Voltammetric Peak Area as Instrumental Datum. A Possibility to Improve the Determination at Ultratrace Level Concentration of Platinum Group Metals (PGMs) and Lead. Application to Particulate Matter

Peak area as instrumental datum for determining the concentration of metals in solution instead of peak height is proposed for analytical voltammetric determinations. In the case of species present at ultratrace concentration level or having low reversibility degree of the electrodic processes, the employment of peak area permits to achieve limits of detection lower even more of one order of magnitude. The present work shows the possibility of determining at ultratrace level concentration Pd(II), Pt(II), Rh(III) and Pb(II) by voltammetry in particulate matter; these species, linked to vehicle emissions, show to have, in the supporting electrolytes employed, a very high irreversibility degree of the electrodic processes.     

Selenomethionine‐Catalyzed Nickel Ion Reduction at a Mercury Electrode: Applications in the Analysis of Nutritional Supplements

Selenomethionine (SeMet) is a catalyst for Ni²⁺ reduction at a mercury electrode in a borax buffer at pH around 9 and gives rise to a differential pulse voltammetric peak, A, at ?0.74 V vs. the Ag|AgCl, (3 M KCl) reference electrode. Peak current is directly proportional to SeMet concentration over the concentration range 0.4–10 μM. Alkali and alkali‐earth ions depress to some extent the sensitivity but the current‐concentration relationships remains linear even under these conditions. Differential pulse cathodic stripping voltammetry (DPCSV) in 0.01 M borax results in two partially overlapped peaks. The more negative (A, at about ?0.74 V) is similar to that recorded with no deposition and is due to the catalysis by nonadsorbed SeMet, whereas the more positive one (B, at about ?0.60 V) results from the catalysis by adsorbed SeMet. Only the DPCSV peak A appears if 0.1 M KNO₃ is also present along with 0.01 M borax. Stearic acid, which is present in nutritional supplement tablets, improves the separation of the DPCSV peaks. Consequently, the peak B recorded with 0.01 M borax buffer allows determining SeMet in nutritional supplement tablets by the standard addition method and enables discriminating between the organic and inorganic selenium forms.     

酵母核糖核酸在碳纳米管修饰电极上的电化学行为及其分析测定

研究了酵母核糖核酸（yRNA）在碳纳米管（MWNT）修饰电极上的电化学行为，优化了测定参数，在此基础上建立了一种直接测定yRNA的电分析测试方法。yRNA在碳纳米管修饰电极上于磷酸盐缓冲溶液中在0．758V处产生不可逆的氧化电流峰，峰电流与yRNA的质量浓度在1～10mg／mL之间有良好的线性关系，线性回归方程为：Iρ=0．0813ρ＋0．1807，相关系数r为0．9980，检出限为0．6mg／mL。     

Employment of peak area as instrumental datum for improving the voltammetric quantitative analysis of heavy metals in fresh and sea water in the presence of surfactants

Peak area instead of peak height is used for the simultaneous determination of Cu(II), Pb(II), Cd(II), and Zn(II) in fresh and sea water in the presence of anionic and cationic surfactants by differential pulse anodic stripping voltammetry. These species, if present, tend to make more irreversible the electrodic process of the metals. Because the employment of peak area for species having irreversible electrodic processes permits limits of detection about one or 2 orders of magnitude lower, this work shows the possibility of determining heavy metals at ultratrace level concentrations in the presence of surfactants, compounds which are always present in natural waters. The precision and accuracy of the analytical method were checked by the analysis of the standard reference materials (SRM) Fresh Water NIST-SRM 1643d, Sea Water BCR-CRM 403, and Estuarine Water BCR-CRM 505. The former, expressed as relative standard deviation (s(r)), and the latter, expressed as relative error (e), were satisfactory, being in all cases lower than 5%. The analytical procedure has been applied to fresh and sea water sampled in the Po river mouth area (Italy).     

