Search

Oxygen solubility in a series of binary austenitic Fe-Ni alloys has been measured at temperatures of 1000–1150 °C, under oxygen partial pressures corresponding to the Fe/FeO equilibrium. Oxygen activities controlled in Rhines packs or by flowing CO/CO2 gas mixtures yielded the same results within measurement uncertainty, showing that carbon has no effect at the levels used. The oxygen solubility dependence on Fe-Ni alloy composition is non-ideal, being strongly destabilised by the addition of nickel. Wagner's classical solution model is shown to represent the results well.

Pt is usually not considered as an efficient catalyst for water oxidation. Here, we report a design-of-experiment approach for modelling the roughness of an electrochemically roughened Pt electrode for water oxidation. The results indicate significant interaction between oxidation and reduction potentials on surface roughness and the porous Pt exhibits greatly improved catalytic activity for oxygen evolution in acid which is comparable to the benchmark catalyst RuO₂.

A new design for a membrane-free gas sensor modified with a thin layer of ionic liquid is described. The new approach uses miniaturized interdigitated microelectrodes for detecting gases having reversible electrochemistry, for example, dioxygen. Analyte molecules are reduced on the first working electrode, creating an intermediate species (e.g., superoxide, O2•–, from dioxygen) that can be reoxidized back to the original molecule at the second working electrode. The loop of redox reactions enhances the measured current, leading to high sensitivity (3.29 ± 0.06 nA cm–2 ppm–1) and low detection limit (LOD = 174 ppm). The gas sensor design was demonstrated to monitor typical concentrations of oxygen with good accuracy and precision. The enhancement in the current is characteristic only of gas molecules with reversible electrochemistry, which indicates that the proposed gas sensor can analyze these molecules with greater sensitivity over those with irreversible electrochemistry.

Platinum electrodes have been electrochemically roughened (roughness factors up to 430) and evaluated for use as neural stimulation electrodes. The roughened electrodes show superior interfacial properties with increasing surface roughness. The roughened electrode (fR = 250) has a charge injection limit of 1.0 mC cm(-2) (400 μs pulse width), which is superior to that of titanium nitride (0.87 mC cm(-2)) but comparable to that of carbon nanotubes (1.0-1.6 mC cm(-2)). The surface roughness can also be optimized for different neural stimulation applications based on the available charge density at a particular pulse width of stimulation. The roughened platinum electrodes demonstrated good mechanical stability under harsh ultrasonication and electrochemical stability under continuous biphasic stimulation, indicating the potential of this biological interface to be safe and stable.

We report a systematic study of the effects of types and positions of amino acid residues of tripeptides on the formation constants logβ, acid dissociation constants pKa, and the copper coordination modes of the copper(II) complexes with 27 tripeptides formed from the amino acids glutamic acid, glycine, and histidine. logβ values were calculated from pH titrations with l mmol L(-1):1 mmol L(-1) solutions of the metal and ligand and previously reported ligand pKa values. Generalized multiplicative analysis of variance (GEMANOVA) was used to model the logβ values of the saturated, most protonated, monoprotonated, logβ(CuL) - logβ(HL), and pKa of the amide group. The resulting model of the saturated copper species has a two-term model describing an interaction between the central and the C-terminal residues plus a smaller, main effect of the N-terminal residue. The model supports the conclusion that two copper coordination modes exist depending on the absence or presence of His at the central position, giving species in which copper is coordinated via two or three fused chelate rings, respectively. The GEMANOVA model for pKamide, which is the same as that for the saturated complex, showed that Gly-Gly-His has the lowest pKamide values among the 27 tripeptides. Visible spectroscopy indicated the formation of metal-ligand dimers for tripeptides His-His-Gly and His-His-Glu, but not for His-His-His, and the formation of multiple ligand bis compexes CuL2 and Cu(HL)2 for tripeptides (Glu/Gly)-His-(Glu/Gly) and His-(Glu/Gly)-(Glu/Gly), respectively.

Time of flight secondary ion mass spectrometry (ToF-SIMS) has been used to determine the extent of surface modification of highly ordered pyrolytic graphite (HOPG) samples that were exposed to radio-frequency methane and hydrogen plasmas. The ToF-SIMS measurements were examined with the multivariate method of principal component analysis (PCA), to maximise the amount of spectral information retained in the analysis. This revealed that the plasma (methane or hydrogen plasma) modified HOPG exhibited greater hydrogen content than the pristine HOPG. The hydrogen content trends observed from the ToF-SIMS studies were also observed in elastic recoil detection analysis measurements. The application of the ToF-SIMS PCA method also showed that small hydrocarbon fragments were sputtered from the hydrogen-plasma-treated sample, characteristic of the formation of a plasma-damaged surface, whereas the methane-plasma-treated surface sputtered larger hydrocarbon fragments, which implies the growth of a polymer-like coating. Scanning tunnelling microscopy measurements of the modified surfaces showed surface features that are attributable to either etching or film growth after exposure to the hydrogen or methane plasma.

