Studies on the second reciprocal derivative constant-current stripping analysis

Theoretical and experimental investigation have been made on a method called the second reciprocal derivative constant-current stripping analysis (SRD-CCSA). The SRD-CCSA is based on the measurement of the d(2)t/dE(2) signal given by the curve of (d(2)t/dE(2)) versus the electrode potential (E). The d(2)t/dE(2)-E curve gives a maximum value (d(2)t/dE(2))(max) and a maximum value ((d(2)t/dE(2)))(min), which show as two peaks on the curve. Either of the heights of the peaks and the sum of absolute values of the two peaks are proportional to the bulk concentration of the analyte in solution, and they are much larger than (dt/dE)(p) in the first reciprocal derivative constant-current stripping analysis (FRD-CCSA). The ratio of peak-peak height in the SRD-CCSA to peak height in the FRD-CCSA is about 43n (where n represents the number of electrons transferred during the electrode process for the analyte). Potential difference (W(pp)) between the two peaks is 48.2 mV n(-1) at 25 degrees C in the SRD-CCSA, which is noticeably smaller than the half-height width W(p/2), 65.5 mv n(-1), in the FRD-CCSA. The theory was verified with a home-made multireciprocal derivative measuring instrument. The experimental results were in good agreement with the theoretical ones.     

Interaction of DNA with echinomycin at the mercury electrode surface as detected by impedance and chronopotentiometric measurements

The capacitance measurement (dependence of the differential capacitance C of the electrode double layer on potential E, C-E curves), electrochemical impedance spectroscopy (frequency response of the impedance Z of the electrode double layer-EIS) and constant current chronopotentiometry (dependence of dt/dE on potential at constant current, chronopotentiometric stripping analysis-CPSA) have been used for electrochemical study of echinomycin and its interaction with single-stranded (ss) and double-stranded (ds) DNA at the hanging mercury drop electrode (HMDE). The capacitance measurement showed that echinomycin gives a pseudocapacitance redox peak strongly dependent on the a.c. voltage frequency at the potential of -0.53 V. This peak is observed with dsDNA-echinomycin complex as well, but not with ssDNA treated by echinomycin. Similar results were obtained using CPSA measurements. Thus capacitance measurements and CPSA can distinguish with the aid of the bis-intercalator echinomycin the single-stranded and double helical form of DNA adsorbed at the mercury electrode surface. Impedance measurement in connection with adsorptive transfer technique can find the differences between ssDNA and dsDNA, which promise to use this technique for detection of dsDNA in hybridisation reactions.     

倒数示波计时电位法

使用dE/dt的倒数对E作图的示波计时电位法,称为倒数示波计时电位法.dE/dt-E曲线上的切口在dE/dt^-1-E上变成峰,可以方便地扣除充电电流,提高分析测试的灵敏度.     

Absolute analysis of trace metals through galvanostatic stripping chronopotentiometry with signal accumulation

An electrochemical flow-through cell with a porous working electrode made of vitreous carbon particles and plated with mercury was used for the absolute determination of Pb using galvanostatic stripping chronopotentiometry in a flow system. After completing the potentiostatic electrodeposition of the analyte from the flowing sample solution the flow was stopped and oxygen in the solution inside the pores of the electrode was removed by reducing it. The deposit was then stripped by applying a constant current of 50 to 1000 A and the measured potential vs time (E vs t) data were converted to the dt/dE vs E dependence by a memory mapping technique. Owing to the thin layer properties of the cell, the stripping/deposition steps could be repeated reproducibly enabling the accumulation of the signals while improving the signal to noise ratio. The method was also found to be suitable for the simultaneous determination of Cd, Pb and Cu. The experimental conditions, computerized data handling and signal processing have been investigated. Water, grass and sediment samples were analyzed for traces of Pb.     

