Dehydrogenation of 1,2,3,4-tetrahydroquinoline and its related compounds: comparison of Pd/C-ethylene system and activated carbon-O2 system

Dehydrogenation of substituted 1,2,3,4-tetrahydroquinoline, 1,2,3,4-tetrahydroisoquinoline, and 1,2,3,4-tetrahydrocarbazole proceeded using Pd/C-ethylene system (method A) or activated carbon-O₂ system (method B) to give the corresponding heteroaromatic compounds.     

Ion-Selective Electrode for the Determination of Furaltadone

ABSTRACT

A Furaltadone (FD) ion-selective PVC membrane electrode based on the ion-pair complex of FD with sodium tetraphenylborate was prepared with dioctyl phthalate as a plasticiser. The electrode exhibits a linear response with an approximate Nernstian slope (50 mV decade^?1 at 20 ⁰C) with the concentration range 2.18 x 10^?5–2.18 x 10^?4 FD. The effects of ionic strength and pH of the test solution on the electrode performance were studied. The electrode exhibited very good selectivity for FD with respect to a large number of inorganic and organic cations of biological importance. The standard addition method and potentiometric titration were used to determine the FD in pure solution and in pharmaceutical preparations with satisfactory results.     

Die massenspektrometrische Retro-Diels-Alder-Reaktion: 1,2,3,4-Tetrahydrocarbazol. 30. Mitteilung über massenspektrometrische Untersuchungen

The mass spectral retro Diels-Alder-reaction: 1,2,3,4-tetrahydrocarbazole 1,2,3,4-Tetrahydrocarbazole undergoes a retro Diels-Alder-reaction under electron impact. C(2) and C(3) are eliminated as ethylene. This is shown by measuring the deuterated derivatives 1a , 1b and 1c . Furthermore the oxo-1,2,3,4-tetrahydrocarbazole derivatives 3 and 4 are investigated in respect to the mass spectral retro Diels-Alder reaction too.     

Highly Selective Potassium Ion Responsive Liquid-Membrane Electrode

Abstract

The performance of a new liquid-membrane electrode using valinomycin as membrane component is described with respect to selectivity, working range, speed of response and accuracy. The electrode makes possible the measurement of potassium ion activities in the range of 10^?1 M to at least 10^?6 M in unbuffered systems with a selectivity of potassium over sodium ions of more than 4,000. The electrode was used for the direct titration of potassium ions.     

Disopyramide-Selective Membrane Electrode∗

Abstract

A liquid membrane electrode based on disopyramide - dipicrylamine ion - pair complex, dissolved in nitrobenzene as solvent was proposed for the determination of disopyramide - an antiarrhythmic drug. The linear response covers the range from 10^?2 - 5 × 10^?6 M disopyramide solution, with a slope of 51.0 mV/decade (pH range 3.0 to 7.0). The detection limit is 4.7 × 10^?8 M. The electrode shows a good stability, reproducibility and fast response. The selectivity of the electrode is good. The strong interfering ion is thiamine (Vitamin B₁). These characteristics of the electrode made it to be used for the determination of disopyramide through direct and indirect potentiometric methods. Through indirect potentiometric method, disopyramide - as active substance can be determined with an average recovery of 99.98% and a relative standard deviation of 0.24%, and also this method can be used for its determination in pharmaceutical formulations such as capsules and ampoules with a relative standard deviation less than 1%. The electrode can be used at the dissolution tests of disopyramide capsules. The physical processes are numerically simulated by typical equations. The apparent first - order rate constants for disintegration and dissolution processes were calculated.

     

An Ion-Selective Electrode for Dibasic Phosphate Ion

Abstract

A phosphate-selective electrode is developed based on a silver coordination reaction. The electrode responds linearly toward HPO₄ ⁼ in the concentration range of 10^?4 to 10^?1 M (slope = 27 mV/dec.). The electrode also shows good selectivity over sulfate, nitrate, perchlorate and acetate.     

Zeolite-Modified Sol-Gel Electrode as an Electrochemical Sensor for Potentiometric Determination of Cesium Ions in Water Samples

Abstract

In this research, new electrodes were prepared by incorporating zeolite KY into sol-gel matrix. Calibration plot with Nernstian slope (58.6 ± 0.5 mV/decade) for cesium ion was observed over a linear range of about four decades of concentration (1.0 × 10^?5 to 1.0 × 10^?1 M, at 25°C). The sol-gel electrode shows detection limit of 7.3 × 10^?6 M. The influences of membrane composition, the pH of the test solution, and the interfering ions on the electrode performance were investigated. The effect of temperature on the electrode response showed that the temperature higher than 60°C deteriorates the electrode performance. The proposed electrode has high mechanical and thermal stability with a low isothermal temperature coefficient, and it is 0.00018 V/°C. It has a short response time (10 s) and can be used for more than 6 months without any considerable divergence in the potentials. The selectivity coefficients for Cs⁺ ion with respect to alkali, alkaline earth, ammonium, and some heavy-metal ions were investigated. The results of application show that the electrode can be used successfully in determination of Cs⁺ ions in various water samples.     