The semiconducting perovskite oxide, La0.5Sr0.5CoO3, is a catalyst for the reduction of sulphur dioxide by carbon monoxide. Unlike aluminia-supported metal catalysts, La0.5Sr0.5CoO3 tolerates high levels of oxygen in the gas stream if sufficient carbon monoxide is present to react with all the oxygen. Water vapour (2%) does not adversely affect the reaction; unwanted byproducts H2S and COS are reduced for contact times less than 0.25 s. A computer model is used to predict equilibrium gas compositions for systems containing oxygen and water vapour. During the reaction the catalyst itself reacts with sulphur producing metal sulphides, possibly of simple cubic structure. The perovskite sulphides LaCoS3 and La0.5Sr0.5CoS3 are theoretically unstable.

Liquid crystal templating has been used to produce metal films with nanometer-sized pores. While successful templating procedures have been reported for metals from some groups of elements (e.g., groups 9 and 10), no such reports are available for other groups. This work investigates liquid crystal templating procedures for metals from groups 11 and 12. TEM indicates that permanent mesoporous structures are obtained for templated cadmium while copper forms mesoporous structures only temporarily. Silver, gold and zinc could not be templated at all. Reasons for these observations are briefly discussed, underlining the importance of various factors influencing the templating process.

This paper reports a study of the factors affecting the analytical performance of gold and glassy carbon electrodes modified with the tripeptide Gly-Gly-His for the detection of copper ions. Gly-Gly-His is attached to a glassy carbon (GC) surface modified with 4-carboxyphenyl moieties or a gold surface modified with 3-mercaptopropionic acid by the reaction of the N-terminal amine group of the peptide with the carboxylic acid groups of the monolayer via carbodiimide activation. X-ray photoelectron spectroscopy was used to characterize the steps in the biosensor fabrication. It was found that the analytical performance of a sensor prepared with Gly-Gly-His on a GC electrode was similar to that on a gold electrode under the same conditions. The performance was greatly enhanced at higher temperature, no added salt during copper accumulation and longer accumulation time within a pH range of 7 – 9. Interference studies and investigations of stability of the Gly-Gly-His sensor are reported. Analysis of natural water samples show that the sensors measure only copper ions that can complex at the sensor surface. Strongly complexed copper in natural water is not measured. Despite greater stability of diazonium salt derived monolayers on carbon surfaces compared with alkanethiols self-assembled monolayers on gold, the stability of the sensors was essentially the same regardless of the modification procedure.

This paper studies the analytical performance and characterization of a peptide modified biosensor towards detection of Cu2+ ions. The peptide modified biosensor is developed by carbodiimide attachment of the Gly-Gly-His tripeptide onto a 3-mercaptopropionic acid (MPA) modified gold surface. X-ray photoelectron spectroscopy (XPS) was used to characterize the steps in the biosensor fabrication. Detection of Cu2+ ions are determined by cyclic and Osteryoung square wave voltammetry. The analytical performance of this biosensor is found to be affected by the pH, salt concentration, temperature and accumulation time of the test solution. Interference studies and investigations of the reusability of this biosensor have also been performed.

An electrochemical sensor for cadmium ions is described which is made by modifying a gold electrode with 3-mercaptopropionic acid followed by covalently coupling the cadmium-selective hexapeptide His–Ser–Gln–Lys–Val–Phe. The resultant electrode had significantly superior analytical performance compared with a glutathione (GSH) modified electrode for the detection of Cd2+, having a greater sensitivity, broader detectable concentration range and a five times lower detection limit of 0.9 nM. Interference from Pb2+ was observed which is an improvement from the GSH modified electrode which had Pb2+ and Cu2+ as interfering ions. The effects of Cu2+, Ni2+, Zn2+, Cr3+ and Ba2+were insignificant. Keywords: Heavy metals, Biosensors, Electrochemistry, Cadmium, His–Ser–Gln–Lys–Val–Phe, Glutathione

Electrochemical sensors for copper ions in environmental samples were prepared by modifying gold electrodes with l-cysteine by self-assembly. The adsorption of l-cysteine on gold electrodes was studied by electrochemical reductive desorption in 0.5 M KOH, and the interaction of l-cysteine with copper ions was investigated by cyclic voltammetry, chronoamperometry and X-ray photoelectron spectroscopy. At low concentrations the ratio of l-cysteine to bound Cu(II) is 2:1. At higher concentrations (0.1 M) copper reacts with adsorbed cysteine forming copper sulfide on the electrode surface. On a modified l-cysteine gold electrode, Osteryoung square wave voltammetric determination of Cu(II) with a detection limit below 5 ppb has been demonstrated.

