Compounds In Alkaline Media Research Articles

Decolourisation of Metal-azo Dyes in Wastewaters by Sodium Peroxodisulphate: A Template for Experimental Investigations

Background: It has long been recognized that the presence of azo metal complex dyes and their non-complexed counterparts in wastewaters, which is due to their manufacturing and use in the textile industries, renders natural waterways intensely coloured, and is therefore aesthetically unacceptable. Azo dye moieties are also known to be precursors of human carcinogenicity. Objective: This work aimed at the decolourisation of metal-azo dyes present in wastewaters so that pollution of natural bodies of water can be prevented. Decolourisation is indicative of the destruction of the metal-ligand complex, allowing the retrieval of transition metal ions, which are also water contaminants. Fracturing of the azo bond itself minimizes the potential for the carcinogenicity of these dyes. Methods: Decolourisation is achieved by the oxidative action of free radicals furnished by Na2S2O8, the sodium salt of peroxodisulphuric acid (Marshall’s acid). Raman spectroscopy characterizes the dye (ligand) known as “Eriochrome Black T (EBT)” by a peak at 1425 cm-1. Dismantling of its molecular structure by peroxodisulphate will lead to decolourisation accompanied by the collapse of the peak. Concomitantly, as EBT ligands fracture and cease to chelate, metallic ions are released, oxidized to a higher oxidation state, and precipitated as insoluble compounds in alkaline media. Results: The concentration of metallic ions in the aqueous phase has been found to be substantially reduced. The successfully treated dye solutions are mostly clear and colourless; their Beer-Lambert absorbances are in the range of 0.02 ≤ absorbance ≤ 0.05. The treatment of Ni(II), Co(II) and Fe(II)-EBT solutions is straightforward; the Cu(II) and Cr(III)-EBT solutions require additional treatment to be included in the above absorbance range. The Cr(III)-EBT is the least responsive to treatment. Fracturing of the azo bond is evinced by Raman Spectroscopy. Conclusion: A template to investigate the feasibility of decolourisation of metal-complex dye solutions is pioneered and recommended.

Decolourisation of Metal-Azo Dyes in Wastewaters by Sodium Peroxodisulphate: A Template for Experimental Investigations

Background It has long been recognized that the presence of azo metal complex dyes and their non-complexed counterparts in wastewaters, which arise from their manufacturing and their use in the textile industries, renders natural waterways intensely coloured, and is therefore aesthetically unacceptable. Azo dye moieties are also known to be precursors of human carcinogenicity. Objective This work aimed at the decolourisation of metal-azo dyes present in wastewaters so that pollution of natural bodies of water can be prevented. Decolourisation is indicative of the destruction of the metal-ligand complex, allowing the retrieval of transition metal ions, which are also water contaminants. Fracturing of the azo bond itself minimizes the potential for carcinogenicity of these dyes. Methods Decolourisation is achieved by the oxidative action of free radicals furnished by Na2S2O8, the sodium salt of peroxodisulphuric acid (Marshall’s acid). Raman spectroscopy characterizes the dye (ligand) known as “Eriochrome Black T (EBT)” by a peak at 1425 cm-1. Dismantling of its molecular structure by peroxodisulphate will lead to decolourisation accompanied by the collapse of the peak. Concomitantly, as EBT ligands fracture and cease to chelate, metallic ions are released, oxidized to a higher oxidation state, and precipitated as insoluble compounds in alkaline media. Results The concentration of metallic ions in the aqueous phase has been found to be substantially reduced. The successfully treated dye solutions are mostly clear and colourless; their Beer-Lambert absorbances are in the range of 0.02 ≤ absorbance ≤ 0.05. The treatment of Ni(II), Co(II) and Fe(II)-EBT solutions is straightforward; the Cu(II) and Cr(III)-EBT solutions require additional treatment to be included in the above absorbance range. The Cr(III)-EBT is the least responsive to treatment. Fracturing of the azo bond is evinced by Raman Spectroscopy. Conclusion A template to investigate the feasibility of decolourisation of metal-complex dye solutions is pioneered and recommended.