Voltammetric Determination of Uric Acid with a Glassy Carbon Electrode Coated by Paste of Multiwalled Carbon Nanotubes and Ionic Liquid

The voltammetric behavior of uric acid (UA) has been studied at a multiwalled carbon nanotube‐ionic liquid (i.e., 1‐butyl‐3‐methylimidazolium hexafluorophosphate, BMIMPF₆) paste coated glassy carbon electrode (MWNTs‐BMIMPF₆/GC). It is found that UA can effectively accumulate at this electrode and cause a sensitive anodic peak at about 0.49 V (vs. SCE) in pH 4.0 phosphate buffer solutions. Experimental parameters influencing the response of the electrode, such as solution pH and accumulation time, are optimized for uric acid determination. Under the optimum conditions, the anodic peak current is linear to UA concentration in the range of 1.0×10^?8 M to 1.0×10^?6 M and 2.0×10^?6 M to 2.0×10^?5 M. The detection limit is 5.0×10^?9 M for 180 s accumulation on open circuit. The electrode can be regenerated by successively cycling in a blank solution for about 3 min and exhibits good reproducibility. A 1.0×10^?6 M UA solution is measured for eight times using the same electrode regenerated after every determination, and the relative standard deviation (RSD) of the peak current is 3.2%. As for different electrodes fabricated by the same way the RSD (i.e., the electrode to electrode deviation) is 4.2%(n=9). This method has been applied to the determination of UA in human urine samples, and the recoveries are 99%–100.6%. In addition, comparison is made between MWNTs‐BMIMPF₆/GC and MWNTs/GC. Results show that the MWNTs‐BMIMPF₆/GC exhibits higher sensitivity, selectivity and ratio of peak current to background current.     

A Heterogeneous Precipitate Based Mn(Ii) Coated Wire Ion-Selective Electrode

Abstract

A new heterogeneous Mn(II) ion selective coated wire electrode (CWISE) based on tetrapyridine Mn(II) thiocynanate as electroactive material has been described. the working pH range of the electrode is 2.3 to 8.8. the electrode shows a linear response in the concentration range 1.0×10^?1M to 1.0×10^?6M. the response time of the electrode is 35 sec. the selectivity coefficient for different cations determined by mixed solution method are:

Fe²⁺(0.05), Cd²⁺(0.05), Ni²⁺(0.01), Co²⁺(0.5), Pb²⁺(0.5), Hg²⁺(0.05), Sn²⁺(0), Zn²⁺(0)

The electrode can be used for the electrometeric determination of Mn(II) ion.     

Poly(Vinyl Chloride) Containing Dibenzo-18-crown-6 as an Ion-Selective Membrane for Hyamine 1622

Abstract

A poly(vinyl chloride) membrane ion-selective electrode for the Hyamine 1622 cation is proposed. The active substance of the electrode was the neutral carrier dibenzo-18-crown-6 and di-iso-octylphthalate was used as plasticizer. The electrode had a Nernstian behaviour between 6.0 × 10^?6 and 1.6 × 10^?3 mol/dm³, a pH working range of 2 – 12 and high selectivity towards inorganic cations. Among the organic cations tested, only those having surfactant properties did interface. The electrode was suitable for determining the critical micelle concentration and as end-point detector in the potentiometric titration of the cationic surfactants.     

Imprinted Polymer – Modified Hanging Mercury Drop Electrode for Differential Pulse Adsorptive Stripping Voltammetric Analysis of a Diquat Herbicide

An imprinted polymer modified hanging mercury drop electrode (HMDE) in Model 303A system in conjunction with a PAR Model 264A Polarographic Analyzer/Stripping Voltammeter has been used for the selective analysis of a diquat herbicide viz., 5,6‐dihydropyrazino[1,2,3,4‐[lmn]‐1,10‐phenanthrolinium dichlorides in differential pulse cathodic stripping voltammetry mode. Complex aqueous samples (drinking water and agricultural soil suspension), spiked with a diquat herbicide, were directly analyzed by the adsorptive accumulation of the analyte over the working electrode (accumulation potential ?0.8 V (vs. Ag/AgCl), accumulation time 120 s, pH 7.0, supporting electrolyte 0.1 M KCl, scan rate 10 mV s^?1, pulse amplitude 25 mV). The limit of detection for diquat herbicide was found to be 0.34 nmol L^?1 (0.1 ppb, RSD 2%, S/N=2).     