Amino acids and peptides are known to bind metal ions, in some cases very strongly. There are only a few examples of exploiting this binding in sensors. The review covers the current literature on the interaction of peptides and metals and the electrochemistry of bound metal ions. Peptides may be covalently attached to surfaces. Of particular interest is the attachment to gold via sulfur linkages. Sulfur-containing peptides (eg cysteine) may be adsorbed directly, while any amino group can be covalently attached to a carboxylic acid-terminated thiol. Once at a surface, the possibility for using the attached peptide as a sensor for metal ions becomes realised. Results from the authors’ laboratory and elsewhere have shown the potential for selective monitoring of metal ions at ppt levels. Examples of the use of poly-aspartic acid and the copper binding peptide Gly-Gly-His for detecting copper ions are given.

The electrochemistry of platinum electrodes in artificial perilymph solution subjected to cyclic and steady-state potentials was studied by a quartz crystal electrochemical microbalance and by analysis of electrolyte for dissolved platinum. The effect of amino acid adsorption appears to be one of blocking sites for platinum oxidation and oxide reduction, a process in which the amino acid competes with chloride from phosphate-buffered saline. For amino acids such as cysteine, which are known to interact strongly with platinum, the voltammograms became nearly featureless and only a small change in mass was observed during cycling of the potential. There were no mass changes of an electrode in solution containing human serum albumen, but its presence did inhibit dissolution of platinum. The overall magnitudes of dissolved platinum found in the buffered solutions were low, remaining below 5 ppb in most cases. Dissolution was greatest in solutions containing high concentrations of cysteine. Extrapolation of the results to implanted auditory prosthesis electrodes indicated that platinum dissolution would not lead to toxic concentrations in the body.

The determination of free cadmium ions with solid-state cadmium ion-selective electrode can be performed in non-flow measurements in non-buffered solutions in a wide concentration range down to pCd 10. In cadmium ion buffered solutions linear Nernstian response was obtained even down to pCd 12, which is lower, that expected based on calculation of cadmium solubility from the conditional solubility product. Interferences of trace amounts of Fe(III), Cu(II) and Pb(II) commonly present in natural waters in larger concentrations than Cd(II) can be eliminated by reduction with hydroxylamine, complexation with Neocuproine and ion-exchange on anion-exchange resin in sulphate form, respectively. The developed procedure might be suitable for the determination of activity of free cadmium ions in natural water. A preliminary study on this subject is demonstrated for river water sample using stopped-flow flow-injection system.

Lead(II)-selective PVC membrane electrodes based on 4,7,13,16-tetrathenoyl-1,10-dioxa-4,7,13,16-tetraazacyclooctadecane (TTOTC) as ionophore were prepared. The optimum composition of the membrane was 30 wt% poly(vinyl chloride), 67 wt% 2-nitrophenyl octyl ether plasticizer, 3 wt% ionophore with added lipophilic salt potassium tetrakis( p-chlorophenyl)borate at 50 mol% with respect to the ionophore concentration. The electrodes exhibited near theoretical Nernstian slopes (31.9 ± 0.4 mV/per decade) in the activity range log10[a(Pb2+)] = −5.3 to log10[a(Pb2+)] = −3.0 and with a detection limit log10[a(Pb2+)] = −5.7. Compared to the previously reported disubstituted, diazacrown 7,16-dithenoyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane the electrodes based on TTOTC showed much better selectivity particularly towards alkali and alkaline metal ions. However, mercury and silver remain the major interferences. The electrodes were used in potentiometric titrations of Pb2+ and the determination of Pb2+ in synthetic soil samples.

