Electrochemical Determination of Methyltin Compounds

 The electrochemical behaviour of monomethyltin, dimethyltin and trimethyltin compounds in 20% (V/V) methanol/water solution, 0.05 mol/L in tetraethylammonium perchlorate at pH 2.5, has been investigated by differential pulse polarography and differential pulse anodic stripping voltammetry. In differential pulse polarography, dimethyltin and trimethyltin gave one reversible wave with peak potentials at −0.70 V and −1.07 V, respectively. Detection limits were 6.6 × 10⁻⁷ mol/L for dimethyltin and 4.1 ×  10⁻⁶ mol/L for trimethyltin. The electrochemistry of monomethyltin was found to be more complex. By differential pulse anodic stripping voltammetry, monomethyltin, dimethyltin and trimethyltin produced distinct stripping peaks (−0.39 V, −0.75 V and −1.14 V, respectively), which allow to determine these compounds at trace levels. Using this new method, detection limits were: 1.2 × 10⁻⁷ mol/L for monomethyltin, 1.7 × 10⁻⁷ mol/L for dimethyltin and 1.4 × 10⁻⁶ mol/ L for trimethyltin. For monomethyltin, a second peak (E_p = −0.60 V), less sensitive (detection limit of 2.5 × 10⁻⁶ mol/L), was also observed at concentrations above 4.2 × 10⁻⁷ mol/L. Recoveries of methyltin compounds added separately to tap water samples at the 0.42–16.9 μmol per litre level ranged from 84.5 to 99.8% depending upon the methyltin species. Received January 3, 2001. Revision August 10, 2001.     

DPASV Method for Determination of Trace Concentrations of Manganese in Non-Buffered Chloride Solutions by Addition of Cyanide as a Masking Agent

 A highly sensitive, selective, and rapid differential pulse anodic stripping voltammetric method at HMDE is described for the determination of trace concentrations of Mn²⁺. The determination of Mn²⁺ in non-buffered chloride solution is seriously disturbed by the presence of Ni²⁺, Co²⁺, Cr³⁺, Zn²⁺ and Cu²⁺ due to intermetallic compound formation. The procedure is based on the addition of low amounts of cyanide as a masking agent. The interference of < 20 μgL⁻¹ of Ni²⁺, Co²⁺ and Cr³⁺ and < 75 μgL⁻¹ of Cu²⁺ and Zn²⁺ can thus be avoided, as the formed cyanide complexes prevent intermetallic compound formation during the short accumulation period. Thus, the addition of cyanide greatly improves the DPASV determination of manganese in non-buffered medium. A comparison between the determination of Mn²⁺ in the presence of a mixed cyanide/non-buffered chloride and in the ammoniacal buffer solution shows that the peak current of manganese in the presence of cyanide is four times higher with the same peak potential. The proposed method is shown to be applicable for the Mn²⁺ determination in both ground and tap water. A good agreement is obtained between the results by DPASV and AAS. Received May 14, 1999. Revision May 25, 2000.     

Determination of Amitraz Pesticide by Adsorptive Stripping Voltammetry on the Hanging Mercury Drop Electrode

 A sensitive method for the determination of amitraz pesticide at nanomolar level by adsorptive stripping voltammetry at a hanging mercury drop electrode is described. The cyclic voltammograms demonstrate the adsorption of this compound on the mercury electrode. A systematic study of the various experimental parameters, that affect the stripping response, was carried out by differential pulse voltammetry. Using an accumulation potential of −0.50 V, and 30 s accumulation time, the limit of detection was found to be 2.3 × 10⁻⁹ mol L⁻¹ and the relative standard deviations (n = 5) was 2.2% at concentration level of 5.0 × 10⁻⁸ mol L⁻¹ of amitraz. The influence of diverse ions and some other pesticides was investigated. Finally, the method was applied to the determination of amitraz in spiked soil and water. The relative standard deviation is 4.5% for 5 determinations of amitraz in water and 3.2% for 5 determinations in soil. Received December 6, 2000. Revision March 1, 2001.     

