Simple and Highly Selective Catalytic Adsorptive Voltammetric Method for Cr(VI) Determination

A simple and highly selective and sensitive catalytic adsorptive stripping voltammetric procedure for determination of traces of Cr(VI) in the presence of a large excess of Cr(III) in environmental water samples is reported. To obtain a low detection limit the voltammetric procedure of chromium determination in the presence of DTPA and nitrate was exploited. For elimination of interference of Cr(III) ethylenediaminedisuccinic acid was used as a masking agent. At optimized conditions the calibration graph is linear from 2×10^?10 to 2×10^?8 mol L^?1 for accumulation time of 30 s. The validation of the procedure was performed by comparison of the results of analysis of river water samples with those obtained using other accepted voltammetric procedure.     

Elimination of SAS Interferences in Catalytic Adsorptive Stripping Voltammetric Determination of Cr(VI) by Means of Fumed Silica

In the work the procedure of chromium(VI) determination by catalytic adsorptive stripping voltammetry (CAdSV) with application of fumed silica, is presented. Two variants of the method are proposed: in the first fumed silica is put directly to the electrolytic cell containing tested solution, in the second the silica is shaken with the sample and next centrifuged. The effectiveness of many surface‐active substances removal from synthetic solutions as well as natural water samples, is studied. In the experiments the fumed silica (Sigma‐Aldrich) of the specific surface area in the range 200–390 m² g^?1 was used. Two types of the working electrodes were applied, i.e., hanging mercury drop electrode (HMDE) and cyclic renewable mercury film electrode (Hg(Ag)FE). In the silica presence i) the relative standard deviation (RSD) for 0.1 μg L^?1 Cr(VI) is <2% (HMDE) and <5% (Hg(Ag)FE), n=7, ii) the detection limits estimated deposition time 20 s were respectively 14 ng L^?1 (HMDE) and 22 ng L^?1 (Hg(Ag)FE). The accuracy of the method was tested by studying the recovery of Cr(VI) from spiked natural water samples.     

Sensitive Determination of Folic Acid using a Solid Bismuth Microelectrode by Adsorptive Stripping Voltammetry

An adsorptive stripping voltammetric procedure of folic acid determination with the use of a new voltammetric sensor with a prolonged application‐solid bismuth microelectrode was described. The proposed microelectrode is characterized by more eco‐friendly properties as compared to in situ formed bismuth film electrodes due to the fact that bismuth ions are not needed as a component of supporting electrolyte for metal film plating. Furthermore the above mentioned fact simplifies and shortens a measurements procedure. Parameters affected folic acid determination were studied. After a procedure optimization the calibration graph was found to be linear in the range: 5×10^?10 to 1×10^?8 mol L^?1 (accumulation time: 120 s). The obtained detection limit of folic acid determination for accumulation time of 120 s was 1.8×10^?10 mol L^?1. Possible interferences deriving from a presence of other organic and surface active compounds were studied. The analysis of pharmaceutical preparation was positively performed following the presented procedure.     

Catalytic Adsorptive Stripping Voltammetric Procedure for Determination of Total Chromium in Environmental Materials

A sensitive catalytic adsorptive stripping voltammetric procedure for determination of traces of total chromium in environmental samples is reported. The method is based on the preconcentration of a Cr(III)? H₂DTPA complex by adsorption at the HMDE from an acetate buffer solution at the potential ?1.0 V vs. Ag/AgCl. Total chromium was determined as Cr(III) after reduction of Cr(VI) to Cr(III) by NaHSO₃. In order to stabilize the signal of Cr(III) the measurements were performed at 5 °C. The calibration graph for chromium for an accumulation time of 60 s was linear in the range from 5×10^?10 to 5×10^?8 mol L^?1. The relative standard deviation for a chromium concentration of 1×10^?8 mol L^?1 was 3.9% (n=5). The detection limit for accumulation time of 60 s was about 8×10^?11 mol L^?1. The validation of the procedure was performed by the analysis of the certified reference materials.     

Determination of Platinum with Thiosemicarbazide by Catalytic Adsorptive Stripping Voltammetry (AdSV)

This work describes a very sensitive and selective voltammetric procedure for the determination of platinum. Instead of commonly used hydrazine, thiosemicarbazide as a component of supporting electrolyte was applied. The method is based on adsorption of platinum‐thiosemicarbazone complex, formed in situ in voltammetric cell from thiosemicarbazide and formaldehyde, coupled with a hydrogen catalytic reaction at a hanging mercury drop electrode. The linear relation between platinum concentration and height of analytical signal was observed up to 1.5×10^?9 mol L^?1 with the detection limit calculated as 1.5×10^?13 mol L^?1 (3 s of the blank) after 50 s of accumulation time. The effect of various interferences from other ions was studied. Described method was applied for platinum determination in hydroponically cultivated plants after microwave decomposition.     