Three flow injection systems with potentiometric detection have been developed for speciation of fluoride using a fluoride ion-selective electrode with a single flow-through detector. Among systems with (i) splitting of the sample zone and confluence point, (ii) flow reversal and (iii) resampling, the latter was most suitable. Its application was demonstrated for a study of the effectiveness of releasing fluoride from complexes with Al(III). Several ligands were examined as decomplexing agents such as EDTA, cyclohexane-1,2-diamine-N,N,N′,N′tetraacetic acid (DCTA), citrate and 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt (Tiron). In flow injection measurements, only Tiron was found suitable for decomposition of Al(III)–fluoride complexes. In stopped-flow measurements, it was observed that with use of citrate or DCTA about a 10 min delay was required to release fluoride from Al(III) complexes. A flow-injection system with resampling was also utilised for speciation of calcium with ion-selective electrode in ligand solutions and in natural waters.

Nonactin and N,N-dioctadecylmethylamine ionophores, each in an epoxydiacrylate polymer, were photo-cured on silver wires (0.8 mm i.d.) and evaluated as ammonium and hydrogen (pH) coated wire electrodes. The photo-cured membranes prepared in this study exhibited excellent adhesion to the metal substrate and improved mechanical strength compared to PVC based membranes. The ammonium electrode exhibited a Nernstian response over a concentration range between 0.01 mM and 100 mM with a detection limit of 0.0005 mM. The ammonium electrode exhibited improved selectivity against most common interfering ions, including potassium compared to previous studies. The hydrogen selective electrode exhibited a near-Nernstian slope of 55.9± 0.8 mV change/log a(H+) between pH 4.0 and pH 11.0 in the steady-state mode. The ammonium and pH sensors each responded quickly reaching 90 % of steady-state value in < 5 s, making these coated wire sensors ideal for flow injection potentiometry measurements. In the FIP mode, both the photo-cured ammonium and pH electrodes exhibited near-Nernstian responses of 49.2 ± 1.0 mV change / activity decade and 50.2 ± 0.4 mV change / log a(H+), respectively, over a similar concentration range as in the steady-state mode. The photo-cured ammonium and pH electrodes were used simultaneously in the analysis of hydroponic nutrient solutions and waste water samples obtained from a local greenhouse grower in the flow injection potentiometric mode.

A potassium ion selective electrode (ISE) is reported based on the epoxyacrylate polymer prepared from o-nitrophenyl octyl ether as the plasticizer and 2,2′-bis [3,4-(15-crown-5-)-2-nitrophenylcarbamoxymethyl]tetradecane (BME-44) as the ionophore. Several different electrodes were studied by photo-curing different membranes onto a silver wire (0.8 mm i.d.), and the response characteristics were evaluated. The membranes prepared exhibited strong adhesion to the metal substrate and showed improved mechanical strength compared to poly(vinyl chloride)-based membranes. The sensor exhibited Nernstian response over a log-linear range of between 0.01 mM and 100 mM, and was selective against the common interfering ions. Fast response reaching 90% of steady-state value in 5 s makes this sensor applicable for flow injection potentiometry measurements. The potassium ISE allows for accurate determinations of potassium in various water samples by flow injection potentiometry.

The illicit drug methylamphetamine is often prepared from the precursor ephedrine or pseudoephedrine, which in turn are obtained by three processes: extraction from the Ephedra plant ("natural"), via fermentation of sugars ("semi-synthetic"), and by a "fully synthetic" route from propiophenone. We report the first method to differentiate between the three industrial routes used to produce the precursors ephedrine and pseudoephedrine by measurement of stable isotope ratios of nitrogen (δ15N), hydrogen (δ2H), and carbon (δ13C). Analysis of 782 samples of seized methylamphetamine allowed classification into three groups using k-means clustering or the expectation-maximization algorithm applied to a Gaussian mixture model. By preparation of 30 samples of ephedrine by the "fully synthetic" industrial process and measuring their δ15N, δ2H, and δ13C values, we observed that 15N becomes significantly depleted compared to the methylamine starting material. Conversion of ten ephedrine samples to methylamphetamine showed that this depletion is maintained in the final drug product, of which the δ15N, δ13C, and δ2H values were distinct from those of ephedrine and methylamphetamine samples of a semi-synthetic (fermentation pathway) origin. Combining modeling analysis with the new experiments and published information on the values of δ2H gave a definitive assignment of the three model groups, and equations to obtain probabilities for the precursor origin of any new sample. A simple rule of thumb is also presented. Making an assignment using delta values is particularly useful when no other chemical profiling information is available. © 2013 American Chemical Society.