A Facile Synthetic Strategy for Decavanadate and Transition Metal Based All‐Inorganic Coordination Polymers and Insights into Their Electrocatalytic OER Activity

AbstractThis study reports a facile synthetic strategy for decavanadate ([V10O28]6−) cluster‐based all inorganic coordination polymers (CPs) containing earth‐abundant and redox‐active transition metals and their electrocatalytic oxygen evolution reaction (OER) activity. The first series of such isomorphous compounds containing the transition metals Mn, Co, and Ni, {(H2O)2K‐μ‐(H2O)3Mn(H2O)3}2n[V10O28]n (1), {(H2O)2K‐μ‐(H2O)3Co(H2O)3}2n[V10O28]n (2) and {(H2O)2K‐μ‐(H2O)3Ni(H2O)3}2n[V10O28]n (3), have been synthesized and structurally characterized. In these polymeric compounds, the [V10O28]6− clusters are interlaced and inter‐connected by {(H2O)2K‐μ‐(H2O)3‐M(H2O)3}+3 units leading to a linear chain‐like arrangement. Each of such chains is further interconnected to adjacent chains by bonding K+ ions with a [V10O28]6− cluster of the adjacent chain leading to a two‐dimensional (2D) sheet‐like arrangement. Hydrogen bonding interactions between the coordinated water molecules and the cluster oxygens further interconnect the adjacent sheets. All these compounds 1–3 are shown to catalyze the oxygen evolution reaction (OER) under alkaline (0.1 M KOH) conditions. Among the three, the Ni‐based catalyst 3 exhibited the best OER activity with a moderate overpotential of 270 mV at onset, a low Tafel slope of 89 mV dec−1, and a turnover frequency (TOF) of 7.5 s−1, which is comparable to similar Keggin POM‐based systems reported so far. The CPs were not highly stable under the OER conditions employed. The post‐catalytic analyses indicated the ‘precatalyst’ nature of these compounds in alkaline media forming V‐doped metal oxyhydroxides as the OER active species under the turnover conditions. Thus, this study provides a new and facile strategy for synthesizing [V10O28]6−cluster and transition metal‐based all‐inorganic CPs and insights into their OER electrocatalytic activities for the first time.

Understanding the behaviour of zinc and impurities during alkaline leaching of zinc bearing product obtained as a result of pyrometallurgical processing of ferrous metallurgy dusts and examining the phase composition of leaching residue

This paper describes a technique developed for processing EAF dusts and recovering zinc. The technique is based on the Waelz process without zinc sublimation and allows to obtain a product suitable for hydrometallurgical processing and clear of lead or halogens in one process stage. It would be feasible to use an alkaline hydrometallurgical process for this product as it enables a selective recovery of zinc while iron remains in the solid residue. A pyrometallurgical process is necessary to remove halogens, increase the solubility of zinc and remove lead. In the alkaline process, the latter transfers to the solution together with zinc. As part of the development procedure, the thermodynamics of lead and iron in alkaline medium was studied. For this, equilibrium diagrams were built in the Eh – рН coordinates. Findings: – zinc can dissolve at рН > 12.7 while forming the following anions: ZnO22– and [Zn(OH)n]2–n. A study that looked at leaching zinc ores confirms that anions of the latter type do form; – lead can dissolve while forming [Pb(ОН)6]2–-type hydroxo complexes at рН > 12.5. When the solution is heated to 80 oС, their solubility can reach 140 g/dm3. In a hot solution hydroxo complexes form orthoplumbite and orthoplumbate ions PbО22–, PbО32– as a result of dehydration; – the low solubility of all iron compounds in alkaline medium and their position in the diagram only defined by the pH range suggest that the leach solutions contain no iron ions of any type. With the temperature raised to 80 oС, the equilibria in the Fe – H2O system remains unchanged in alkaline medium and no significant increase in the solubility of iron compounds is observed. The findings show that selective dissolution of products containing zinc oxides (including EAF dusts after the above mentioned pyrometallurgical process) in alkaline solutions is feasible. The zinc leaching residue was analyzed for chemical and phase composition to find possible applications for it. It is demonstrated that calcium ferrites, aluminates and alumosilicates account for 80% of the residue. This iron-calcium material can be utilized by cement industry.