Original Potentiometric Ytterbium(III) PVC-Membrane Sensor Based on N1,N2-Bis-[1-(2-hydroxy-1,2-diphenyl)ethylidene]ethanedihydrazide

Abstract

In this work, we describe the construction, performance, and applications of an original ytterbium(III) sensor based on N¹,N²-bis-[1-(2-hydroxy-1,2-diphenyl)ethylidene]ethanedihydrazide (BHDEH), which acts as a suitable carrier. Because it has a low detection limit of 4.2 × 10^?7 M, the sensor response for the Yb(III) ion is Nernstian over a wide concentration range: four decades of concentration (1.0 × 10^?6 to 1.0 × 10^?2 M). The response time of the electrode is less than 10 s, it can be used in the pH range of 3.2–8.3, and its duration is at least 2 months without any considerable potential divergence. The sensor revealed very good selectivity for Yb(III) in the presence of several metal ions. To investigate the sensor analytical applicability, it was tested as an indicator electrode in the potentiometric titration of Yb(III) solution with standard EDTA solution. The proposed electrode was also used to determine fluoride ions in mouthwash.     

Mercury-selective membrane electrode based on methyl substituted dibenzo tetraphenyl tetraaza macrocycle

A new polystyrene based membrane electrode of methyl substituted 6,7:13,14-dibenzo-2,4,9,11-tetraphenyl-1,5,8,12-tetraazacyclotetradeca-1,4,6,8,11,13-hexaene (I) with sodium tetraphenylborate (NaTPB) and dibutyl phthalate (DBP) as anion excluder and plasticizing agent was prepared and investigated as Hg (II)-selective electrode. The electrode exhibits a Nernstian response for Hg (II) ions over a wide concentration range of 1.0 × 10⁻¹–8.9 × 10⁻⁶ M with a slope of 30 ± 1 mV per decade concentration. It has a response time of 10 s and can be used for at least 4 months without any divergence in potentials. The membrane works satisfactorily in a partially non-aqueous medium up to a maximum 30% (v/v) content of methanol and ethanol. The proposed sensor revealed good selectivity over a wide variety of other cations including alkali, alkaline earth, heavy and transition metal ions and could be used in a pH range of 2.5–5.0. Normal interferents like Ag⁺, Cd²⁺ and Pb²⁺ low interfere in the working of the electrode. The electrode was successfully used in the direct determination of Hg²⁺ in aqueous solution.     

Linear scan stripping voltammetry of copper(II) at the chemically modified carbon paste electrode

A new chemically modified electrode (CME), -benzoinoxime (CUPRON) modified carbon paste electrode, for determining copper(II) is reported because of its excellent selectivity and sensitivity. The electrode is made by mixing a quantity of CUPRON (25%, w/w) with graphite powder (50%, w/w) and paraffin oil (25%, w/w). The CME preferentially deposits copper from the pH 8.5 NH₃-NH₄Cl buffer solution containing copper(II) under an open circuit and most of metal ions do not interfere with the measurements. The detection limit (S/N of three) for determining Cu(II) is 3 × 10^–10 g/ml after 10 min accumulation in fast linear scan stripping voltammetric measurement. Linear calibration curves are obtained for Cu(II) concentration ranged from 1 × 10^–8 M to 1 × 10^–6 M. The response can be maintained with relative standard deviation of 6.0% in a 5 × 10^–6 M Cu(II) solution after eight accumulation/measurement/ regeneration cycles at the same electrode surface. The effect resulted from carbon paste preparation, reduction potential, electrode renewal, electrolyte and solution pH, preconcentration time, concentration dependence, possible interference and other variables has been evaluated. As for application, the CME demonstrates its high sensitivity and copper-selectivity in complex composition samples, such as anodic mud and polluted water.     

Synthesis of <Emphasis Type="Italic">N</Emphasis>-Tosylates of 4-Methoxy-1,2,3,4-tetrahydrocarbazole and 2-(6-Methoxy-1-cycloalken-1-yl)anilines

The reaction of N-tosylates of 2-(1-cycloalken-1-yl)anilines and 2,3,9a,9-tetrahydro-1H-carbazole with methanol in the presence of CuBr₂ proceeds with high regioselectivity leading to the corresponding tosylates of 2-(6-methoxy-1-cycloalken-1-yl)anilines and 4-methoxy-1,2,3,4-tetrahydrocarbazole. The latter as well as N-mesyl-1,2,3,4-tetrahydrocarbazole showed moderate cytotoxic activity with respect to HEK293 cell line.     