Novel,Sensitive Voltammetric Methods for Titanium Determination Using Chromotropic Acid and Azo‐Compounds as Complexing Agents

Voltammetric behavior of titanium(IV) complexes with chromotropic acid, its azo‐derivatives: 2‐(4‐sulfophenylazo)‐1,8‐dihydroxy‐3,6‐naphthalenedisulfonic acid (SPANDS), chromotrope 2B, sulfonazo III and other azo‐compounds: calmagite, tropeoline O and kalces was investigated at a hanging mercury drop electrode. These complexes strongly adsorb onto the electrode, thus can be determined by an adsorptive stripping voltammetry (optimal pH about 6). At pH about 3 reduction current enhancement for Ti‐kalces complex was observed in the presence of chlorate ions. It is a rare example of a catalytic process with azo‐compound as a complexing agent. Signal for Fe‐calmagite complex reduction was also observed. Influence of foreign ions and the optimal conditions for titanium determination are described in detail. Additionally, a connection between obtained results and a structure of titanium complexes is discussed.     

Preconcentration and Voltammetric Study of Nicergoline at a Carbon Paste Electrode

 The electrochemical oxidation of nicergoline is investigated using cyclic and differential pulse voltammetry at a carbon paste electrode. For the determination of nicergoline an adsorptive stripping procedure is proposed. The response is characterized with respect to pH, ionic strength, preconcentration time, accumulation potential, nicergoline concentration, reproducibility and other variables. By differential pulse voltammetry at a carbon paste electrode and pH 8.0, a linear calibration in the range 5×10⁻⁸ M to 1×10⁻⁷ M and a detection limit of 1×10⁻⁸ M are obtained. The preconcentration medium-exchange approach was used for a selective determination of nicergoline in urine. For dilute urine samples a detection limit of 5×10⁻⁸ M is obtained after 3 min of accumulation and medium-exchange. The procedure also is applied for the determination of nicergoline in dosage form. Received August 24, 1998. Revision April 8, 1999.     

Determination of Trace Manganese by Adsorption Voltammetry

Abstract

In a solution containing 0.005M borax medium (PH= 8? 10). 0.03% ascorbic acid and 0.001% gelatin, a fine sensitive adsorptive reduction peak of manganese appeared at ?1.53v (vs.SCE) on a hanging mercury electrode by fast speed scanning voltammetry. The derivative peak current is directly proportional to the concentration of manganese in the range from 1.0×10^?8M to 2.0×10^?6M. The detection limit is 3.0×10^?9M. Using this method, we have successfuly determined tracesof Mn in water and strawberry samples.     

精氨酸在苯甲醛存在下的吸附溶出伏安法研究

在０．２ｍｏｌ／ＬＮａＯＨ－０．０４ｍｏｌ／ＬＨ３ＰＯ４－０．０２ｍｏｌ／Ｌ（ＮＨ４）２ＳＯ４－０．０４ｍｏｌ／ＬＣＨ３ＣＯＯＨ溶液中，精氨酸（Ａｒｇ）在苯甲醛存在下产生一灵敏的吸附波。实验证明电活性物质为α－苯亚甲基精氨酸，其电极反应机理是分子内α－＞Ｃ＝Ｎ基团被还原为亚胺。用该吸附波可在１×１０（－３）～２×１０（－６）ｍｏｌ／Ｌ范围内分析蛋白质中的Ａｒｇ。     

A New Differential Pulse Voltammetric Method for the Determination of Nitrate at a Copper Plated Glassy Carbon Electrode

 A differential pulse voltammetric method for the determination of nitrate has been described, which is applicable to the analysis of natural water samples with nitrate levels greater than 2.8 × 10⁻⁶ M. A reduction peak for the nitrate ions at a freshly copper plated glassy carbon electrode was observed at about −0.50 V vs Ag ∣AgCl∣KCl_satd electrode in a solution of 2.0 × 10⁻² M Cu²⁺, 0.5 M H₂SO₄ and 1.0 × 10⁻³ M KCl and exploited for analytical purposes. The working linear range was established by regression analysis and found to extend from 2.8 ×10⁻⁶ M to 8.0 × 10⁻⁵ M. The proposed method was applied for the determination of nitrate in natural waters. The detection limit of the method was 2.8 × 10⁻⁶ M and the sensitivity was 0.9683 A·L/mol. The possible interferences by some ions such as phosphate, nitrite and some halides were determined and found to lead to shifts of the peak position and increasing the peak heights. Received March 15, 1999. Revision July 9, 1999.     

