Electrochemical oxidation of 8-hydroxyquinoline and selective determination of tin(II) at solid electrodes

The electrochemical oxidation of 8-hydroxyquinoline and several structurally related molecules has been investigated by cyclic voltammetry at solid electrodes (GCE, CPE, Pt) as a function of pH in aqueous acetate media. Oxine showed one irreversible oxidation peak whose magnitude decreased in the presence of cations readily complexed by oxine and with concomitent formation of a new oxidation peak at more positive potentials. Tin(II ) was found to exhibit a distinct behavior as its oxidation was catalyzed by the presence of oxine in the analyzed solution. The tin(II )-oxine oxidation peak was found to be linearly related to inorganic tin(II ) concentration allowing its quantitative determination at micromolar levels.     

Modified solid electrodes for stripping voltammetric determination of tin

The paper describes the determination of tin by ASV using modified thick film electrodes. Three different types of electrodes were developed: One modified with a mixture of Nafion and mercury(II)acetate, one modified with diethyldithiocarbamate (DDC) or pyrrolidinedithiocarbamate (PDC) and mercury(II)acetate, and one modified with calomel. The analyte was accumulated on the electrode surface after special electrochemical pretreatment of the modified electrode. After recording the voltammogram the electrodes were electrochemically regenerated. By virtue of their lifetime and their measurement reproducibility, we preferred the DDC and PDC modified electrodes. They can be used for months without changing their chemical characteristics. The linear range for tin determination with these electrodes is between 1 and 100 μg/L; the detection limit was calculated as 0.9 μg/L. The electrodes were applied to the direct determination of tin in different canned fruit juices without special sample pretreatment. Received: 20 December 1996 / Revised: 11 March 1997 / Accepted: 13 March 1997     

Modified solid electrodes for stripping voltammetric determination of tin

The paper describes the determination of tin by ASV using modified thick film electrodes. Three different types of electrodes were developed: One modified with a mixture of Nafion and mercury(II)acetate, one modified with diethyldithiocarbamate (DDC) or pyrrolidinedithiocarbamate (PDC) and mercury(II)acetate, and one modified with calomel. The analyte was accumulated on the electrode surface after special electrochemical pretreatment of the modified electrode. After recording the voltammogram the electrodes were electrochemically regenerated. By virtue of their lifetime and their measurement reproducibility, we preferred the DDC and PDC modified electrodes. They can be used for months without changing their chemical characteristics. The linear range for tin determination with these electrodes is between 1 and 100 μg/L; the detection limit was calculated as 0.9 μg/L. The electrodes were applied to the direct determination of tin in different canned fruit juices without special sample pretreatment. Received: 20 December 1996 / Revised: 11 March 1997 / Accepted: 13 March 1997     

Modified Glassy-Carbon Electrodes for the Flow-Injection Determination of Inorganic Tin Species by Stripping Voltammetry

The behavior of tin(II, IV) chloride species on an unmodified glassy-carbon electrode, and on or at film electrodes obtained by the electrooxidative modification of a glassy-carbon surface, in solutions of some polyphenols and other hydroxyl-containing aromatic compounds (salicylic acid and morin) was studied by cyclic voltammetry. The optimum conditions were found for the potentiostatic formation of films reproducible in thickness in the cyclic hydrodynamic mode. A comparison of the results of the studies demonstrated the effect of hydrophobic film nature on the redox processes observed in Sn(II, IV) and Pb(II) chloride solutions at different pHs. All the electrodes proposed preconcentrated tin(II) from flow solutions without applying a polarization voltage. The interfering effect of lead(II) was minimized by selecting an appropriate accumulation medium. The modified electrodes prepared by the electrooxidation of pyrogallol and morin were used for the flow-injection determination of trace amounts of Sn(II) in the presence of Sn(IV) and Pb(II) and for the determination of the total inorganic tin in model solutions by anodic stripping voltammetry.     