Ultratrace Osmium,Ruthenium and Lead in Airborne Particulate Matter: Peak Area as Instrumental Datum to Improve Their Simultaneous Voltammetric Determination

Peak area as instrumental datum for determining the concentration of metals in solution instead of peak height is proposed for the simultaneous voltammetric determination in particulate matter of ultratrace Os(VIII), Ru(III) and Pb(II), species linked to vehicle emissions. In the case of species present at ultratrace concentration level or having low reversibility degree of the electrodic processes, the employment of peak area, instead of peak current, permits to achieve limits of detection lower even more of one order of magnitude. The method is based on the catalytic current of the Os(VIII)‐, Ru(III)‐ and Pb(II)‐bromate system by differential pulse voltammetry. 0.3 mol L^?1 acetate buffer pH 4.5+6.9×10^?2 mol L^?1 NaBrO₃+2.3×10^?4 mol L^?1 EDTA‐Na₂ was employed as the supporting electrolyte. For all the elements, the accuracy, expressed as relative error e%, and the precision, expressed as relative standard deviation s_r%, were satisfactory being lower than 6 %. To better validate the analytical procedure, a comparison with spectroscopic (electrothermal atomic absorption spectroscopy, ET‐AAS) is also reported.     

Differential Pulse Stripping Voltammetry of Mercury(II) Ions at a Cylindrical Carbon-Fiber Microelectrode in the Presence of Au(III) Ions

The determination of Hg(II) ions in aqueous solutions containing Au(III) ions was studied using differential pulse stripping voltammetry at a cylindrical carbon-fiber (d= 30 m) microelectrode fabricated from a pitch at 2800°C. At the [Au(III)]/[Hg(II)] ratio higher than 25, the anodic voltammogram of mercury accumulated in the potential range from 0.2 to –0.2 V for 40–200 s exhibited a current peak at 0.62–0.72 V. The peak height and area were directly proportional to the concentration of Hg(II) in the range (1–1000) × 10^–10M. The results of determining Hg(II) in waters of different origin are reported.     

血红蛋白在磷脂-月桂酸修饰的玻碳电极上的电化学行为及其分析应用

报道了血红蛋白（Hb）在磷脂-月桂酸修饰的玻碳电极上的电化学行为,在+0. 8～-0.7V (vs. Ag/AgCl)电位范围内,于pH6.0的0.01mol/L的KH_2PO_4- Na_2HPO_4底液中,血红蛋白产生不可逆的还原电流峰。还原峰电流与血红蛋白浓 度在1.25 * 10~(-8)～4.31 * 10~(-7) mol/L范围内呈良好线性关系。该电极可作 为检测血红蛋白的新型的高灵敏度电化学生物传感器。     

Capillary zone electrophoresis for the determination of average hydrodynamic velocity and diffusion coefficient

The determination of the average hydrodynamic velocity and diffusion coefficient by capillary zone electrophoresis is described. The present simple method only requires basic experimental data, such as peak area, peak height and migration time to complete the task of determining the diffusion coefficient and the average hydrodynamic velocity.     

Capillary zone electrophoresis hyphenated with laser-induced fluorescence detection for sensitive determination of noradrenaline and dopamine with 5-(4, 6-dichloro-s-triazin-2-ylamino) fluorescein as fluorescent label

A new capillary zone electrophoresis method with laser-induced fluorescence detection is presented for the determination of noradrenaline (NA) and dopamine (DA). The fluorescent reagent, 5-(4,6-dichloro-s-triazin-2-ylamino) fluorescein, which readily reacts with amine group under mild conditions, was initially used to label the two compounds. Under optimized separation and labeling conditions, linear relationship between peak area and analyte concentration was obtained with high sensitivity (nM level). The applicability of the method for complex sample analysis was validated by determining the two compounds in a human serum and an herb, Portulaca oleracea L with recoveries ranging from 89% to 102%.     

Validation of a capillary isoelectric focusing method for the recombinant monoclonal antibody C2B8

A capillary isoelectric focusing (cIEF) method has been developed for the purpose of determining the identity and charge distribution of mouse/human chimeric antibody to human CD20 antigen (C2B8). The assay was validated in accordance with ICH guidelines in order to demonstrate that it is suitable for its intended purpose and so that it may be performed as a lot release test for bulk and final product. As a result of the validation process the assay was found to be linear over the concentration range of 2–356 μg ml⁻¹ with recovery of ¹²⁵I-labeled C2B8 at the target sample concentration of 125 μg ml⁻¹ equal to 99%. The repeatability and intermediate precision relative standard deviations of the four major peaks for migration time, peak area, and peak area percent ranged from 0.9–4.4%. The specificity of the assay was demonstrated by baseline resolution of the C2B8 main peak from product excipients, and other Genentech monoclonal antibodies. The results of this validation demonstrate that the cIEF assay for the determination of identity and charge distribution of C2B8 is accurate, precise, linear, and highly specific. The assay is rapid and suitably rugged.     