The amperometric determination of thiols by injection into a mercury carrier stream is shown to be a sensitive method when using a tungsten wire as the working electrode in a three-electrode flow cell. Hg2+ gives sharp peaks when injected into phosphate buffer at pH 3.1 at an operating voltage of -0.24 V (against a Ag/AgCl reference electrode). Hg2+ was determined in the range 0.43 to 25.0 μM with linear response. Injection of cysteine into the mercury carrier causes a decrease in the cathodic current, and sharp flow injection peaks are observed with a peak width of approximately 60s. Optimization of various parameters was performed, including buffer effects, mercury concentration, injection volume, and the effects of various cations and anions on the response were determined. Linear calibrations in the range 0.25 μM to 100 μM for cysteine and 1.3 to 1000 ng for the other thiols glutathione, thiourea, albumin, and DNA were found. The responses to cysteine and thiourea were most sensitive, and interference from silver and iodate was observed at concentrations in excess of the thiols. The method may be used as a rapid means of detecting thiols in various samples and as an HPLC detection method.

Electrolysis of copper(II) sulfate solutions in a radial quasi-two-dimensional thin cell showed typical tree-like morphologies of the copper deposit when low concentrations of a supporting electrolyte of sodium sulfate were added. When the concentration of sodium sulfate was one-tenth that of the copper(II) sulfate a small tree-like copper deposit surrounded by a blue ring was observed. With greater concentrations of sodium sulfate a continuous blue disc was observed which turned brown as the experiment proceeded. X-ray diffraction patterns revealed the deposit to be copper(II) oxide. It is proposed that this forms from an initial hydrogel of copper(II) hydroxide. A maximum in the current may correspond to the deposition of a concentrated outer ring of copper(II) hydroxide.

Flow analysis data of the response of an aluminum wire electrode to fluoride into which Al3+ is added is modeled assuming a logarithmic response of the electrode to F− and reaction of F− with aluminum ions to give a series of complexes [AlFq](3−q)+ when q = 1,2,3,4,5,6. The solutions were maintained at pH 5.0 with acetic acid/acetate buffer. Other species modeled were the hydroxo complexes of aluminum [Alm(OH)n](3m−n)+ when m = 1, n = 1,2,3,4; m = 2, n = 2; m = 3, n = 4; m = 13, n = 32, and the acetate complex [Al2(OH)2OAc]3+. Protonation of F− to HF and HF 2− was also considered. Three coefficients were required to fit the data, a constant and slope of the response of the electrode to free fluoride and a dispersion factor in the flow analysis. Published stability constants were used and no account was taken of ionic strength. The model may be used to predict optimum analysis conditions given an approximate aluminum concentration. Copyright © 1995 VCH Verlagsgesellschaft mbH

Copper, zinc, silver and palladium were grown in supports of filter-paper, glass-fibre, nylon membrane and polypropylene membrane. The support has a great effect on both the macroscopic and microscopic habit of the deposits. It was difficult to plate metals from solutions containing completing agents (e.g., cyanide, EDTA) that give anionic metal species. Brighteners and levellers that change the grain size of the deposit also affect the overall morphology. It is clear that the chemical nature of the electrolyte and the support is a major determining factor in the form of the growth.

This paper investigates the comparison of glassy carbon to that of thin carbon films as electrode substrates. It is observed that the modification of the carbon surfaces, via the electrochemical reduction of aryl diazonium salts to the surface, occurs on both substrates in a similar fashion. Subsequent modification of the substrates with the peptide Gly-Gly-His attached to the bound layer, shows that both surfaces can be used in the detection of copper (II) in water solutions and at pH 7.

The theory is developed of the voltage of several cells connected in series that have an electrolyte bridge between each cell. The measured voltage increases as the ratio of the electrolyte resistance between cells to that within each cell is increased. Experiments with half cell compartments with platinum and silver electrodes in 0.001 mol dm−3 potassium permanganate solution connected by thin tubes of different lengths showed a fit to theory if a small constant resistance was included.