铋膜电极微分电位溶出法测定生物材料中痕量铅

研究了镀铋膜电极替代镀汞膜电极痕量铅的微分电位溶出分析法(DPSA)。考察并优化了同位镀铋膜测定铅的条件。结果表明,在HAc-NaAc(pH=4.4)介质中,铅可在镀铋膜电极上得到灵敏的微分电位溶出峰;利用标准加入法对人尿及血中痕量铅进行了测定。本法避免了镀汞膜电极对人体健康及环境的危害。     

电化学预处理玻碳电极微分计时电位溶出法测定DNA中的嘌呤碱基及DNA浓度

研究了鸟嘌呤(G)、腺嘌呤(A)、鸟嘌呤核苷、腺嘌呤核苷和变性DNA在电化学预处理玻碳电极上的恒电流微分计时电位溶出行为. 实验结果表明, 用电化学方法预处理玻碳电极操作简单, 效果明显, 预处理玻碳电极对嘌呤及其核苷和DNA的吸附能力大大增强, 用微分计时电位溶出法可以得到灵敏的溶出峰, 溶出峰高(dt/dE)与其浓度在一定范围内呈良好的线性关系, 可用于嘌呤碱基及其核苷的定量检测和DNA浓度的测定. 将该方法应用于酸变性DNA样品中鸟嘌呤与腺嘌呤的同时测定, 选择性好、灵敏度高; 还可获得有关DNA损伤的一些信息.     

Catalytic signal of rabbit liver metallothionein on a mercury electrode: a combination of derivative chronopotentiometry with adsorptive transfer stripping

Constant current chronopotentiometric stripping analysis (CPSA) in combination with adsorptive transfer stripping (AdTS) technique was used to study the rabbit liver metallothionein (MT) on a hanging mercury drop electrode (HMDE). Metallothionein yielded a distinct, sharp chronopotentiometric signal at very negative potentials (about -1.7 V), also known as the "peak H". The height and potential of this peak were dependent on experimental conditions, such as buffer composition, pH, and the presence oxygen in solutions. The peak H was highest in borate buffer with pH close to the isoelectric point (pI) of MT. The chronopotentiometric results contribute to a deeper understanding of the nature of catalytic hydrogen evolution and demonstrate the usefulness of the peak H in peptide and protein research.     

硒碳糊电极微分电位溶出法测定铜和铋

建立了掺杂硒碳糊电极同时测定铜和铋的微分电位溶出法。在HCl(0.05mol/L)中,在-0.3V(vs.Ag/AgCl)下,Cu2+和Bi3+电沉积在电极表面,再在溶液中溶解氧的作用下,铜和铋从电极表面溶出,分别于0.30V和0.02V获得灵敏的电位溶出峰。微分电位溶出峰高(dt/dE)与铜和铋的浓度成线性关系,线性范围为5.0×10-9～1.55×10-7mol/L,检出限分别为4.0×10-9和2.5×10-9mol/L(S/N=3)。方法用于实际样品中铜和铋的测定,结果令人满意。     

平面汞膜电极二阶倒导数电位溶出分析法研究

对电位溶出的Ｅ－ｔ曲线进行二阶倒导数处理，提高了二阶倒导数电位溶出分析法理论，其信号较一阶倒导数法增强约４３．１ｎ倍，分辨率由原来的６５．５ｍＶ／ｎ改善到４８．２ｍＶ／ｎ。用根据二阶倒导数法原理自行设计研制的多阶倒导数电位出仪验证了本提出了的理论，富集１２０ｓ，Ｃｄ＾２＋的检测限可达１．０×１０＾－１０ｍｏｌ／Ｌ。     

Application of potentiometric stripping analysis for speciation of copper complexes with a non-adsorbable ligand on a mercury electrode