Oxygen Electrocatalysis on Mixed-Anion Perovskite Compounds in Alkaline Media

Enhancement of oxygen reduction and evolution reaction (ORR and OER) performance has been considered to play a key role for the development of next-generation energy storage devices such as metal-air batteries and water electrolyzers. Recently, mixed-anion compounds have been found to be highly efficient bifunctional electrocatalysts for ORR and OER[1,2]. Our group has been also clarified that layered perovskite oxychloride Sr2Co1 − x Fe x O3Cl serves as a good bifunctional catalyst, whose OER activity outperformed that of Ba0.5Sr0.5Co0.8Fe0.2O3 −δ [3]. While detailed mechanism of its enhanced OER activity has been discussed previously[4], that of ORR has not been evaluated in detail, even though ORR pathway is generally considered to be much more complicated. Moreover, further exploration of highly active bifunctional mixed-anion perovskites has to be continued for better understanding of oxygen electrocatalysis on mixed-anion perovskite compounds. In the present research, therefore, we focused on the evaluation of ORR pathway for Sr2Co1 − x Fe x O3Cl, and oxygen electrocatalysis on other mixed-anion perovskite compounds in alkaline media.Solid-state method was applied to the synthesis of Sr2Co1 − x Fe x O3Cl and other mixed-anion perovskites. Electrochemical measurements were conducted by a three-electrode cell with a rotating disk electrode (RDE). Glassy carbon RDEs coated by a catalyst layer consisting of catalysts, Vulcan XC-72 (Cabot), and AS-4 (Tokuyama) were used for the working electrode. Pt wire and reversible hydrogen electrode were used for the counter and reference electrodes, respectively. Oxygen-saturated 1 mol dm− 3 KOH solution was used for ORR activity tests, and Argon-saturated 1 mol dm− 3 KOH solution containing 5 mmol dm− 3 H2O2 was used for the activity tests of peroxide reduction reaction (PRR). Peroxide decomposition rates of Sr2Co1 − x Fe x O3Cl were performed by measuring evolved oxygen gas in the same manner as previously described[5].While the highest OER activity was observed at x = 0.2, ORR activity of Sr2Co1 − x Fe x O3Cl was monotonously decreased with increase of Fe doping. Figure 1 shows decomposition rates of Sr2Co1 − x Fe x O3Cl in 1 mol dm− 3 KOH. Surprisingly, their HO2 − decomposition rate was higher than those of cobalt-based perovskite oxides such as LaCoO3, whose ORR activity was comparable to those of oxychlorides. Further discussion about ORR pathway of Sr2Co1 − x Fe x O3Cl, and oxygen electrocatalysis of other mixed-anion perovskites will be provided at the conference.Figure 1. H2O2 decomposition rates of Sr2Co1 − x Fe x O3Cl powders.

“The Fe Effect”: A review unveiling the critical roles of Fe in enhancing OER activity of Ni and Co based catalysts

Electrocatalytic oxygen evolution reaction (OER) catalyzed by non-precious metals and their compounds in alkaline medium is an attractive area of energy research for the generation of hydrogen from water. The 3d transition metals, particularly, Ni and Co show better OER activity than others in alkaline medium. Ni and Co based oxygen-evolving catalysts (OECs) experience an enormous enhancement in the OER activity either by incidental or intentional Fe doping/incorporation. To account for this, different roles of Fe that it exerts when incorporated into these OECs are reported to be responsible. Unfortunately, the conclusions drawn in many related studies are often contradictory to one another. Important contradictory conclusions are: 1) a few studies claim Fe is the active site and Ni/Co are inactive while other studies claim Ni/Co and Fe act together in OER, 2) a few studies claim Fe3+ stays unoxidized while a few shows evidence for the existence of Fe4+, and 3) a few studies suggest Fe3+ is the faster site in Ni/Co OEC matrices for OER but fail to explain similar effects observed with other OER matrices. Many critical experimental and theoretical investigations have been made recently to reveal this magical Fe effect and the results of those studies are coherently presented here with critical discussion. This review is presented as it is inevitable to know the critical roles of Fe effect in Ni/Co based OECs to succeed in energy efficient hydrogen generation in alkaline medium.

On the dramatic increase with chain length of the oxidazability of linear saturated aliphatic alcohols on gold in alkaline media

The electrooxidation of linear saturated aliphatic alcohols from C1 to C8 on gold in alkaline media has been studied by cyclic voltammetry and with an electrochemical quartz crystal microbalance. The current density of alcohol oxidation very markedly increased and, correspondingly, the onset potential decreased, with increasing chain length, that is, with initially slightly increasing, and then constant, pKa. We attribute this oxidazability increase with chain length to the increasing hydrophobicity of the alcohol. Effectively, a molecular dynamics simulation of the hydration of alcohols and alcoholates shows that the hydrophobicity of the alcohols increases with increasing chain length. The higher activity of gold for the oxidation of organic, and also inorganic (CO), compounds in alkaline media is well known, and should be due to an activation of the gold surface by OH adsorption, and not to a change of the compounds themselves, the (majority) neutral alcohol being the oxidized species both in acid and alkaline media. At the potentials at which 1-heptanol oxidation starts, the mass in both base electrolyte and in 1-heptanol is at a minimum, or nearly so, which shows that water is driven away from the surface of gold prior to the oxidation of both gold and 1-heptanol.

