in water samples, was prepared. The morphology of LB_TOCT-GCE was characterized by cyclic voltammetric method, electrochemical impedance spectroscopy, and atomic force microscope. The recognizing mechanism of LB_TOCT-GCE for copper ion in aqueous solution was discussed. Under the optimum experimental conditions, using square wave stripping voltammetry and accumulation time of 300 s, the peak currents were linear relationship with Cu²⁺ concentrations in the range of 2 × 10⁻⁹ to 1 × 10⁻⁶ mol L⁻¹, with detection limit of 1 × 10⁻¹⁰ mol L⁻¹. By this method, real samples (lake water, drinking water, and city wastewater) were analyzed with satisfactory results. In addition, the fabricated electrode exhibited a distinct advantage of simple preparation, non-toxicity, good reproducibility, and stability.     

Electrochemical behavior of uric acid at a penicillamine self-assembled gold electrode

The fabrication and electrochemical characteristics of a penicillamine (PCA) self-assembled monolayer modified gold electrode were investigated. The electrode can enhance the electrochemical response of uric acid (UA), and the electrochemical reaction of UA on the PCA electrode has been studied by cyclic voltammetry and differential pulse voltammetry. Some electrochemical parameters, such as diffusion coefficient, standard rate constant, electron transfer coefficient and proton transfer number have been determined for the electrochemical behavior on the PCA self-assembled monolayer electrode. The electrode reaction of UA is an irreversible process, which is controlled by the diffusion of UA with two electrons and two protons transfer at the PCA/Au electrode. In phosphate buffer (pH 5.0), the peak current is proportional to the concentration of UA in the range of 6.0 × 10⁻⁵–7.0 × 10⁻⁴ mol L⁻¹ and 2.0 × 10⁻⁵–7.0 × 10⁻⁴ mol L⁻¹ for the cyclic voltammetry and differential pulse voltammetry methods with the detection limits of 5.0 × 10⁻⁶ and 3.0 × 10⁻⁶ mol L⁻¹, respectively. The method can be applied to determine UA concentration in real samples.     

Fabrication of gold nanoparticles/polypyrrole composite-modified electrode for sensitive hydroxylamine sensor design

A highly sensitive hydroxylamine (HA) electrochemical sensor is developed based on electrodeposition of gold nanoparticles with diameter of 8 nm on the pre-synthesized polypyrrole matrix and formed gold nanoparticles/polypyrrole (GNPs/PPy) composite on glassy carbon electrode. The electrochemical behavior and electrocatalytic activity of the composite-modified electrode are investigated. The GNPs/PPy composite exhibits a distinctly higher electrocatalytic activity for the oxidation of HA than GNPs with twofold enhancement of peak current. The enhanced electrocatalytic activity is attributed to the synergic effect of the highly dispersed gold metal particles and PPy matrix. The overall numbers of electrons involved in HA oxidation, the electron transfer coefficient, catalytic rate constant, and diffusion coefficient are investigated by chronoamperometry. The sensor presents two wide linear ranges of 4.5 × 10⁻⁷–1.2 × 10⁻³ M and 1.2 × 10⁻³–19 × 10⁻³ M with the detection limit of 4.5 × 10⁻⁸ M (s/n = 3). In addition, the proposed electrode shows excellent sensitivity, selectivity, reproducibility, and stability properties.     

A novel lariat crown compound as ionophore for construction of a mercury(II)-selective electrode