Simultaneous Determination of Antimony(III) and Molybdenum(VI) by Adsorptive Stripping Voltammetry Using Quercetin as Complexing Agent

A sensitive and selective voltammetric method for simultaneous determination of Sb(III) and Mo(VI) using Quercetin (Q) as complexing agent is described. Optimal conditions were found to be: pH 3.7, C_Q=6.0 µmol L^?1 and E_acc=?0.10 V. The LOD (3σ) for Sb(III) are 0.076 and 0.040 µg L^?1, whereas for Mo(VI) are 0.086 and 0.048 µg L^?1 with t_acc of 60 and 120 s, respectively. The method was validated using synthetic sea water (ASTM D665) and was applied to the determination of Sb(III) and Mo(VI) in natural waters with satisfactory results.     

Adsorptive Stripping Voltammetric Measurements of Trace Molybdenum at the Bismuth Film Electrode

Bismuth‐film electrodes on glassy‐carbon substrates have been successfully applied for adsorptive‐stripping voltammetric measurements of trace molybdenum in the presence of chloranilic acid (CAA). The procedure is based on the preconcentration of the molybdenum‐chloranilic acid complex at a preplated bismuth film electrode held at ?0.55 V (vs. Ag/AgCl), followed by a negatively‐sweeping square‐wave voltammetric scan. Factors influencing the adsorptive stripping performance, including different ligands, solution pH, CAA concentration, preconcentration time and potential, have been optimized. The response compares favorably with that observed at mercury film electrodes, and is linear over the 5–50 μg/L Mo concentration range (one min preconcentration). A detection limit of 0.2 μg/L molybdenum is obtained following a 10 min accumulation. High stability is indicated from the reproducible response of a 100 μg/L molybdenum solution (n= 60; RSD=2.6%). Applicability to seawater samples is demonstrated.     

Voltammetric Determination of Selected Aminoquinolines Using Carbon Paste Electrode

Optimum conditions have been found for voltammetric determination of mutagenic 5‐aminoquinoline, 6‐aminoquinoline and 3‐aminoquinoline by differential pulse voltammetry and adsorptive stripping differential pulse voltammetry on carbon paste electrode. The lowest limits of determination were found for adsorptive stripping differential pulse voltammetry in 0.1 mol dm^?3 H₃PO₄ (5×10^?7 mol dm^?3 , 1×10^?7 mol dm^?3, and 1×10^?7 mol dm^?3 for 5‐aminoquinoline, 6‐aminoquinoline and 3‐aminoquinoline, respectively). The possibility to determine mixtures of 8‐aminoquinoline with 3‐aminoquinoline or 5‐aminoquinoline or 6‐aminoquinoline, and mixtures of 5‐aminoquinoline with 3‐aminoquinoline or 6‐aminoquinoline by differential pulse voltammetry was verified. Binary mixtures of 8‐aminoquinoline with 3‐aminoquinoline or 6‐aminoquinoline, and of 3‐aminoquinoline with 5‐aminoquinoline could be successfully analyzed.     

Adsorptive Stripping Voltammetric Determination of Antimony by Using Alizarin Red S

Abstract

A sensitive and selective voltammetric method for determination of antimony(III) using Alizarin Red S (ARS) as complexing agent is described. The method is based on the monitoring the oxidation peak of antimony(III)-ARS complex at ?520 mV in ammonium-ammonia buffer (pH = 7.5). The peak current was measured by scanning the potential from ?700 mV versus Ag/AgClto more positive potentials without accumulation in the presence of 1 × 10^?6 mol L^?1 of ARS. The limit of detection (3 s) and limit of quantification (10 s) of the method were calculated from calibration curve as 1.45 µg L^? and 4.8 µg L^? respectively. The calibration plot for antimony(III) was linear in the range of 4.8–30 µg L^?. The interference of various ions was examined. Serious interference from Al(III), Fe(III), Cu(II), Pb(II), and Zn(II) was eliminated by addition of EDTA to the solution. The method was applied to drinking water samples. The recoveries were in the range 94% – 105%. The results obtained from the developed method were compared with those from the differential-pulse anodic-stripping method and no statistically significant difference was found.     