Urea Oxidation on Ni(OH)2 -X(SO4)0.5 x·yH2o / C-PVC Composite Electrodes

The structural and physical properties of α-Ni(OH)2 materials have been studied because the great importance of this compound in catalysis and for the development of high performance devices. Recently, research efforts have been focused on the synthesis of nanostructured nickel hydroxide with several morphologies [1]. It has been reported that electrodes modified with nickel species present a strong electrooxidation activity in front of organic compounds in alkaline medium [2].The objective of this work was the preparation of nanostructured Ni(OH)2 -x(SO4)0.5 x·yH2Oby hydrothermal method and their characterization by XRD, IR, AFM and SEM. These nanopowders of nickel hydroxide were supported on C-PVC composite electrodes for their electrochemical characterization by cyclic and differential pulse voltammetry.The Ni(OH)2 -x(SO4)0.5 x·yH2O/C-PVC electrode showed good eletrocatalytic activity in the oxidation of urea and high anodic current was observed during the reverse scan (Figure 1). Figure 1.Electrocatalytic response of Ni(OH)2 -x(SO4)0.5 x·yH2O/C-PVC electrode in absence (a) and presence of urea (b) in alkaline medium.

One‐ and Two‐dimensional High‐performance Thin‐layer Chromatography as an Alternative Analytical Tool for Investigating Polyphenol–Protein Interactions

Polyphenols and simple phenolic compounds are able to react with other food constituents during processing and storage. In the past, it has been shown that their reaction with proteins can lead to changes of the technofunctional or even physiological properties of both compound classes. However, identification of specific binding sites of small molecules within a protein sequence (and the corresponding conformational position) is still challenging. Investigating the reaction between different food proteins and phenolic compounds in alkaline medium with one- and two-dimensional high-performance thin-layer chromatography (HPTLC) coupled to matrix-assisted laser desorption/ionisation (MALDI) with time-of-flight (TOF) MS for analysing the peptide profiles after tryptic digestion. After modification with phenolic compounds, protein derivatives were digested and peptides were separated with one- and two-dimensional HPTLC. Peptide profiles were detected with visible and UV wavelengths as well as with fluorescamine, ninhydrin and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid staining. In order to perform mass spectrometric measurements, peptides separated in the first dimension were analysed by MALDI/TOF/MS. Results show that the phenolic acids applied in this study show different specificity and susceptibility when modifying proteins resulting in changes of the peptide profiles, peptide quantity, polarity, UV-activity, radical-scavenging activity and molecular mass. One- and two-dimensional HPTLC supported by mass spectrometric detection represents an innovative, alternative tool for investigating and understanding polyphenol-protein interactions. This approach enables the identification of binding sites inside the protein chain and contributes to understanding the mechanism of polyphenol-protein interactions in vitro and in vivo.

Application of an in situ plated lead film electrode to the determination of organic compounds in alkaline media

In this article, for the first time the possibility of the application of an in situ plated lead film electrode to adsorptive stripping voltammetric determinations of organic compounds at alkaline conditions, to pH of 13.3 was showed. As an example of the application of such electrode a procedure for disopyramide determination by adsorptive stripping voltammetry was elaborated. In non-deaerated solutions of ammonium buffer and sodium hydroxide, an in situ plated lead film electrode exhibited well-developed stripping voltammetric signals for disopyramide. For stabilization of Pb(II) at mild alkaline conditions, potassium sodium tartrate was added to an ammonium buffer used as a supporting electrolyte. The proposed voltammetric procedure was applied to disopyramide determination in pharmaceutical formulation.