Papaverine-Selective Plastic Membrane Electrode Based on Papaverinium Tetraphenylborate

Abstract

A plasticized PVC membrane containing the lipophilic salt papaverinium-tetraphenylborate was used to construct an ion-selective electrode for papaverine hydrochloride (Pv⁺Cl^?). The electrode shows near Nernstian response over the concentration range 1.6 × 10^?5 1.3C × 10^?2M PvCl in solutions of pH 1.0–6.2 at 25[ddot]C. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode. The electrode showed very good selectivity for Pv with respect to a large number of inorganic and organic cations. The potentiometric titration and standard addition methods were used to determine Pv in pure solutions and in pharmaceutical preparations.     

Determination of Titanium In Quartz and Silica Glass Samples By Adsorptive Stripping voltammetry

ABSTRACT

This article presents a method for determination of titanium in quartz and silica glass samples based on adsorptive stripping voltammetry (AdSV) with mandelic acid. Hanging mercury drop electrode as a working electrode was used. The optimized conditions include: pH 3.3, accumulation potential –0.15 V, accumulation time 90 s, scan rate 10 mV/s, pulse amplitude 25 mV. In case of 5 min accumulation time the obtained detection limit was 6.5×10^-9 mol/L Ti. ET-AAS was applied as a reference method to AdSV measurements. The procedure for decomposition of quartz and silica glass samples applying small amount of acids is described.     

Preconcentration and differential pulse voltammetry of butylated hydroxyanisole at a carbon paste electrode

Butylated hydroxyanisole (BHA) and other tocopherols are shown to accumulate very strongly onto carbon paste, with the surface species retaining their characteristic electroactivity. This accumulation serves as a preconcentration step which improves the voltammetric measurement with respect to the sensitivity and selectivity. After 5-min preconcentration, a detection limit near 2 × 10^?8 M BHA is obtained. Enhanced selectivity is achieved if the electrode is transferred into an electrolytic blank solution between the preconcentration and measurement steps. The accumulated analyte can then be quantified in the presence of a 10³-fold amount of a solution species with similar redox potential. The differential pulse stripping response is evaluated with respect to concentration dependence, reproducibility, preconcentration period, detection limit, and other variables. The preconcentration/medium exchange approach is exploited for selective detection of BHA in a flow injection system. Applicability to various real samples is illustrated.     

Determination of L-Ascorbic Acid by Adsorption Potentiometry with Carbon Paste Electrode

Abstract

This paper reports the potentiometric measurement of ascorbic acid in the solution of 0.10 mol/L NaOH-0.1 mol/L NaCl using carbon paste (the mixture of spectroscopic graphite powder and di-iso-octyl phthalate) electrode(room temperature 15°C), with the linear range 7.0 × 10^?7 × 4.0 × 10^?5mol/L, average response slope 95mV/decade and detection limit 1 × 10^?7mol/L. Phenol, sulfite, Mn²⁺ and so on pose no interference to the measurement of ascorbic acid. This method is characterized by fine selectivity, reproducibility and accuracy. The potential response behavior is caused chiefly by chemisorption of ascorbic acid to the surface of the carbon.

Each year yields a number of papers concerning the determination of ascorbic acid by various methods, including gas chromatographymass spectrometry¹, capillary electrophoresis², spectrophotometry³, voltammetry⁴, titrimetric method⁵, biosensor⁶ and so on, Each method has its merits and defects in analyzing different samples. M. Petersson⁷ worked out the potentiometric sensor for determining ascorbic acid by modifying monolayer of ferrocene upon the surface of half-oxidized platinum electrode with an average response slope 50±8.8mV/decade, but this sensor suffers from inadequate selectivity. In our study, carbon paste electrode (without ionophore) is applied in the determination of ascorbic acid by potentiometry with an average response slope 95mV/decade. This method displays fine selectivity, accuracy, convenience and rapidity of determination.     

Thallium(I) Selective Solid Membrane Electrode

Abstract

Heterogeneous membranes of 2.0 cm diameter were prepared from a 60:40 mixture of thallium(I) molybdoarsenate and Araldite, These membranes gave near Nernstian response to thallium(I) ions over the concentration range 10^?1 to 10^?3M but could be used for determination of thallium(I) down to 10^?5M. Slope of the log concentration-potential plot is improved in 10 and 25 percent acetone-water mixture. The response was independent of pH over the range 4.0 to 6.0, The response time of the electrode is few seconds and potentials generated are reproducible. The selectivity of the electrode over a large number of cations was studied. The values of selectivity coefficients are of the order 10^?2 for monovalent and 10^?3 for bivalent cations. Anions did not interfere. Potentiometric-titration of thallium nitrate with potassium chromate was also done using the membrane as an end point indicator electrode.