Interaction of heparin and tetraarginine in capillary electrophoresis: Implication for analytical applications

Interactions between heparin and tetraarginine in an acidic background electrolyte were investigated in capillary electrophoresis. The results showed that tetraarginine and heparin form a stable complex that migrates toward the anode immediately after coming into contact. When a zone of tetraarginine at a mg/mL concentration level passes through a zone of heparin at a μg/mL concentration level, tetraarginine is gradually removed by the formation of the complex that migrates in the opposite direction, thereby decreasing the tetraarginine peak area. The variation of the tetraarginine peak area as a function of the unfractionated heparin concentration was linear within the range 2–20 μg/mL, which enables us to detect and determine heparin concentrations undetectable with a UV detector. The same behavior was confirmed for low molecular weight heparin.     

Anodic Oxidation Behaviors of Formaldehyde at Boron‐Doped Diamond Electrodes

The electrochemical behaviors of formaldehyde (FA) at boron‐doped diamond (BDD) electrodes are investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and linear scanning voltammetry (LSV) techniques. The CV results show that the oxidation reaction of FA is influenced by the hydroxyl concentration in the solution, and the peak current response with the FA concentration is linear at the range from 10 to 100 mM. The differential capacitance from EIS results indicate that the FA molecules adsorb at the BDD electrode surface at low potential (from 1.0 to 1.4 V). The kinetic studies have been examined with the various concentrations of FA, pH, and temperature. The activation energy of FA oxidation is also calculated. The results of kinetic study indicate that the adsorption of FA molecules at the BDD electrode is the rate‐determining step at low potential (from 1.0 to 1.40 V).     

Capillary zone electrophoresis for the determination of average hydrodynamic velocity and diffusion coefficient

The determination of the average hydrodynamic velocity and diffusion coefficient by capillary zone electrophoresis is described. The present simple method only requires basic experimental data, such as peak area, peak height and migration time to complete the task of determining the diffusion coefficient and the average hydrodynamic velocity. Received: 29 September 1998 / Revised: 14 May 1999 / Accepted: 19 May 1999     

Homocysteine Voltammetry at a Mercury Electrode in the Presence of Nickel Ions

At a mercury electrode, Hcy and Cys yield similar cathodic stripping peaks connected to the reduction of the pertinent mercury thiolate. However, due the different behavior as a ligand for nickel ion, the above compounds perform very differently in the presence of this ion. Whereas the nickel ion at a high enough concentration suppresses the Cys peak, in the case of Hcy it causes the cathodic peak to shift to more negative potentials. The peculiar behavior of Hcy is due to the stabilization of the mercury thiolate surface layer by intermolecular Ni²⁺ bridges within the surface layer. Conversely, in the case of Cys, the nickel ion strongly competes with the mercury ion and leads to the formation of a surface adsorbed bis‐cysteinatonickelate complex, which prevents the formation of mercury cysteinate. Such a difference allows determining Hcy by cathodic stripping voltammetry in the presence of nickel ion with no Cys interference.     

芬布芬电化学行为的线性扫描极谱法研究

应用线性扫描极谱法研究芬布芬的电化学行为.在0.2mol.L-1Na2HPO4-KH2PO4缓冲溶液(pH6.86)中,芬布芬于-1.38V(vs.SCE)处产生一灵敏的吸附波,其一次微分线性扫描峰电流与芬布芬浓度呈良好的线性关系,浓度范围1.6～200.0mg.L-1,相关系数r=0.9958(n=10),检出限为0.8mg.L-1.以80.0mg.L-1芬布芬溶液作6次平行试验,RSD为0.73%,回收率在97.7%～109.2%之间.芬布芬的此一电化学特性可用于其片剂含量测定.     