Synthesis and Antimicrobial Properties of New Thiosemicarbazide, 1,2,4-Triazole, and 1,3,4-Thiadiazole Derivatives of Sulfanylacetic Acid

1,2,4-triazole and 1,3,4-thiadiazole derivatives are still considered a viable lead structure for the synthesis of more efficient antimicrobial agents having a broad spectrum of activity. This study presents the synthesis and antimicrobial evaluation of a new series of substituted 1,2,4-triazole and 1,3,4-thiadiazole derivatives. Reaction of 4-phenyl-5-(pyridin-3-yl)-4H-1,2,4-triazole-3-thione with ethyl bromoacetate yields the corresponding ethyl acetate (1). In the subsequent reaction with 100% hydrazine hydrate, the hydrazide (2) was obtained, which was converted with isothiocyanates to new acyl derivatives of thiosemicarbazide (3a–l). The cyclization of these compounds in alkaline media resulted in the formation of new derivatives of 1,2,4-triazole (4a–i), whereas in acidic media new derivatives of 1,3,4-thiadiazole (5a,b,g) were obtained. All synthesized compounds were screened for their in vitro antimicrobial activities.

Synthesis and antimicrobial and pharmacological properties of new thiosemicarbazide and 1,2,4‐triazole derivatives

AbstractReaction of 4‐phenyl‐4H‐1,2,4‐triazole‐3‐thione with ethyl bromoacetate has led to the formation of ethyl [(4‐phenyl‐4H‐1,2,4‐triazol‐3‐yl)sulfanyl]acetate 1, the structure of which was confirmed by X‐ray analysis. In the next reaction with 80% hydrazide hydrate, appropriate hydrazide 2 was obtained, which in reaction with isothiocyanates was converted to new acyl derivatives of thiosemicarbazides 2, 3, 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h. The cyclization of these compounds in alkaline media has led to formation of new derivatives of 5‐{[(4‐phenyl‐4H‐1,2,4‐triazole‐3‐yl)sulfanyl]methyl}‐4H‐1,2,4‐triazole‐3(2H)‐thiones 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4j. The structure of the compounds was confirmed by elementary analysis and IR, 1H‐NMR, 13C‐NMR, and MS spectra. Compounds 2, 3, 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h and 4a, 4b, 4c, 4d, 4e, 4f, 4g were screened for their antimicrobial activities, and the influence of the compounds 4a, 4b, and 4e, 4f, 4g on the central nervous system of mice in behavioral tests was examined. J. Heterocyclic Chem., (2011).

Synthesis and antinociceptive activity of 4,4′-bis(1-substituted-semicarbazidyl)diphenylmethane and 4,4′-bis(5-substituted-2,4-dihydro-3-oxo-3H-1,2,4-triazol-4-yl)diphenylmethane derivatives

AbstractIn the reaction of 4,4′-diphenylmethane diisocyanate with carboxylic acid hydrazides, 4,4′-bis(1-substituted-semicarbazidyl)diphenylmethane derivatives were obtained. Depending on their chemical nature, cyclization of these compounds in alkaline medium led to the formation of two groups of compounds: bis(2,4-dihydro-3H-1,2,4-triazol-3-one) derivatives or carboxylic acids. The pharmacological effects of the selected compounds on the central nervous system in mice were investigated. Strong antinociceptive properties of some derivatives, at a wide range of doses, were observed.Graphical abstract[IMAGE]

Studies of some electron transfer reactions of bis(dihydrogentellurato)- argentate(III) : A kinetic and mechanistic approach

The review by Lancashire l on silver is devoted to a small section on kinetics and mechanistic aspects. Since then a great deal of work has been done on kinetics and mechanism of oxidation of different reducing substrates by silver(III) complexes. The present review deals with studies on some electron transfer reactions involving biS(dihydrogentellurato)argentate(III) and 37 reducing organic compounds in alkaline medium which focuses on investigations during the period 1992-2006. The reactions have been carried out under different experimental conditions. Kinetic results and activation parameters of different redox processes have been incorporated and analyzed. The reduction of silver(III) may occur by either one electron or one step two electron transfer process. Although the oxidations appear to proceed through outer-sphere electron transfer process in the rate determining step, the reduced species of silver(II) ultimately decomposes to give black silver compounds. Attempts have been made to compare the results obtained earlier with the oxidations of similar substrates by bis(dihydrogentellurato)cuprate(III).

Amperometric detection of sulfur-containing compounds in alkaline media.

A copper-based chemically modified glassy carbon electrode (GC-Cu) was developed to be used as an amperometric sensor for electrochemically detecting several sulfur-containing compounds in alkaline media. Under optimised flow injection conditions the calibration curves for sulfite, sulfide, thiosulfate, cysteine, cystine, etc., were linear over three orders of magnitude of concentration. Detection limits were of the order of 0.04-1.5 microM. A simple and rapid method for determining sulfite in red and white wines by anion-exchange chromatography with electrochemical detection is described.