Electrochemical determination of some antidiabetic drugs for type 2 diabetic patients

Quantitative determination of rosiglitazone, pioglitazone, glimepiride and glyburide as antidiabetic drugs for type 2 diabetic patients was performed conveniently and economically using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Carbon paste (CPE) and glassy carbon (GCE) electrodes were successfully used as sensors for these drugs in Briton-Robinson (B-R) as buffer solution. The preparation of CPE and the GCE as ion selective electrodes is based on the construction of 10% standard drug ion pair with reineckate or tungstophosphate imbedded as electroactive material. Working standards were freshly prepared just before the assay by dilution from a 10⁻² mol L⁻¹ drug stock solution. At a scan rate of 100 mV s⁻¹ the cyclic voltammograms showed a well defined anodic peak with high selectivity. The DVP gave a reproducible well defined diffusion controlled peak for each drug at a scan rate of 10 mV s⁻¹. The oxidation peaks were used to determine the tested drug concentrations. The quantitative determination of the four drugs in their pharmaceutical preparations by the proposed electrochemical technique was found to be identical with the values obtained by the standard HPLC method. A mean % recovery of 100 ± 1 was obtained and the % relative standard deviation was 1.62 indicating the high precision of the method and the confidence in its repeatability. The proposed electroanalytical technique using either the CPE or the GCE is economic, selective and can be applied for both the qualitative and quantitative determination of the drugs in their pharmaceutical preparations, without special drug separation.     

Simultaneous Voltammetric Determination of Lead and Tin by Adsorptive Differential Pulse Stripping Method and Orthogonal Signal Correction‐Partial Least Squares in Water Samples

An adsorptive differential pulse stripping method for the simultaneous determination of lead and tin is proposed. The procedure involves an adsorptive accumulation of lead and tin on a hanging mercury drop electrode (HMDE), followed by oxidation of adsorbed lead and tin by voltammetric scan using differential pulse modulation. The optimum experimental conditions are: 0.2 mol L^?1 HNO₃, accumulation potential of ?900 mV versus Ag/AgCl, accumulation time of 200 s, scan rate of 20 mV s^?1 and pulse height of 80 mV. Lead and tin peak currents were observed in the same potential region at about ?400 mV. The simultaneous determination of lead and tin by using voltammetry is a difficult problem in analytical chemistry, due to voltammogram interferences. The resolution of a mixture of lead and tin by the application of orthogonal signal correction‐partial least squares (OSC‐PLS) was performed. The linear dynamic ranges were 0.003‐0.35 and 0.008‐0.50 μg mL^?1 and detection limits were land 3 ng mL^?1 for lead and tin, respectively. The RMSEP for lead and tin with OSC and without OSC were 2.8737, 6.0557 and 8.0941, 9.5151, respectively. The capability of the method for the analysis of real samples was evaluated by the determination of lead and tin in water samples with satisfactory results.     

Fast and Simple Electroanalytical Identification of Iron Oxides in Geological Samples Without Sample Pretreatment

Hematite, goethite and siderite were found in geological samples using a simple, fast and low cost electroanalytical technique called voltammetry of immobilized microparticles (VMP). A carbon paste electrode was carefully rubbed onto the studied samples (an iron ore and ferrous oolites) to attach some microparticles to the surface of the electrode, and subsequently a potential scan was performed in two aqueous media to obtain the voltammogram which might be considered as the fingerprint of the sample deposited on the electrode. Each peak was related to an electrode process on the electrode whose peak potential indicates the type of iron compound. All the results were confirmed by commonly used analytical techniques to detect the presence of the different phases. All of this makes VMP an analytical tool very useful to save time and reduce analysis costs for geologist.     

Characteristics of Subtractive Anodic Stripping Voltammetry of Lead,Cadmium and Thallium at Silver‐Gold Alloy Electrodes

Silver‐gold alloy electrodes have been studied for the purpose of the quantitative determination of heavy metals by subtractive anodic stripping voltammetry, (SASV). The results have been compared with those obtained with the silver and gold electrodes. The 50/50 a/o Ag/Au alloy electrode is the most suitable for quantifying thallium in the presence of lead and cadmium. The separation of its peak from those of lead and cadmium is 200 mV, which is about twice the separation obtained on the pure metal electrodes and is also better than on mercury. The silver electrode is suitable for the simultaneous determination of thallium, lead and cadmium. The peaks of lead and cadmium overlap on the 50/50 alloy. Pure silver or pure gold can be used for simultaneous quantification of these two metals. The use of gold for quantifying lead and cadmium is more limited because the peak potential of cadmium is shifted in the negative direction as its concentration increases and at [Cd²⁺]>200 nM, the two peaks merge. SASV enables correction for background currents and is of utmost importance for obtaining well‐defined peaks. The peaks of lead, cadmium and thallium appear over a relatively narrow potential range (ca. 200 mV) on all the electrodes presented in this work. For this reason, the quantifying of a peak is based on the derivative at the inflection point of only one of its branches (ascending or descending). All SASV measurements were carried out without removal of oxygen.     