Preconcentration and Voltammetric Determination of the Antihypertensive Doxazosin on a C8 Modified Carbon Paste Electrode

 An electrochemical study of the doxazosin oxidative process at carbon paste electrodes using different voltammetric techniques has been carried out. The process is irreversible and controlled by adsorption, giving rise to an oxidation wave around 1.0 V in citric acid-citrate buffer (pH 3.0). A mechanism based on the oxidation of the amine group is postulated. Two methods based on adsorptive stripping (AdS) of doxazosin at the C₈-modified carbon paste electrode (C₈-MCPE), before its voltammetric determination, are studied, using differential pulse voltammetry (DPV) and square wave voltammetry (SWV) as redissolution techniques. By means of AdS-DPV and C₈-MCPE, doxazosin can be determined over the 1.0 × 10⁻⁹ to 3.0 × 10⁻⁸ mol L⁻¹ range with a variation coefficient of 2.2% (2.0 × 10⁻⁸ mol L⁻¹) and a limit of detection of 7.4 ×10⁻¹⁰ mol L⁻¹. If AdS-SWV is used, a linear range from 1.0 × 10⁻⁹ to 4.0 × 10⁻⁸ mol L⁻¹ is obtained, the variation coefficient being 2.8% (2.0 × 10⁻⁸ mol L⁻¹, and the limit of detection reached 7.7 × 10⁻¹⁰ mol L⁻¹. The AdS-DPV procedure was applied to the determination of doxazosin in urine and formulations. Received March 13, 1999. Revision December 23, 1999.     

分光光度法同时测定中草药中的钼和铜

本文建立了在混合显色剂（ＰＦ＋ＰＡＮ）的胶束体系中，利用分光光度法同时测定中草药中的钼和铜。实验表明：在混合体系中，钼量在０～１０μｇ／２５ｍＬ，铜量在０～５０μｇ／２５ｍＬ的范围内符合比尔定律，ε′Ｍｏ＝９．２×１０４Ｌ·ｍｏｌ－１·ｃｍ－１；ε′Ｃｎ＝１．５×１０４Ｌ·ｍｏｌ－１·ｃｍ－１。该法用于中草药样品的分析，结果满意，回收率可达９２～１１１％。     

吸附伏安法测定中草药中的钼

叙述了测定痕量钼的一种灵敏的吸附伏安法。本法以钼（Ⅵ）和茜素红络合物在悬汞电极上的吸附行为为基础，在０．０１ｍｏｌ／ＬＮａＡｃ、０．０８ｍｏｌ／ＬＨＡｃ和１．５×１０－６ｍｏｌ／Ｌ茜素红底液条件下，该体系１．５、２．５阶微分吸附伏安法的线性范围是７．５×１０－１１～７．５×１０８ｍｏｌ／Ｌ；对２．５阶微分吸附伏安法，富集３ｍｉｎ的检测下限是５×１０－１１ｍｏｌ／Ｌ。用此法直接测定了中草药中的痕量钼。     

米托蒽醌的吸附行为及其吸附伏安测定法研究

本文研究了米托蒽醌在悬汞电极上的吸附行为，在此基础上建立了米托蒽醌的吸附伏安测定方法。在ｐＨ为２．２的Ｂ．Ｒ缓冲体系中，米托蒽醌浓度在１．１×１０＾－６ｍｏｌ／Ｌ～１．１×１０＾－９ｍｏｌ／Ｌ范围内，浓度与电流呈线性，检出限可达５．５×１０＾－１０ｍｏｌ／Ｌ。若在盐酸－柠檬酸钠（ｐＨ为１．２５）缓冲体系中，检出限可低至１．１×１０＾－１１２ｍｏｌ／Ｌ。方法可用于尿样或血样中米托蒽醌的测定。     

Voltammetric and Spectrophotometric Determination of Nizatidi ne in Pharmaceutical Formulations