Abstract  

The construction, performance, and application of a new PVC membrane electrode for determination of the mercury(II) ion, based on 8,17-bis(pyren-1-ylmethyl)-6,7,8,9,15,16,17,18-octahydrodibenzo[f,m][1,8,4,11]dithiadiazacyclotetradecine as an ionophore, is described. The effects of factors such as membrane composition, the nature and amount of the plasticizers and additives, and pH for the improved sensitivity of the electrode were studied. The electrode had a Nernstian response for mercury(II) ions over the concentration range 1.0 × 10⁻²–1.0 × 10⁻⁶ mol dm⁻³ with a slope of 27.6 ± 0.6 mV/pHg. The detection limit for mercury(II) was 7.9 × 10⁻⁷ mol dm⁻³. The response time of the electrode was between 5 and 15 s, depending on the concentration of mercury, and it can be used in a pH range 4.0–4.5 for approximately 4 months without any substantial divergence of the response characteristics. It showed higher selectivity for mercury(II) ions than for several common alkali, alkaline earth, and transition metal ions except silver(I). The proposed electrode was successfully applied to direct determination of mercury in a dental filling amalgam alloy as a real sample with a complex matrix and as an indicator electrode in complexation titrations.     

The complex (2,3;6,7;10,11;14,15-tetraphenyl-4,9,13,16-tetraoxo-1,5,8,12-tetraazacyclohexadecane) copper(II) as a carrier for a salicylate-sensitive poly(vinylchloride) membrane electrode

A new salicylate-selective electrode based on the complex (2,3;6,7;10,11;14,15-tetraphenyl-4,9,13,16-tetraoxo-1,5,8,12-tetraazacyclohexadecane) copper(II) [CuL] as the membrane carrier was developed. The electrode exhibits a good Nernstian slope of −60.9 ± 1.0 mV/decade and a linear range from 1.0 × 10⁻⁶ to 1.0 × 10⁻¹ M for salicylate. The detection limit is 5.0 × 10⁻⁷ M. The electrode has a fast response time (5–15 s) and can be used for more than three months. The selective coefficients were determined by the fixed interference method (FIM) and separate solution method (SSM). The salicylate-selective electrode could be used in the pH range 3.5–10.5. It was employed as an indicator electrode for direct determination of salicylate in pharmaceutical samples. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 9, pp. 1147–1154. The text was submitted by the authors in English.     

Construction and Evaluation of a Promazinium Cation-Selective Electrode

 The construction of a plasticised PVC matrix-type promazinium cation-selective membrane electrode and its use in the potentiometric determination of promazine hydrochloride in pharmaceutical preparations are described. It is based on the use of the ion-associate species, formed by promazinium cation and tetraphenylborate (TPB) counter ion. The basic electrode performance characteristics are evaluated according to IUPAC recommendations. It exhibited a linear response for 1 × 10⁻²−1 × 10⁻⁵ M of promazine hydrochloride solutions with a cationic Nernstian slope over the pH range 2–6. Common organic and inorganic cations showed negligible interference. Direct potentiometric determination of 1 × 10⁻²−1 × 10⁻⁵ M aqueous promazine hydrochloride using this membrane electrode system showed an average recovery of 99.5% with a mean standard deviation of 1.5%. This electrode was successfully used for monitoring the titration of promazine hydrochloride with sodium tetraphenyl borate and for determining promazine hydrochloride in ampoules. Received June 15, 2001 Revision November 6, 2001     

Electrochemical behavior and determination of epinephrine at a mercaptoacetic acid self-assembled gold electrode

The electrochemical behavior of epinephrine (EP) at a mercaptoacetic acid (MAA) self-assembled monolayer modified gold electrode was studied. The MAA/Au electrode is demonstrated to promote the electrochemical response of epinephrine by cyclic voltammetry. The possible reaction mechanism is also discussed. The diffusion coefficient D of EP is 6.85 × 10⁻⁶ cm² s⁻¹. In 0.1 mol L⁻¹ phosphate buffer (pH 7.20), a sensitive oxidation peak was observed at 0.177 V, and the peak current is proportional to the concentration of EP in the range of 1.0 × 10⁻⁵–2.0 × 10⁻⁴ mol L⁻¹ and 1.0 × 10⁻⁷–1.0 × 10⁻⁶ mol L⁻¹. The detection limit is 5 × 10⁻⁸ mol L⁻¹. The modified electrode is highly stable and can be applied to the determination of EP in practical injection samples. The method is simple, quick, sensitive and accurate.