Comparison of the voltammetric studies at mercury and glassy carbon electrodes for the interaction of lumichrome with DNA and analytical applications

The determination of the interaction between lumichrome (LC), one of the products of decomposition of the biologically important flavins, and calf thymus double-stranded DNA was performed by using cyclic voltammetry (CV) and differential pulse stripping voltammetry (DPSV) in connection with a hanging mercury drop electrode (HMDE) or glassy carbon electrode (GCE). The nature of the process taking place at both electrode surfaces was clarified. It was found that the addition of DNA to a buffered LC solution results in the decrease of redox peak currents with changes in the peak potentials at both electrodes. We assume that LC interacting with DNA produces an electrochemically inactive supramolecular complex via intercalation. There was a difference between the electrochemical parameters determined at the HMDE and those at the GCE. The binding constants ( K) of the LC-DNA complex at HMDE and GCE were determined through the changes of peak currents and their values at the 10(5) level and 10(4) level with each nucleotide residue of DNA binding one LC molecule, respectively. Furthermore, the calibration graph for the determination of DNA was obtained by the decrease in the DPSV peak current of LC in the presence of DNA. Different variables, such as the concentration of LC, the accumulation time and solution conditions, were studied and optimised to maximize the sensitivity; in addition, the detection limit and the reproducibility were determined.     

Differential pulse cathodic stripping voltammetry of the copper complexes of glycyl-L-histidyl-glycine at a hanging mercury drop electrode

The behaviour of the copper complexes of glycyl-L-histidyl-glycine (GHG) was investigated using cyclic voltammetry and differential pulse voltammetry after their adsorptive accumulation on the surface of a hanging mercury drop electrode (HMDE). The nature of the observed cathodic and anodic peaks was established and optimum conditions were found for the differential pulse cathodic stripping voltammetric detemination of GHG at the 1 x 10(-8)M concentration level using adsorptive accumulation at -0.20 V vs. Ag/AgCl reference electrode and the cathodic stripping peak around -0.4 V (pH 8.3). This peak corresponds to the reduction of the Cu(I)-GHG complex formed at the HMDE surface as an intermediate in the reduction of Cu(II)-GHG to Cu(O)amalgam.     

血红蛋白在月桂酸修饰玻碳电极的电催化行为

研究血红蛋白在月桂酸修饰电极上的电化学行为,在0.02mol.L-1KH2PO4-Na2HPO4(pH=7)的缓冲液中,+0.6～-0.7V(vs.Ag/AgCl)电位范围内,Hb于该修饰电极产生不可逆还原电流峰.还原峰电流ip与v1/2呈线性关系,ip随溶液pH值和血红蛋白浓度的增加而增大,其浓度在1.00×10-8～5.00×10-9mol.L-1和1.92×10-6～2.06×10-7mol.L-1范围内分段呈线性变化关系.实验数据经进一步分析拟合,得到更精确的信息.该电极可作为检测血红蛋白的新型电化学生物传感器.     

Interaction of iodine species with glycogen at high concentrations of iodine

Glycogen–iodine (GI) complex formation has been studied at different concentrations of iodine and glycogen. For each glycogen concentration (0.25, 0.125, 0.0625, 0.0313 g/L), the iodine concentration was varied from 0.0317 to 1.59 g/L and the absorbance readings were taken at 453 and 560 nm (GI wavelengths of maximum absorbance). The 453 nm absorbance curves for the GI solution (GI complex and unreacted iodine), and that of the pure iodine solution (without glycogen) level off at a high iodine concentration, and give a peak in the subtracted curve. The 560 nm curves consistently increase in absorbance, and no peak is noticed in the subtracted curve. The spectra of concentrated iodine solutions in water and alcohol suggest the formation of neutral iodine clusters. We suggest that these iodine clusters do not react with glycogen, and that the GI complex formation takes place by the addition of I₂ molecules. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 927–931, 1997     

A new approach to glucose sensing at gold electrodes

An oxidative peak in the cathodic scan is observed in the cyclic voltammetry of glucose at gold electrodes, its peak current density being proportional to glucose concentration in a wide potential range. The application of this phenomenon in blood glucose sensing has been hindered by the presence of inhibitors: the most problematic are chlorides due to their high concentration and difficult separation from glucose. In the present paper we propose a solution to this problem involving a three electrode, four step pulsed electrochemical detection technique.