X射线荧光光谱法快速测定黑铜中的铜、砷、锑、铋、铅、镍、锌和锡

建立X射线荧光光谱法快速测定黑铜中的铜,砷,锑,铋,铅,镍,锌和锡等多种元素含量的方法。采用自制的黑铜样品作为标准样品建立标准工作曲线。实验确定了样品加工时最佳的铣样速度及谱线重叠干扰的校正方法,并用理论影响系数校正基体干扰。试验结果表明,各元素的工作曲线线性关系较好,线性相关系数均大于0.996。各元素的检出限在17~47μg/g之间。测定结果的相对标准偏差为0.038%~2.73%(n=7)。两个样品的测定结果与标准分析方法的测定结果相符。该方法具有较好的准确度和精密度,分析速度快,能满足炉前快速分析的需要。     

The determination of traces of antimony,tin and arsenic in cadmium by pulse polarography

Traces of antimony, tin and arsenic in cadmium products were determined by pulse polarography. Arsenic was distilled, while antimony and tin were precipitated as hydroxides with manganese dioxide as carrier; some lead was coprecipitated with tin, hence these elements were further separated by distillation. In all cases quantitative recoveries were obtained. Antimony(III) was determined in a hydrochloric acid-sodium hypophosphite mixture, tin(IV) in a hydrochloric-hydrobromic acid mixture and arsenic(III) in sulphuric acid as supporting electrolytes; for arsenic(III), methylene blue had to be added. A sample weight of 10 g and an end volume of 10 ml allowed the determination down to about 0.004 p.p.m. antimony, 0.006 p.p.m. tin and 0.003 p.p.m. arsenic in cadmium. Several synthetic samples and commercially available cadmium products were analysed.     

Preparation of lead and tin oxide thin films by spin coating and their application on the electrodegradation of organic pollutants

In this work, lead and tin oxide films (Pb _x O _y /SnO₂) were prepared, using the spin coating technique. The influence of the temperature and duration of the thermal treatment on the final film composition were analysed. The metallic oxide films that were prepared, Pb _x O _y /SnO₂, were characterized by means of XRD, SEM/EDS and cyclic voltammetry. When different experimental preparation conditions were used different lead oxide phases were obtained. The electrochemical studies show that the films are stable and can be used as electrodes. Finally the films were tested as electrodes for the electrochemical degradation of a CHCl₃ aqueous solution.     

Effects of casting temperature of Pb-Sb-Sn grid alloy on the polarization potential of oxygen evolution of lead acid batteries

The electrochemical polarization potential of oxygen evolution at the surface of lead-antimony-tin alloy is varied in different casting temperature of electrode production, which is used in the most of battery manufacturer. Effect of the casting temperature on the polarization potential of oxygen evolution and electrochemical behavior of lead-antimony-tin alloy in low antimony grid (1.7%) of lead acid battery is studied by using cyclic voltammetry and linear sweep voltammetry in aqueous sulfuric acid solution. The grid morphology is studied by using scanning electron microscopy and optical microscopy at the different casting temperatures. Cyclic voltammograms of the Pb-Sb-Sn and lead-antimony electrodes are similar, and both alloys show the anodic excursion peak under the same experimental conditions. The oxidation of tin is done at the formation potential of PbO. The results show the polarization potential for oxygen gas evolution to vary with casting temperature for production of lead-antimony electrodes. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 4, pp. 401–405. The text was submitted by the author in English.     

Identification of iron(III) oxides and hydroxy-oxides by voltammetry of immobilised microparticles

In this paper, we propose the use of an electroanalytical technique based on the direct oxidation or reduction of the electroactive components of the sample on the surface of the working electrode, called voltammetry of immobilised microparticles (VMPs). The sample is easily deposited on the electrode by abrasion and then the electrode is transferred to the electrochemical cell where the square wave potential scan is performed. Electroactive species showed peaks whose peak potential is related to the standard formal potentials. We applied this technique to the identification of iron oxides and hydroxy-oxides in cosmetics. To characterise and identify the iron(III) oxides and hydroxy-oxides VMP was performed in two different media: oxalic acid and hydrochloric acid, that is, a complexing and a slightly complexing media. Two electrode processes were observed. They were influenced by the media and the synthesis procedure of the oxides. The reduction peak at negative potentials (−0.50 V in hydrochloric acid and −0.60 V in oxalic acid) is related to the direct reduction of the iron(III) oxide and it does not appear in the case of the more reactive phases (hydroxy-oxides). The peak at positive potentials (0.90 V in hydrochloric acid and 0.60 V in oxalic acid) involves the reduction of iron(III) in solution. The same electrode process were observed for binary mixtures but the peak potentials are shifted from the pure components peak potentials. This allowed us to distinguish between their mixtures. Finally, VMP was used to characterise iron oxides in cosmetic powders.     