Spectrofluorimetric determination of nitrite with 5,6-diamino-1,3-naphthalene disulfonic acid

A simple, sensitive and specific spectrofluorimetric method for the determination of nitrite has been developed. It is based on the selective reaction of nitrite with 5,6-diamino-1,3-naphthalene disulfonic acid (DANDS) in acidic medium to form 1-[H]-naphthotriazole-6,8-disulfonic acid, a highly fluorescent compound in alkaline medium. The linear calibration range for nitrite was 0.8–112 ng ml −1 with a 3 σ detection limit of 0.09 ng ml −1, lower than those of other spectrofluorimetric methods. The proposed method has been applied to the determination of nitrite in tap water (33 ng ml −1) and lake water (17 ng ml −1) without extraction, with R.S.D. ( n=6) of 1.7 and 4.9%, respectively and recoveries of 98–102%.

Flow-injection spectrophotometric determination of adrenaline and dopamine with sodium hydroxide

A new, rapid and economical flow-injection method for determining adrenaline and dopamine is proposed on the basis of the hydrolysis of these compounds in alkaline medium. The method was optimized by using a spectrophotometer operating at λ = 390 nm as detector. Calibration graphs were linear up to 2 × 10 −4M with quantification limits of 2.5 × 10 −6M and 3.3 × 10 −6M for dopamine and adrenaline respectively. Flow-injection allows the measurement of 130 samples per hour. The method was successfully applied for the determination of catecholamines in pharmaceuticals.

Electrochemical detectors - tailormade techniques for liquid chromatography and capillary electrophoresis?

Electrochemical detectors for liquid chromatography and capillary electrophoresis are reviewed with special emphasis on electrode materials that allow the amperometric detection of otherwise non-electroactive compounds such as aliphatic alcohols, carbohydrates or amino acids. Noble metal electrodes can catalyze the oxidation of aliphatic compounds in alkaline media if multistep potential-time waveforms are employed. Various metal and metal oxide electrodes such as Ni, Cu or Co allow the detection of carbohydrates and similar compounds under constant potential conditions. Metallic copper electrodes operating in an amperometric mode or in a potentiometric mode can also serve as selective detectors for complexing species. A range of applications in combination with chromatography and electrophoresis is summarized. The current state of electrochemical detectors indicates that both amperometric and potentiometric detectors are on the verge of becoming tailormade detectors for micro-separation techniques.

How to achieve long-term electrochemical cycling stability with hydride-forming electrode materials

The long-term electrochemical cycling stability of AB5-type compounds in alkaline media can be improved either by lowering the specific surface area of the applied hydride-forming powder or by lowering the oxidation rate constant of the intermetallic compound. Both parameters are shown to be intrinsic material properties. Reducing the specific surface area can be accomplished by making use of non-stoichiometric compounds in which the A-type atoms in the crystal lattice are partly replaced by dumbell pairs of B-type atoms. Electrochemically stable non-stoichiometric compounds are characterized by the absence of a clear discrete α-to-β phase transition upon hydridization, through which particle size reduction of the powder during electrochemical activation remains limited. Compounds with a composition close to or above the as-denoted “critical composition” meet this requirement. On the other hand, lowering the oxidation rate constant can successfully be achieved by replacing part of the A-type atoms by other lanthanides and/or part of the B-type atoms by other transition metals within the AB5 stoichiometry. This leads to so-called multicomponent compounds. Although the hydride-formation/decomposition reaction mechanism for this type of compound is shown to be accompanied by a pronounced discrete phase transition, a relatively low oxidation rate constant ensures a good overall electrochemical cycling stability.

This research contribution is in commemoration of the life and science of I. M. Kolthoff (1894-1993). Pulsed electrochemical detection at the ring of a ring-disk electrode applied to a study of amine adsorption at gold electrodes

Results are shown for application of a Au-Au rotated ring-disk electrode to an investigation of the adsorption and desorption of model organic the compounds in alkaline media. Aliphatic amines are not detected at constant potential, and therefore, a multistep potential five form is applied at the ring electrode to achieve their pulsed electrochemical detection. On the basis of the ring-disk results, the potential-dependent nature of amine adsorption and desorption at the Au disk electrode is easily evaluated. Furthermore, the significance of this information is demonstrated for the optimization of a PED wave form applied for the detection of aliphatic amines separated by high-performance liquid chromatography. Proper choice of the potential for oxide reduction in the PED wave form allows for simultaneous preadsorption of amine compounds with the benefit of enhanced detection sensitivity