A study of the chemiluminescence behavior of myoglobin with luminol and its analytical applications

A chemiluminescence signal at 425 nm was observed when ferric state myoglobin was mixed with luminol in alkaline medium. Because the signal was remarkably enhanced in the presence of Fe(CN)₆ ^4–, analytical applications were investigated in a flow-injection system. The increase in chemiluminescence was linearly dependent on myoglobin concentration in the range 0.1 to 100 nmol L^–1, and the limit of detection was 0.04 nmol L^–1 with relative standard deviation 3.2% (3). It was also found that binding of Mb with the ligands CN^–, SCN^–, and F^– significantly inhibited the chemiluminescence reaction. The linear dynamic ranges for the ligands were 1.0–300.0, 0.1–3.0, and 0.5–100.0 nmol L^–1, and the limits of detection (S/N=3) 0.4, 0.04, and 0.2 nmol L^–1, for F^–, CN^–, and SCN^–, respectively. The relative standard deviations were 5.32%, 6.13%, and 3.38% for 0.1 nmol L^–1 CN^–, 0.5 nmol L^–1 SCN^–, and 1.0 nmol L^–1 F^–, respectively. At a flow rate of 2.0 mL min^–1 the assay could be accomplished in 1 min, including sampling and washing. The method has been successfully applied to the determination of myoglobin in human urine and F^– in water samples. A possible mechanism of chemiluminescence production by myoglobin and luminol is presented.     

Investigation of Copper(II) Interference on the Anodic Stripping Voltammetry of Lead(II) and Cadmium(II) at Bismuth Film Electrode

The bismuth‐coated electrode is known to be prone to errors caused by copper(II). This study investigates copper(II) interference at bismuth film electrode for the detection of lead(II) and cadmium(II). It was conducted using glassy carbon electrode, while the bismuth film was plated in situ simultaneously with the target metal ions at ? 1200 mV. Copper(II) presented in solution significantly reduced the sensitivity of the electrode, for example there was an approximately 70 % and 90 % decrease in peak signals for lead(II) and cadmium(II), respectively, at a 10‐fold molar excess of copper(II). The decrease in sensitivity was ascribed to the competition between copper and bismuth or the metal ions for surface active sites. Scanning electron microscopy (SEM) and energy dispersive X‐ray (EDX) analysis suggested a large decrease in the amount of bismuth nanoparticles formed on the electrode surface in the presence of copper(II) occurred, validating the competition between copper and bismuth ions for surface active sites. Recovery of the stripping signal of lead(II) and cadmium(II) was obtained by adding ferrocyanide ion to the solution. Finally, the proposed method was successfully applied to determine lead(II) and cadmium(II) in water samples and the method was validated by ICP‐MS technique.     

Influence of the Solvent on the “Casting” Methodology for MWCNT‐Modified Glassy Carbon and Platinum Electrodes

The choice of electrode material and surface preparation method are usually dictated by the suitability of the electrode to observe an electrochemical parameter, such as heterogeneous electron transfer rate, surface coverage, or redox potential. Thus, the glassy carbon (GC) and platinum (Pt) electrodes were modified with multiwalled carbon nanotubes (MWCNT) by direct “casting” modification using nine different aliquots of solvents. After drying at room temperature, the modified electrode showed distinct redox peaks corresponding to ferrocyanide oxidation/reduction. Using chemometrics, the cyclic voltammograms with higher current intensity were obtained for those in which ethanol, water and acetone as dispersing agents were used for GCE and dimethylformamide, water and acetone for Pt electrode modification.     

Mechanisms of oxidation of K4Fe(CN)6 by hypochlorous acid and catalytic activation by azide, bromide, and iodide

Summary HOCl reacts with Fe(CN) ₆ ^4– to generate an intermediate, presumably FeCl(CN) ₆ ^3– , which exhibits a weak absorption around 282 nm and decays simultaneously with the formation of Fe(CN) ₆ ^3– . When decreasing the HOCl/Fe(CN) ₆ ^4– concentration ratio fromR>1 toR<1, a drastic change in the kinetics of the oxidation is observed. Depending onR, the intermediate obviously oxidizes either Fe(CN) ₆ ^4– or HOCl. AtR1, a further intermediate appears which also precedes the oxidation and absorbs strongly around 360 nm. The intermediates detected may represent reactive high oxidation states of iron (Fe(IV) and Fe(VI)). HOCl induced oxidation of Fe(CN) ₆ ^4– is activated catalytically by Br^–, I^–, and N ₃ ^– , obviously due to generation of stronger oxidants (HOBr, HOI, and ClN₃), but oxidation is efficiently inhibited by CN^– and NCS^–.