Simultaneous determination of four heavy metal ions in tobacco and tobacco additive by online enrichment followed by RP-HPLC and microwave digestion

A new method for the simultaneous determination of tin, lead, cadmium, and mercury in tobacco and tobacco additive by reversed-phase high-performance liquid chromatography combined with microwave digestion and an online enrichment technique is developed. The tin, lead, cadmium, and mercury ions are precolumn derivatized with tetra-(4-dimethylaminophenyl)-porphyrin (T(4)-DMAPP) to form color chelates. The Sn-T(4)-DMAPP, Hg-T(4)-DMAPP, Cd-T(4)-DMAPP, and Pb-T(4)-DMAPP chelates are absorbed onto the front of the enrichment column using a buffer solution of 0.05 mol/L pyrrolidine-acetic acid (pH = 10.0) as the mobile phase. After the concentration is finished (by switching the six-port switching valve) the retained chelates are back-flushed by the mobile phase and move to the analytical column. The chelate separation on the analytical column is satisfactory using gradient elution with methanol (containing 0.05 mol/L pyrrolidine-acetic acid buffer salt, pH = 10.0) and tetrahydrofuran (containing 0.05 mol/L pyrrolidine-acetic acid buffer salt, pH = 10.0). The linearity range is 0.01-120 micro g/L for each metal ion. The detection limits (S/N = 3) of tin, lead, cadmium, and mercury are 0.6, 0.8, 0.5, and 0.6 ng/L, respectively. This method is applied to the determination of tin, lead, cadmium, and mercury in tobacco and it's additive with good results.     

Electroanalysis of Norepinephrine at Bare Gold Electrode Pure and Modified with Gold Nanoparticles and S‐Functionalized Self‐Assembled Layers in Aqueous Solution. Part II

Gold electrodes modified with S‐containing compounds and gold were used for determination of norepinephrine (NEP) in aqueous solution. A linear relationship between norepinephrine concentration and current response was obtained in the range of 0.1 µM to 600 µM with the detection limit ≤0.090 µM for the electrodes modified at 2D template and in the range of 0.1 µM to 700 µM with the detection limit ≤0.075 µM for the electrodes modified at 3D template. The results have shown that modified electrodes could clearly resolve the oxidation peaks of norepinephrine, ascorbic (AA) and uric acid (UA) with peak‐to‐peak separation enabling determination of NEP, AA and UA in the presence of each other.     

Sensitive Anodic Stripping Voltammetric Copper Ions Determination Performed in Double Deposition and Double Stripping Steps System for Real Water Samples Analysis

The article reports on utilization of double deposition and stripping steps for increasing sensitivity of Cu(II) determination by anodic stripping voltammetry (ASV) at two lead film working electrodes. A significant preconcentration of copper was achieved thanks to utilization of a simple design of four electrodes system that gives possibility to perform one measurement cycle consisting of two deposition and two stripping steps. Due to the fact that deposition step is doubled, the concentration of Pb(II) needed to lead film electrodes formation was significantly reduced as compared to traditional procedures using three electrodes system. The analytical procedure of Cu(II) determination was optimized. The experimental factors: supporting electrolyte's pH and its concentration, lead ions concentration, potential and time of deposition at both working electrodes were studied. The Cu(II) peak current was linearly dependent on its concentration from 5×10^?10 to 2×10^?8 mol L^?1 (deposition time of 270 and 160 s at the first and the second working electrode, respectively). The obtained detection limit for copper ions determination was 2.1×10^?10 mol L^?1. The described procedure was validated by analysis of two water certified reference materials. The described procedure was also utilized for real water sample analysis.     

Cyclic and stripping voltammetry of tin at mercury hanging drop and film electrodes in acidic o-diphenol media in the presence of lead and cadmium

The influence of catechol, gallic acid and tiron on the voltammetric behaviour of tin(IV) in the presence of lead(II) and cadmium(II) was investigated at hanging drop and mercury film electrodes in perchloric acid, oxalic acid and formate supporting electrolytes. Under cyclic conditions, well separated peaks of tin, lead and cadmium are obtained in oxalic acid and formate solutions containing gallic acid or catechol; tiron suppresses the tin peaks significantly. The efficiency of the deposition of tin in the presence of catechol or gallic acid is less than that of lead, particularly at long deposition time. The best separation of the stripping peaks of tin, lead and cadmium is obtained in oxalic acid solution containing gallic acid or catechol. In perchloric acid solution containing gallic acid or catechol the second peak corresponding to tin oxidation is useful for determinations of tin in the presence of lead. Tin(IV) at the 10^-8 mol l^-1 level can be detemined in various salt solutions and in water samples in the presence of five-fold amounts of lead and cadmium.     