Potentiometric stripping analysis (PSA) was used for determination of conditional stability constants (delta') of copper(II) complexes. Glycine was used as a model of a non-adsorbable ligand on the mercury electrode that forms well defined 1:1 and 1:2 copper(II)-glycine complexes, which are labile within the time scale of the analytical technique. The calculations were performed by the DeFord-Hume method, which was applied to the shifts in peak potential (dt/dE vs. E) provoked by the presence of different concentration of the ligand in the metal solution. For comparison purposes, the study was also carried out by differential pulse anodic stripping voltammetry (DPASV). The results obtained by PSA both at pH 6.0, logbeta'(1) = 5.0 +/- 0.2 and logbeta'(2) = 7.6 + 0.2, and at pH 6.5, logbeta'(1) = 5.7 +/- 0.6 and logbeta'(2) = 8.5 +/- 0.4 (standard deviations are given), were in agreement with those obtained by DPASV and from the literature, which indicates that PSA is suitable for this type of study.     

Chronopotentiometric Determination of Redox States of Peptides

Reduced and oxidized forms of peptides were studied by different electrochemical methods at carbon and hanging mercury drop (HMDE) electrodes. Striking differences between the reduced and oxidized peptides were obtained by constant current chronopotentiometric stripping analysis (CPSA) at HMDE. Peptides yielded electrocatalytic peak H at highly negative potentials (ca. ?1.75 V). Reduced peptides adsorbed at positively charged HMDE produced substantially higher peak H than the oxidized forms. Voltammetry reflected the peptide redox state less efficiently. Different orientation of reduced and oxidized molecules at the positively charged electrode and very fast potential changes in CPSA were probably responsible for the observed effects.     

Investigations on Adsorption Potentiometry Part V Derivative Adsorption Chronopotentiometry of Beryllium(II)-4-[(4-diethylamino-2-hydroxypheanyl)-azo]-5-hydroxy-naphthalene-2,7-disurphonic Acid System

Abstract

An electroanalytical methood, based on derivative chronopotentiometry of the complex of beryllium(II) with 4-[(4-diethylamino-2-hydroxy-phenyl)-azo]-5-hydroxy-naphthalene-2,7-disurphonic acid (Beryllon II) accumulated adsorptively on the surface of a hanging mercury drop electrode, has been developed for determining trace beryllium in food. The dependences of the peak height on the dt/dE vs. E curve on the pre-concentration time, preconcentration potential and the constant reducing current are discussed. In 0.15 mol/1 NH_s+0.05 mol/1 NH₄Cl, 4×10^?7 mol/l Beryllon II, and at a preconcentration potential of -0.30 V (ve. SCE), the limit of detection and linear range are 1 × l0^?10 mol/l and 3 × 10^?10 -2 × l0^?7 mol/l, Iwpectively. The relative standard error of the method is 2.3% for 6 × 10^?8 mol/l Be(II). The method WBB applied to samples of food. The electrode procees hae been diecueeed.     

Catalytic stripping analysis: sensitivity enhancement for reciprocal derivative constant-current stripping determination of palladium in the presence of tin(II) during stripping

The reciprocal derivative constant-current stripping signal of palladium at a mercury film electrode is increased, as in anodic stripping voltammetry (ASV), by a factor of ca. 80 if a certain amount of tin(II) is present in the stripping solution. This catalytic stripping phenomenon has been successfully used as a means of sensitivity enhancement in constant-current stripping determination of trace palladium. The limit of detection is 4 x 10(-10)M at S/N = 3, which is about two decades lower than that obtained without tin(II) present. Linear response was observed over the range 10(-10)-10(-7)M. This method has been applied to determine palladium in waste water and mineral samples. The experimental results support the postulated mechanism of signal enhancement, namely a chemical redeposition reaction occurring during the stripping, giving a cycle of stripping and deposition and thus increasing the stripping signal.     