Parallel factor analysis (PARAFAC) was used to analyze data from the high throughput screening of an array of organometallic rhodium and iridium complexes as catalysts for the intramolecular hydroamination of 2-(2-phenylethynyl)aniline to give 2-phenylindole. The progress of the hydroamination reactions was monitored using UV-visible spectroscopy. The overlapped UV-visible spectra of the mixture of starting material, product and solvent in the samples taken at different times were deconvoluted using PARAFAC. Unique PARAFAC models led to close approximations of the actual UV-visible spectra of the compounds in the mixture. The performance of the catalysts was then compared by estimating the final concentration of the starting material and product using PARAFAC loadings. A library of 63 complexes generated in situ was examined in a single experiment using this methodology. The complexes were generated from combinations of seven ligands (bis(N-methyl2-imidazolyl)methane, bis(1-pyrazolyl)methane, 1,10-phenanthroline, N,N'-bis(p-tolyl)diazabutadiene, N,N'-bis(p-tolyl)1,2-dimethyldiazabutadiene, N,N'-bis(mesityl)1,2-dimethyldiazabutadiene and bis(2,4,6-trimethylphenylimino)acenapthene) and nine metal precursors ([Ir(COD)Cl](2) (COD = 1,5-cyclooctadiene), [Ir(CO)(2)Cl](n), [Ir(COE)(2)Cl](2), [IrCp*Cl(2)](2) (Cp* = 1,2,3,4,5-pentamethylcyclopentadiene), [Rh(COD)Cl](2), [Rh(CO)(2)Cl](2), [Rh(COE)(2)Cl](2), [RhCp*Cl(2)](2) and [RhCpCl(2)](2)) (Cp = cyclopentadiene)). The proposed method can be used for the fast screening of arrays of metal complexes for identifying effective catalysts, providing information that can augment traditional methods used for the analysis of catalyzed reactions.

Series of samples of La1 - x Srx CoO3 - y with x = 0.8, 0.5 and 0.2 have been prepared by calcination at temperatures between 550° and 1150° C of fine powders of mixed nitrates obtained by the spray-freeze/freeze-drying technique. Crystallization of the cobaltites at temperatures as low as 570° C was observed. The X-ray diffraction of calcined samples revealed clearly the existence of superstructures apparently due to vacancy ordering. The type of the crystal cell formed was a function of the composition and of the conditions of preparation. The new phases seem to be metastable.

In acid solutions containing Cu2+ and Br− copper corrodes to copper (I) bromide. After a fast reaction at a clean copper surface the kinetics are parabolic: the rate is inversely proportional to the thickness of the copper bromide film. Both the initial rate and the parabolic rate constant correlate with the concentration of CuBr+ in solution, and not with that of Cu2+ nor Br−. The formation constant of CuBr+ was determined to be 0.71. A model is presented in which CuBr+ is transported through the growing film under concentration and potential gradients. The rate of change of the potential at the corroding metal follows a model based on the Butler-Volmer equation.

Ethanol in wines was determined by flow injection analysis with an amperometric detector using an oxidized nickel wire. Solid-phase extraction with a strong anion exchanger was used to remove interferences such as organic acids from the matrix, and the residue of the extraction was injected directly into the FIA system. The recoveries of ethanol from wines spiked with standards ranged from 101% to 103%. The response of the nickel electrode to ethanol is dependent on the applied potential and the pH of the carrier. The optimal conditions for the detection of ethanol were an applied potential of +0.60 V (vs. Ag/AgCl) in a carrier of 100 mM sodium hydroxide solution. The electrode exhibited a linear response from 10−5 to 10−3 M, with a detection limit of 1 × 10−6 M. The method was demonstrated by the determination of ethanol in wines.

In the previous two chapters we have seen what can be made with electrical energy, reviewing electrochemical synthesis in Chapter 11 and larger-scale industrial processes in Chapter 12. Now the scene is reversed. We are to look at how to make electrical energy from the free energy of an electrochemical reaction. Consider our old friend, the reaction $$ {H_2} + \tfrac{1}{2}{O_2} \to {H_2}O $$ (13.1) which has a standard electrode potential of 1.23 V and so a free energy change of −1.23 × 2 × 96 487 = −237.4 kJ mol−1. (There are two electrons involved in the reaction. If you do not know why, see Chapters 4 and 8.) If you combine 1 mol of hydrogen and ½ mol of oxygen, the reaction releases 237.4 kJ. If you have 237.4 kJ, then you can stick it into water and make 1 mol of hydrogen and ½ mol of oxygen.

Methamphetamine HCl was synthesized using three variations of the hydriodic acid/red phosphorus (HI/Pred) synthetic route. A Plackett-Burman experimental design was used to determine how reaction parameters affected the isotopic composition of the product. Isotope ratio mass spectrometry results showed only the source of precursor 13C was significant in determining product δ 13C; the manufacturer, reaction temperature, time, scale, and source of HI were not significant. The precursor was also the main determinant of product δ 2H, with smaller contributions from the HI source for one method. From precursor to product, large δ 2H depletion occurred for most samples. Deuterium nuclear magnetic resonance spectroscopy (2H NMR) was used to investigate the specific site of this. Significant fraction of deuterium was observed only at the benzylic position, the site of hydrogen addition during synthesis. Methamphetamine synthesized from ephedrine was shown to be depleted in this position.