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.     

Double Deposition and Stripping Steps for Trace Determination of Au(III) Using Anodic Stripping Voltammetry

A new way of decreasing the detection limit ‐ double deposition and stripping steps was proposed to determine trace amounts of gold(III) by anodic stripping voltammetry. Two carbon composite electrodes that differed drastically in their surface areas were used for the measurements. The calibration graph was linear from 1×10^?9 to 1×10^?8 mol L^?1 following deposition time of 300 s at the first and the second electrode. The detection limit was found to be 2.3×10^?10 and 1.4×10^?11 mol L^?1 for deposition time 600 and 2400 s, respectively. It is the lowest detection limit obtained so far for gold(III) determination in stripping voltammetry.     

Determination of Cadmium by Differential Pulse Adsorptive Stripping Voltammetry in the Present of Captopril

A new method is presented for determination of cadmium based on cathodic adsorptive stripping of the complex of cadmium with captopril,1‐[(2S)‐3‐mercapto‐2‐methylpropionyl]‐L ‐praline (CPL) at a hanging mercury drop electrode(HMDE). The most suitable operating conditions and parameters, such as pH, deposition potential, deposition time, ligand concentration, and others were selected and the determination of cadmium from aqueous solutions using the standard additions method was possible. Under the optimum conditions and for an accumulation time of 60 s, the measured peak current is proportional to the concentration of cadmium over the range of 1–300 nM. The limit of detection at S/N ratio of 3 was 0.3 nM and a relative standard deviation of 2.5% at 0.1 μM was achieved. The interference of other cations and anions was studied. The method was designed in order to determination of Cd in four analytical grade salts, with satisfactory results.     

Electroanalytical Detection of Cr(VI) and Cr(III) Ions Using a Novel Microbial Sensor

A microbial sensor, namely carbon paste electrode (CPE) modified with Citrobacter freundii (Cf–CPE) has been developed for the detection of hexavalent (Cr(VI)) and trivalent (Cr(III)) chromium present in aqueous samples using voltammetry, an electroanalytical technique. The biosensor developed, demonstrated about a twofold higher performance as compared to the bare CPE for the chosen ions. Using cyclic voltammetry and by employing the fabricated Cf–CPE, the lowest limit of detection (LLOD) of 1x10⁻⁴ M and 5x10⁻⁴ M for Cr(VI) and Cr(III) ions respectively could be achieved. By adopting the Differential Pulse Cathodic Stripping Voltammetric technique, the LLOD could be further improved to 1x10⁻⁹ M and 1x10⁻⁷ M for Cr(VI) and Cr(III) ions respectively using the biomodified electrodes. The reactions occurring at the electrode surface‐chromium solution interface and the mechanisms of biosorption of chromium species onto the biosensor are discussed. The stability and utility of the developed biosensor for the analysis of Cr(VI) and Cr(III) ions in chromite mine water samples has been evaluated.     

吸附溶出催化伏安法测定痕量锗

利用吸附溶出伏安法、极谱催化法测定痕量锗已有报道。但将吸附溶出伏安法与极谱催化法结合进行测定,尚未见报道。我们选择适当的体系和配位体3,4-二羟基苯甲醛(DHB)及氧化剂钒(V),首先使Ge(Ⅳ)-DHB络合物在悬汞电极上于一定电位处吸附富集一定时间,然后电位向负的方向扫描。当达到Ge(Ⅳ)-DHB络合物的还原电位时,Ge(Ⅳ)还原     

New Protocol for Determination of Rifampicine by Adsorptive Stripping Voltammetry

For determinations of organic compounds by adsorptive stripping voltammetry till now the same material of the electrode has been used for the accumulation and stripping steps. This paper describes a new protocol for extending the range of organic compounds, which can be determined by adsorptive stripping voltammetry. In the proposed procedure the accumulation step was performed on the electrode modified by a lead film, which assures adsorption of the studied species on the modified electrode and then the stripping step of the accumulated substance was performed on the support of the lead film electrode. As an example rifampicine was accumulated by adsorption at the lead film electrode while in the stripping step lead film and then the accumulated rifampicine were oxidized at a glassy carbon electrode. Using an acetate buffer as a supporting electrolyte a calibration graph for rifampicine in the range from 2.5×10^?10 to 1×10^?8 mol L^?1 was obtained. The detection limit for rifampicine following 60 s accumulation time was equal to 9×10^?11 mol L^?1. The obtained detection limit was comparable or lower than reported previously for other stripping voltammetric procedures. The proposed procedure was applied to rifampicine determination in pharmaceutical preparation.     