---

Mechanismen der Oxidation von K₄Fe(CN)₆ durch Hypochlorsäure und katalytische Aktivierung durch Azid, Bromid und Iodid

Zusammenfassung HOCl reagiert mit Fe(CN) ₆ ^4– unter Bildung eines Intermediats, vermutlich FeCl(CN) ₆ ^3– , das bei 282 nm eine schwache Absorption aufweist und parallel zum Erscheinen von Fe(CN) ₆ ^3– verschwindet. Man beobachtet eine drastische Änderung in der Oxidationskinetik, wenn das HOCl/Fe(CN) ₆ ^4– Konzentrationsverhältnis vonR>1 zuR<1 verändert wird. In Abhängigkeit vonR wird offenbar entweder Fe(CN) ₆ ^4– oder HOCl durch das Intermediat oxidiert. FürR1 erscheint ein weiteres Intermediat mit einer starken Absorptionsbande bei 360 nm, das ebenfalls der Oxidation vorangeht. Bei den beobachteten Intermediaten handelt es sich vermutlich um reaktive höhere Oxidationsstufen des Eisens (Fe(IV) und Fe(VI)). Die HOCl-induzierte Oxidation von Fe(CN) ₆ ^4– wird einerseits durch Br^–, I^– und N ₃ ^– katalytish aktiviert (offenbar infolge der Bildung stärkerer Oxidantien wie HOBr, HOI und ClN₃), andererseits durch CN^– und NCS^– effektiv inhibiert.

     

网状玻璃碳光谱电化学池的制作及应用

制作了一种以网状玻璃碳为工作电极的光谱电化学池,并介绍了对网状玻璃碳电极的处理方法。选用铁氰化钾-亚铁氰化钾体系,对其式量电位(E°′)、反应电子数(n)和扩散系数(D_R)进行了测定,取得较为满意的结果。     

Simulation of Redox‐Cycling Phenomena at Interdigitated Array (IDA) Electrodes: Amplification and Selectivity

We present Finite Element Method (FEM) simulations of interdigitated array (IDA) electrode geometries to study and verify redox selectivity and redox cycling amplification factor. The simulations provide an adequate explanation of an earlier found, but poorly understood, high amplification factor (65×) in a 1 μm‐spaced IDA microdevice. Moreover, using the FEM calculations we present selectivity measurements with IDA electrodes in a mixture of two redox species, as for example dopamine and ferricyanide. We show that it is possible to electrochemically detect dopamine in presence of the stronger reductor ferricyanide, which is impossible with direct amperometric detection, with the use of IDA electrodes with proper polarization potential of the collector electrode. Using our simulations, we show that a theoretical selectivity of dopamine over ferricyanide of 11 can be achieved.     

Microwave Activation of Electrochemical Processes in Ionic Liquid Impregnated Ionomer Spheres

The redox system K₄Fe(CN)₆ adsorbed into anion exchanger particles (Dowex 1×2 of typically 200 µm diameter) and impregnated with 1‐butyl‐3‐methyl‐imidazolium tetrafluoroborate ionic liquid (BMIM⁺BF₄^?) in contact to a 50 µm diameter platinum microelectrode show well‐defined Fe(III/II) voltammetric responses. Processes are studied at the ionic liquid sphere | electrode | gas interface in the presence of dry or 80 % relative humidity argon gas flow. Due to the hygroscopic nature of BMIN⁺BF₄^? currents are sensitive to humidity levels. Pulsed and continuous microwave activation (2.45 GHz) is shown to occur locally at the tip of the platinum microelectrode due to focusing of microwave energy. Impedance experiments reveal the presence of a thin active film of ionic liquid.     

Enhanced Electron Transfer Properties of Carbon Spheres Chains via Electrochemical Functionalization

Electrochemical functionalization via electrochemical oxidation in nitric acid of various concentrations (0.1 M, 0.2 M and 2 M) was employed to enrich the surface of carbon sphere chains (CSCs) with some useful physico‐chemical properties such as hydrophilicity, oxygen functionalities and electron transfer properties. The functionalization process in 2 M HNO₃ solution led to the creation of an original hybrid material made of carbon sphere chains‐carbon nanobuds. This material displayed a prominent response towards the electrocatalytic oxidation of ferrocyanide with a peak current three times and twice superior to those delivered by pristine CSC and multiwalled carbon nanotubes (MWCNTs) electrodes, respectively.     

How anthraquinones can enable aqueous organic redox flow batteries to meet the needs of industrialization

Owing to the importance of storage and its hybridization with renewable energy technologies for the energy transition, a high attention has been paid towards the development of redox flow batteries. Among all different emerging technologies, aqueous organic redox flow batteries (AORFBs) are particularly attractive since the objectives in terms of sustainability, cost and safety issues can be achieved owing to the high possibilities offered by molecular engineering, organometallic and coordination chemistry. Thus, AORFBs based on anthraquinones paired with ferrocyanide in basic medium have been widely developed and are close to reach the performances required for industrial processes. This review aims to focus on the main parameters making possible the integration of anthraquinone derivatives as negolyte in AORFB with a special attention for their implementation in industrial process.