The simultaneous determination of Cu(2+), Cd(2+) and Pb(2+) is demonstrated at four modified gold electrodes using N-PLS calibration. Three of the electrodes were modified with the peptides Gly-Gly-His, gamma-Glu-Cys Gly and human angiotensin I which were covalently attached to thioctic acid self-assembled monolayers and the fourth electrode was modified with thioctic acid only. Voltammetry at the modified electrodes in the presence of the three metal ions revealed one peak due to the reduction of copper and another due to the overlapping peaks of cadmium and lead which made quantification using conventional methods difficult. N-PLS was used to calibrate and predict trace concentrations (100 nM to 10 microM) of mixtures of Cu(2+), Cd(2+) and Pb(2+).

An electrochemical sensor for the detection of cadmium ions is described using immobilized glutathione as a selective ligand. First, a self-assembled monolayer of 3-mercaptopropionic acid (MPA) was formed on a gold electrode. The carboxyl terminus then allowed attachment of glutathione (GSH)via carbodiimide coupling to give the MPA-GSH modified electrode. A cadmium ion forms a complex with glutathione via the free sulfhydryl group and also to the carboxyl groups. The complexed ion is reduced by linear and Osteryoung square wave voltammetry with a detection limit of 5 nM. The effect of the kinetics of accumulation of cadmium on the measured current was investigated and modeled. Increasing the temperature of accumulation and electrochemical analysis caused an increase in the voltammetric peak of approximately 4% per degrees C around room temperature. The modified electrode could be regenerated, being stable for more than 16 repeated uses and more than two weeks if used once a day. Some interference from Pb(2+) and Cu(2+) was observed but the effects of Zn(2+), Ni(2+), Cr(3+) and Ba(2+) were insignificant.

An amperometric sensor constructed with a metallic tungsten wire is reported for the indirect detection of organic thiols and proteins. Cysteine added to mercury(II) (40.0μM) buffered in 5.0 mM sodium acetate at pH 4.7 causes a decrease in the reduction current of mercury at −0.2 V (vs. SCE). Detection limits were found to be in the range 0.05�"0.2 μg/mL for cysteine, thiourea and glutathione, but were poorer for albumin and DNA, showing this method is relatively selective for cysteine. The advantages of the tungsten electrode are its low cost, miniature size, and its inert oxide surface which does not amalgamate with mercury. Copyright © 1995 VCH Verlagsgesellschaft mbH

Mammalian cochlea perilymph contains amino acids and protein which have a major effect on the electrochemistry of an implanted auditory prosthesis. Cyclic voltammetry in an artificial perilymph solution shows that many amino acids adsorb at the platinum electrode diminishing oxidation of the metal, and also blocking hydrogen evolution. At anodic potentials > 900 mV vs. silver/silver chloride they are oxidized leaving adsorbed oxidation products. The sulfur-containing amino acids cysteine and methionine have the greatest effects. Protein (human serum albumin, HSA) has a similar hut smaller effect. A solution containing HSA (2 mg mL -1 ), phenylalanine (175 μM), glycine (396 μM), and proline (40 μM) in phosphate buffered saline is proposed as suitable artificial perilymph solution having similar electrochemical and adsorption properties to perilymph.

Conducting salts of tetrathiafulvalene (TTF) and a series of oxonol dyes have been prepared electrochemically by the in situ oxidation of TTF in the presence of the anion of the dye. The salt having the greatest conductivity (0.1 Sm−1) is a TTF-N-ethyl hydroxypyridone trimethine oxonol salt. A cyclic voltammetric study of the salts and precursors, electron spin resonnce and photoelectron spectra and the pH dependence of the rest potential are reported. On heating above 150°C the conductivity of the complex and the esr signal decayed, although this is a lower temperature than that at which the complex decomposes (256°C).