吸附溶出催化伏安法测定人参中的锗

本文提出了利用吸附溶出催化伏安法测定人参中锗的方法。最佳体系为:2.5×10~(-2)mol/LH_2O_2、2.0×10~(-2)mol/L邻苯二酚、2.0×10~(-3)mol/L H_2SO_4。线性范围为2.0×10~(-9)～2.0×10~(-7)mol/L。当富集时间为4 min时,最低检测浓度为4.0×10~(-10)mol/L。此法己成功地应用于测定人参中的锗。     

The Cyclic Renewable Mercury Film Silver Based Electrode for Determination of Uranium(VI) Traces Using Adsorptive Stripping Voltammetry

The new cyclic renewable mercury film silver based electrode (Hg(Ag)FE), applied for the determination of uranium(VI) traces using differential pulse adsorptive cathodic stripping voltammetry (DP AdCSV) is presented. The Hg(Ag)FE electrode with a surface area adjustable from 1.1 to 12 mm² is characterized by very good surface reproducibility (≤2%) and long‐term stability (more than 2 thousand measurement cycles). The mechanical refreshing of mercury film is realized in the simple constructed device, in a time shorter than 1–2 seconds. The effects of various factors such as: preconcentration potential and time, pulse height, step potential and supporting electrolyte composition are optimized. The calibration graph is linear from 0.4 nM (95 ng L^?1) to 250 nM (60 μg L^?1) for an accumulation time of t_acc=20 s, with correlation coefficient of 0.9996. For a Hg(Ag)FE with a surface area of 2.7 mm² the detection limit for an accumulation time of 120 s is as low as 12 ng L^?1. The repeatability of the method at a concentration level of the analyte as low as 2.4 μg L^?1, expressed as RSD is 2.5% (n=7). The proposed method was successfully applied and validated by studying the recovery of U(VI) from spiked river water and sediment samples.     

Determination of Folic Acid by Adsorptive Stripping Voltammetry at a Lead Film Electrode

An adsorptive stripping voltammetric procedure for the determination of folic acid at an in situ plated lead film electrode was described. Formation of lead film on a glassy carbon substrate and accumulation of folic acid was performed simultaneously from an acetate buffer solution of pH 5.6 at the potential ?0.88 V. The measurements were carried out from aerated solutions. The calibration graph for an accumulation time of 300 s was linear from 2×10^?9 to 5×10^?8 mol L^?1. The detection limit was 7×10^?10 mol L^?1, the relative standard deviation for 2×10^?8 mol L^?1 of folic acid was 3.9%. The proposed procedure was applied to folic acid determinations in pharmaceutical preparations.     

Determination of Cr(VI) in the Presence of Complexing Agents and Humic Substances by Catalytic Stripping Voltammetry

The voltammetric method of Cr(VI) determination in a flow system is proposed. Determinations can be carried out in the simultaneous presence of an excess of Cr(III), complexing agents, humic substances and surfactants. The method is based on the combination of a selective accumulation of the product of Cr(VI) reduction to the metallic state and a very sensitive voltammetric method of chromium determination in the presence of DTPA and nitrates. The calibration graph is linear from 1×10^?9 to 5×10^?8 mol L^?1 for accumulation time of 30 s. The relative standard deviation is 5.2% (n=5) for Cr(VI) concentration 1×10^?8 mol L^?1. The influence of humic and fulvic acids, complexing agents and surfactants on Cr(VI) and the interfering Cr(III) signal is presented. The method was applied to Cr(VI) determination in certified reference material, soil sample, natural water sample and EDTA extracts from soil certified reference material.     