 Two methods are described for quantitative determination of nizatidine. The first is a cathodic stripping voltammetric method which is based on the accumulation of the compound at the hanging mercury drop electrode. The adsorptive stripping response was evaluated with respect of accumulation time, potential, concentration, pH and other variables. A linear calibration graph was obtained over the range 3.0×10⁻⁸–1.0×10⁻⁶ M with a detection limit 3.0×10⁻⁸ M after a 20s accumulation time at −0.2 V accumulation potential. On the other hand, it was found that the detection limit could be lowered to 1.0×10⁻⁸ M after 180s accumulation time at −0.2 V accumulation potential. The relative standard deviation was in the range 1.2−2.0% for six measurements. The tolerance amounts of the common excipients have also been reported. The second is a spectrophotometric method which is based on the formation and extraction of the ion-pair complex formed between nizatidine and either bromocresol green or bromothymol blue. The extracted colored ion-pair complexes absorb at 416 nm. The effect of different factors such as: type of organic solvent, pH, reagent concentration, number of extraction times, shaking time, temperature and the tolerance amount of the common excipients have been reported. The calibration graph was linear in the range 6.0×10⁻⁷–1.8×10⁻⁵ M with a detection limit of 6.0×10⁻⁷ M and molar absorptivity of 2.1×10⁴ lċmol⁻¹ċcm⁻¹ when using bromocresol green, while the calibration graph was linear in the range 3.0×10⁻⁷–1.1×10⁻⁵ M with a detection limit of 3.0×10⁻⁷ M and molar absorptivity of 3.2×10⁴ lċmol⁻¹ċcm⁻¹ when using bromothymol blue. The spectrophotometric methods offer alternative methods with reasonable sensitivity, selectivity and accuracy with relative standard deviation in the range 2.1−6.0% and 1.2−4.7% (for six measurements) when using bromothymol blue and bromocresol green, respectively. The proposed two methods were applied for the determination of nizatidine in commercially available dosage forms. A comparison between the voltammetric and the extraction-spectrophotometric methods was also reported. Received April 19, 1999. Revision August 30, 1999.     

Adsorptive Cathodic Stripping Voltammetric Method for Determination of Gallium Using an In Situ Plated Lead Film Electrode

The in situ plated lead film electrode was proposed for the first time for adsorptive stripping voltammetric determination of gallium in water samples. The method was based on simultaneous lead film formation and Ga(III)‐cupferron complex preconcentration at ?0.7 V and its cathodic stripping during the potential scan. The composition of the supporting electrolyte, cupferron concentration, conditions of lead film formation, potential and time of accumulation were studied in detail. Under optimum conditions the limit of detection was 3.8×10^?9 mol L^?1. The proposed procedure was validated in the course of Ga(III) determination in waste water certified reference materials.     

Multiwalled Carbon Nanotube Modified Electrodes for the Adsorptive Stripping Voltammetric Determination and Quantification of Curcumin in Turmeric

A sensitive electrochemical method for the determination and quantification of curcumin using adsorptive stripping voltammetry (AdsSV) at a multiwalled carbon nanotube modified basal plane pyrolytic graphite electrode (MWCNT‐BPPG electrode) is presented exploiting the high surface area of the latter. Next the voltammetric behaviour of curcumin on the modified electrode is examined and AdsSV shown to be a sensitive method for quantifying curcumin. The adsorption of curcumin on the electrode surface is evidenced to follow a Langmuir adsorption isotherm. Linear calibration for curcumin in the range of 2–100 μM was obtained with a detection limit of 0.45 μM and a limit of quantification of 1.49 μM. For application to real samples of turmeric, a one‐step sample preparation in ethanol has developed providing a simple and rapid extraction procedure. The MWCNT‐BPPG electrode with AdsSV allowed the determination of curcumin equivalent in turmeric powder sample with recoveries in the range of 92–108 %. This facile and fast method will be useful for monitoring the quality of curcumin containing in commercial turmeric products.     

Adsorptive Stripping Voltammetric Behavior of Probucole. Experimental and Theoretical Treatment

 Adsorptive stripping voltammetric behavior of probucole has been studied by means of cyclic staircase and square-wave voltammetry. It was found that the redox reaction of probucole in an aqueous medium exhibits properties of a surface process involving significant repulsion interactions between adsorbed molecules. A theoretical model was developed to explain the experimentally observed phenomena. Analytical application of the adsorptive stripping square-wave voltammetry for quantitative determination of probucole has been discussed. Received December 15, 2000. Revision June 20, 2001.