芦荟大黄素1.5阶微分阳极溶出伏安法测定及电化学性质研究

研究了芦荟大黄素在以 0 .1mol/LHAc (pH 2 .89)为支持电解质 ,玻碳电极为工作电极的吸附伏安行为 .结果表明芦荟大黄素存在一个准可逆的双电子转移过程 ,其峰电流Ip 和峰电位Ep 与溶液 pH值有关 .同时还建立了用 1.5阶微分阳极溶出伏安法测定含量的新方法 .在 - 0 .80V(vs.SCE)电位下富集 ,可得一灵敏的微分阳极溶出峰 ,峰电位Ep 为 - 0 .38V ,峰电流Ip 与芦荟大黄素的浓度在 2 .0× 10 - 7～ 8.0× 10 - 6 mol/L范围内成线性关系 ,最低检出限为 1.0× 10 - 7mol/L .该法用于含有芦荟大黄素体系的测定 ,具有简便、快速、准确等优点     

Electrochemistry of riboflavin-binding protein and its interaction with riboflavin

Riboflavin-binding protein (RBP, a carrier of riboflavin) plays an essential role in embryo development. Electrochemical studies of the riboflavin–RBP interactions have been so far limited to changes in polarographic and voltammetric responses of riboflavin because of lack of methods capable to detect electrochemical changes in the RBP responses. Here we used constant current chronopotentiometric stripping analysis (CPSA) with the hanging mercury drop electrode (HMDE) and square wave voltammetry (SWV) with carbon paste electrode (CPE) to investigate RBP. We found that CPSA of RBP produces electrocatalytic peak H, capable to discriminate between apoprotein and holoprotein forms of RBP. This peak is suitable for studies of RBP–riboflavin interaction at nanomolar concentrations. We observed no sign of a release of riboflavin from holoprotein adsorbed at the HMDE surface. SWV at CPE required higher concentrations of RBP and displayed almost identical oxidation peaks of apoprotein and holoprotein.     

恒电流吸附计时电位法的研究 Ⅱ.铜、铅的微分吸附计时电位法连测

研究了ＮＨ３／ＮＨ４Ｃｌ底液中，铜、铅与水杨基荧光酮（ＳＡＦ）形成的络合物在悬汞电极上的恒电流吸附计时电位溶出行为。讨论了富集时间，溶液ｐＨ值，溶出恒电流大小及铜、铅浓度比值等对ｄｔ／ｄＥ～Ｅ溶出曲线的影响。并得出了连测铜铅的条件。     

The Simultaneous Determination of Cu Pb Cd and Sb by Derivative Adsorption Chronopotentiometry

The behaviour of the complexes of copper,lead,cadmium and antimony with salicylfluorone(SAF)adsorbed on HMDE has been investigated by derivative chrono potentiometry in NH3/NH4C1.The dependence of the peak height on the dt/dE vs E curve on preconcentration time,the pH of solution and the constant reducing current are discussed.This method achieved the simultaneous determination of copper,lead,cadmium and antimony in human hair.     

The Simultaneous Determination of Cu Ph Cd and Sb by Derivative Adsorption Chronopotentiometry

Anodic stripping voltammetry (ASV) is an effective electroanalytical technique for themeasurement of trace metal ions. But there are serious interferences due to overlappingstripping peaks and forming of intermetallic complex in complicated system. The peak ofcopper (ASV) is close to that of mercury. So the result of determination of copper is notsatisfactory. Adsorption chronopotentiometry was reported by H.Eskilsson et al i. In thismethod, instead of electrolytic accumulation of metal io…     

3.5次微分循环示波计时电位法的研究

将半积分半微分技术应用于循环示波计时电位曲线的处理,可大大抑制充电电流的影响,提高示波测定的灵敏度和分辨率.据此,本文提出了3.5次微分循环示波计时电位法,研究了该方法的特点并将其用于HAc-NaoH-铜铁试剂(HCup)体系中铅示波特性的研究和微量铅的测定.     

改进示波计时电位法

本文克服了dE/dt～E曲线线性范围窄、分辨率差等缺点,把dE/dt～E曲线的切口变成峰形,具有再现性好、线性范围宽、灵敏度高、分辨率好等优点.采用内标法和频谱分析进行了定量测试工作,取得了满意的结果.