Sensitive Simultaneous Determination of Rutin and Folic Acid with the Use of a Solid Lead Electrode by Means of Adsorptive Stripping Voltammetry

In this article a solid lead electrode (PbE) was utilized for the first time for determination of organic substances by means of adsorptive stripping voltammetry. A new procedure of simultaneous determination of rutin and folic acid was developed. Two well shaped and well separated reduction signals of rutin and folic acid were obtained with the use of PbE. The optimization of analytical procedure was presented. The calibration graphs for rutin and folic acid for an accumulation time of 120 s were linear in the ranges from 2×10^?9 to 1×10^?7 mol L^?1 and from 2×10^?9 to 5×10^?8 mol L^?1, respectively. The obtained detection limits for rutin and folic acid determination following accumulation time of 120 s were 7.9×10^?10 and 8.4×10^?10 mol L^?1. Potential interference effects were investigated. The proposed procedure was used for analysis of pharmaceutical preparations with satisfactory results showing practical applications. The analytical parameters of the proposed procedure were compared with other voltammetric procedures of mentioned substances determination.     

Determination of Cr(VI) in the presence of Cr(III) and humic acid by cathodic stripping voltammetry

A voltammetric procedure in the flow system for determination of traces of Cr(VI) in the presence of Cr(III) and humic acid is presented. The calibration graph is linear from 5×10⁻¹⁰ to 1×10⁻⁷ mol l⁻¹ for an accumulation time of 120 s. The R.S.D. for 1×10⁻⁸ mol l⁻¹ Cr(VI) is 5.3% (n=5). The detection limit estimated from 3σ for a low concentration of Cr(VI) and accumulation time of 120 s is 2×10⁻¹⁰ mol l⁻¹. The method can be used for Cr(VI) determination in the presence of up to 50 mg l⁻¹ of humic acid. The validation of the method was carried out by studying the recovery of Cr(VI) from spiked river water and by the comparison of the results of determination of Cr(VI) in a soil sample. The method cannot be used for analysis of samples containing high concentrations of chloride ions such as seawater and estuarine water.     

Catalytic Adsorptive Stripping Chronopotentiometric Determination of Hexavalent Chromium at a Silver Amalgam Film Electrode of Prolonged Application

The paper reports on the application of stripping chronopotentiometry for the determination of chromium(VI) at a silver‐based amalgam film electrode. It is the first attempt to apply such a detection system for the speciation of chromium. The procedure utilized catalytic reduction of nitrate ions induced by the instantaneous chromium(III)‐DTPA complex, accumulated at the electrode surface. The chronopotentiometric step is realized in the constant current mode. Several key parameters, such as the deposition potential, deposition time, nitrate concentration and stripping current were optimized. The detection limit obtained for 15 s of accumulation time was estimated at 0.025 µg/L. The repeatability of the signal was 6.1 %.     

Indirect Determination of Trace Copper(II) by Adsorptive Stripping Voltammetry with Zincon at a Carbon Paste Electrode

Traces of copper(II) can be determined by adsorptive stripping voltammetry using 2‐carboxy‐2′‐hydroxy‐5′‐sulfoformazyl benzene (Zincon) as complex forming reagent. First in phosphate buffer pH 6.4, copper(II)‐Zincon complex was adsorbed on carbon paste electrode (CPE) with an accumulation potential of 0.6 V. Following this, adsorbed complex was oxidized and detected by differential pulse voltammetric (DPV) scan from 0.6 to 1.0 V. The effective parameters in sensor response were examined. The detection limit (DL) of copper(II) was 1.1 μg/L and relative standard deviations (RSDs) for 10 and 200 μg/L Cu(II) were 1.81 and 1.03%, respectively. The calibration curve was linear for 2–220 μg/L copper(II). The resulting CPE does not use mercury and therefore, has a positive environmental benefit. The method, which is reasonably sensitive and selective, has been successfully applied to the determination of trace amount of copper in water and human hair samples.     

Amperometric Determination of Cr(III) and Cr(VI) by Flow Injection Analysis

Speciation of Cr(III) and Cr(VI) can be attained by flow injection analysis with amperometric detection. Cr(VI) is reduced in an acidic medium to Cr(III) with a glassy carbon electrode at —0.1 V vs. Ag/AgCl and the current is recorded. Cr(III) is oxidised on-line to Cr(VI) with alkaline hydrogen peroxide solution. From the difference of the total chromium and Cr(VI), the amount of Cr(III) was obtained. A linear calibration curve for Cr(VI) was obtained for the concentration ranges 0.01-5.0ppm of Cr(VI) and we have calculated the limit of determination to be about 0.5ppb. We have studied the degree of reproducibility obtained using the solid electrodes under various conditions. The influence of flow rate, coil length, interfenences and the extent of reaction were studied.