Flow analysis-hydride generation-Fourier transform infrared spectrometry. A new analytical technique for the simultaneous determination of antimony,arsenic and tin

The combination of flow analysis (FA), hydride generation (HG) and Fourier transform infrared (FTIR) spectrometry is proposed as a novel and powerful analytical technique for the individual and simultaneous determination of antimony, arsenic and tin in aqueous samples. The analytes were transformed into the volatile hydride form by on-line reaction with sodium tetrahydroborate in acidic medium. The gaseous analyte hydrides [M(n)H(m), (g)] generated, were transported by means of a carrier gas stream inside the IR gas cell and the corresponding FTIR spectrum was acquired in a continuous mode. The 1893, 1904 and 2115 cm(-1) bands of the SbH3, SnH4, and AsH3 were selected for the determination of antimony, tin and arsenic, respectively. The limit of detection (3sigma) obtained by using a short-path (10 cm) IR gas cell were 0.25, 0.30 and 1.2 mg l(-1) for the determination of antimony, tin and arsenic, respectively; while the precision (relative standard deviation, RSD, n 5) found from a standard solution containing 50 mg l(-1) of each element was, in all cases, less than 0.3%. However, the use of a long-path (7.25 m) IR gas cell improved the figures of merit (sensitivity, limits of detection and quantification) nearly 60-fold. The effect of the main experimental and instrumental variables, such as acidic media, sodium tetraborohydrate concentration, nitrogen flow rate, nominal resolution and the scan accumulation on the analytical signals of the antimony, tin and arsenic hydrides, were studied. Further, the potential of the proposed technique for the simultaneous determination of these elements was tested, analyzing synthetic samples containing different amounts of Sb, Sn and As.     

Fabrication of Nano Flower‐shaped Platinum on Glassy Carbon Electrode as a Sensitive Sensor for Lead Electrochemical Analysis

Platinum nanoflowers modified glassy carbon electrodes (PtNFs/GCE) was fabricated simply for lead determination in water samples. The modified electrodes were prepared by electrodeposition in hexachloroplatinic acid solution at constant potential. The influence of deposition time and potential on surface morphology, chemical composition, electrochemical properties of electrode were investigated. At ?0.2 V of potential and 150 s of deposition duration, platinum developed as nanoflower shape and scattered densely all over the glassy carbon surface, producing the largest electrochemically active surface areas. The highest differential pulse stripping voltammetry (DPSV) signal of lead was obtained by using the prepared electrode. Under optimized experimental condition of electrolyte, accumulation potential and time, the peak current was found to be linear proportion to lead concentration in range of 1 to 100 μg L^?1 (slope=0.371) with a limit of detection of 0.398 μg L^?1. The method has good repeatability and reproducibility with relative standard deviations of 1.47 % and 4.83 %, respectively. The modified PtNFs/GCE also demonstrated an excellent long‐term stability with only 9 % decrease in Pb peak current over 30 days. Moreover, the performance of the modified PtNFs/GCE in determination of Pb(II) in two industrial wastewaters was good agreement with data obtained by a graphite furnace atomic absorption spectrometry (GFAAS) method.     

Studies on the coulometric determination of uranium and plutonium employing a graphite electrode

Summary Graphite has been employed as a working electrode in the controlled potential coulometric determination of uranium and plutonium. The couples U(VI)/U(IV) and Pu(IV)/Pu(III) employed for analysis have diverse redox potentials and commonly the working electrodes employed are mercury and platinum. A graphite electrode in the shape of a beaker showed satisfactory performance for the quantitative reduction of U(VI) to U(IV) and Pu(IV) to Pu(III) and also for quantitative oxidation of Pu(III) to Pu(IV). Studies on the levels of the background current, blank values and their reproducible behaviour in acid media have been carried out with a view to achieve good precision and accuracy. A software-based predictive evaluation technique of end-point charge has been investigated. The results have shown that the graphite electrode can be used for the determination of both uranium and plutonium in the presence of each other with a precision and accuracy of better than ±0.5%.