Temperature-programmed desorption mass spectrometry (TPD-MS) and thermogravimetric analysis of freeze-dried La1−xSrxCoO3 (x=0.3, 0.5, 0.6, 0.7) on exposure to sulphur dioxide and carbon monoxide was performed for the gases alone and their mixtures. The theory of TPD-MS is presented and the method used to determine activation energies of desorption. The ease of oxygen loss from the catalysts heated in vacuo to 650°C increased withx. Subsequent adsorption of carbon monoxide leads to a further mass loss forx=0.3 but a gain in mass occurs forx=0.7 suggesting strong adsorption at oxygen vacancies. Mass increases were recorded for the adsorption and reaction of sulphur dioxide at 500°C that increased with lanthanum content. Exposure to mixtures of sulphur dioxide and carbon monoxide were accompanied by reaction yielding elemental sulphur, carbonyl sulphide and great increases of mass of the catalyst. The X-ray diffraction patterns of the catalysts after adsorption of carbon monoxide at 500°C showed little change from the perovskite structure. However a mixture of sulphates and sulphides in addition to the underlying perovskite were found after exposure to sulphur dioxide, and for exposure to both gases the original structure was lost and replaced by a mixture of sulphides and oxosulphides of the metals. No perovskite sulphides were detected.

Several workers have studied the properties of adsorbed methanol with a view to elucidating the mechanism of this potentially important fuel cell reaction. It is thought that the rapid adsorption of methanol occurs giving fragments having the formulas COH or COOH and, eventually, CO. The fragment (CHO/sup +/) has been detected after a platinum emitter was exposed to methanol vapor. At potentials below 0.6V (vs. SHE), the slow step in the oxidation is thought to be the reaction of the adsorbed fragment with an adsorbed hydroxyl radical. The work presented here has measured the rates of oxidation of adsorbed methanol at potentials between 0.6 and 1.0V and temperatures between 0/sup 0/ and 40/sup 0/C by a potentiostatic step method and by steady-state current-voltage measurements. The oxidation of fragments from fully deuterated methanol has also been studied.

An electrochemical metal ion sensor has been developed with a detection limit of less than 0.2 ppt by the covalent attachment of the tripeptide Gly-Gly-His as a recognition element to a 3-mercaptopropionic acid modified gold electrode.

A method is described which follows, by mass spectrometry, the kinetics of 18O16O evolution from an electrode surface enriched with 18O. The kinetics on a platinum surface in acid and alkaline electrolyte were consistent with a mechanism of oxygen evolution which involves successive oxidations on a single platinum atom. The total number of platinum sites responsible for oxygen evolution was less than the total number of atoms at the surface.

The kinetics of the electrochemical evolution of deuterium from solutions of sodium sulphate on platinised platinum electrodes enriched with adsorbed deuterons have been fitted to a theoretical model which yielded values for the coverage of deuterium and the total number of surface sites responsible for the reaction. The number of sites agreed with that determined from hydrogen stripping. The kinetics of the removal of adsorbed deuterium on allowing the electrode to stand in air at open-circuit voltage (OCV) were consistent with a second-order recombination with k2= 0.02 s–1 for da/dt=k2a2, where a is the fractional coverage of deuterium at the electrode. The numbers of sites and the volume of deuterium evolved measured for a series of platinised tungsten trioxide electrodes showed spillover of hydrogen from platinum to tungsten trioxide, in agreement with earlier theories.

Copper supported on alumina is a catalyst for the reduction of sulphur dioxide by carbon monoxide. In the presence of water and oxygen, calculation of the equilibrium state of the gas phase and condensed phase by a free energy minimisation method reveals that for certain combinations of gas composition and temperature, copper(II) sulphide will be formed.Copper was converted to copper sulphide when used as a catalyst for the reduction of a stoichiometric mixture of sulphur dioxide and carbon monoxide containing 2.4 % water at 580°C. Oxygen is a poison for the reaction.

The deposition and dissolution of copper from copper sulphate solutions have been studied by galvanostatic measurements. From current overpotential relations it is concluded that the rate limiting step in the electrochemical reduction or oxidation at pH 1 is the reaction Cu2++ e ⇌ Cu+. In the presence of chloride and sulphite ions, the CuCl–2 complex is formed which stabilises the CuI state. The rate limiting step is now the reduction of this complex. Anodically the slow step is the oxidation of CuCl–2.The addition of sulphite ions chemically reduces CuII to CuI, but the rate is much slower than the electrochemical reduction at an overpotential of –100 mV.At pH 1 chemical dissolution of the copper deposited at the cathode occurs.

The kinetics of the electrochemical evolution of 18O16O from NiCo2O4 and LixCo3–xO4(0 < x < 1.5) electrodes enriched with 18O have been studied. The number of sites responsible for oxygen evolution is related to the lithium content of LixCo3–xO4, showing the importance of tetrahedrally coordinated Co3+. NiCo2O4 has different Tafel parameters and a greater number of sites. In this case some participation of Ni2+ and Co2+ is indicated. The data are consistent with a multistep reaction on a single site, or reaction via a bridged structure.