Microcomputer-controlled polarographic instrumentation and its use in the determination of stability constants of crown ether complexes

A computer-controlled polarographic system is described, based on a commercially available polarograph interfaced to a microcomputer. Experiments are controlled and monitored entirely from software, including automatic evaluation of the Tast polarograms and addition of solutions to the polarographic cell from a motor burette. The program was written in FORTH, a computer language especially apt for laboratory automation. The system is used in the determination of stability constants of crown ether complexes

Some Investigations in Theoretical and Experimental Electrochemistry

This thesis is composed of three distinct topics. Chapters II, III and IV are concerned with the analytical consequences of adsorption of reactants at the electrode surface with d.c. polarography and normal and differential pulse polarography. Theoretical behavior was calculated by means of digital simulation and Laplace transform techniques. The effects of nonlinear adsorption isotherms and uncompensated resistance on current-potential response was calculated. The reaction Cd+2/Cd (Hg) with adsorption induced by the presence of iodide was used as a test system. Chapters V and VI are concerned with the electrochemical behavior of molecules with more than one center for electron transfer. Classical statistical methods were used with computer calculation of results, Problems considered include concentration- and current-potential behavior of: (1) polymeric species with no interaction between centers; (2) dimers with interactions; and (3) asymmetric binuclear molecules. Chapter VII discusses data analysis techniques for "large step" coulostatics in the study of electron transfer kinetics. The merits of the technique in electrochemistry are discussed. A method for the use of a numerically generated function as the basis function for nonlinear regression is discussed. Chapter VIII presents a study of alternative methods of "small step" coulostatic data analysis. Strong cross-correlation was found between double layer capacitance, charge transfer parameters and diffusional parameters.</p

The application of neural networks to anodic stripping voltammetry to improve trace metal analysis

This thesis describes a novel application of an artificial neural network and links together the two diverse disciplines of electroanalytical chemistry and information sciences. The artificial neural network is used to process data obtained from a Differential Pulse Anodic Stripping (DPAS) electroanalytical scan and produces as an output, predictions of lead concentration in samples where the concentration is less than 100 parts per billion. A comparative study of several post analysis processing techniques is presented, both traditional and neural. Through this it is demonstrated that by using a neural network, both the accuracy and the precision of the concentration predictions are increased by a factor of approximately two, over those obtained using a traditional, peak height calibration curve method. Statistical justification for these findings is provided Furthermore it is shown that, by post processing with a neural network, good quantitative predictions of heavy metal concentration may be made from instrument responses so poor that, if using tradition methods of calibration, the analytical scan would have had to be repeated. As part of the research the author has designed and built a complete computer controlled analytical instrument which provides output both to a graphical display and to the neural network. This instrument, which is fully described in the text, is operated via a mouse driven user interface written by the author

ANALYTICAL CHEMISTRY DIVISION ANNUAL PROGRESS REPORT FOR PERIOD ENDING NOVEMBER 15, 1963

Research and development progress is reported on analytical instrumentation, chemical analysis of advanced reactor fuels, analytical studies of molten-salt systems, special research problems, reactor projects, effects of radiation on analytical methods, x-ray and spectrochemical analyses, spectroscopy, optical and electron microscopy, nuclear and radiochemical analyses, inorganic preparations, organic preparations, and analytical development. Service analyses are also described. Separate abstracts were prepared for each topic. (M.C.G.

Two new instruments for analytical chemistry: A. Constant potential pulse polarography (CPPP) and differential CPPP (DCPPP) for determination of metals in the presence of oxygen in flowing systems; B. Versatile laser-based analytical instrument for detection of jet-cooled molecular species

Analytical chemistry as a field is composed largely of methods of measurement and analysis. The needs of analytical chemists have developed a complexity which must be matched by the capability of the techniques in use. This calls for the advent of new methods and techniques suitable for the problems at hand. Two new instruments are described in this work which are small steps in meeting some of the complex needs of analytical chemistry;The first instrument represents one of the older analytical methods, polarography, which has been in use in analytical chemistry for over 65 years. Polarography is a method which has seen a decline in use as more sensitive techniques are discovered, but which is still in wide use. The instrument described herein allows polarographic analysis of metals without removal of dissolved oxygen, previously a time-consuming necessity. Detection is accomplished by constant potential pulse polarography (CPPP). The instrument makes feasible detection in flowing samples by elimination of the required oxygen removal step. CPPP further offers a degree of freedom from interference due to reduction of hydrogen ion in acidic solution. The technique is shown to be sensitive, with a detection limit in the range of 10[superscript]-7 M for the metals studied. A differential method has also been developed, differential CPPP (DCPPP), which is shown to have increased selectivity over CPPP, offering resolution on the same scale as differential pulse polarography (DPP);The second instrument described represents one of the newer analytical techniques, supersonic jet spectroscopy. Analytical usage of this method has been only within the current decade, though recent development has been rapid, chiefly due to the immense selectivity resulting from the cooled analytes. The instrument designed for this work was intended to be versatile, allowing sample introduction by gas chromatography (GC) or by laser desorption (LD). Capabilities of the instrument are shown and a method for analysis is given. The detection limit for jet spectroscopy is hampered by the large dilution of sample which is necessary to accomplish the molecular cooling, but was found to be 9 ppm for aniline in Helium carrier gas under optimized expansion conditions for this instrument using multiphoton ionization (MPI)

Kinetic studies in the electrocrystallisation of metals

PhD thesisNone availabl

An Exploration of Basic Processes for Aqueous Electrochemical Production of Hydrogen from Biomass Derived Molecules

Polymer electrolyte membrane fuel cells(PEMFCs) are energy conversion devices with significant potential. The factors preventing them from becoming widespread concern production and distribution of hydrogen. Developing an efficient hydrogen infrastructure with an approachable rollout plan is an essential step towards the future of fuel cells. Water electrolysis is limited by the thermodynamics of the process, which leads to high electrical consumption and significant materials challenges. Alternative methods for cleanly generating hydrogen while using a lower cell voltage are required. PEM based electrolyzers can operate with a depolarized anode , whereby they become significantly less power hungry. This thesis explores two techniques for chemically depolarized electrolyzer anodes. These include a methanol anode and a phosphomolybdic acid anode. To improve the phosphomolybdic acid anode we have characterized the basic electrochemical behavior of phosphomolybdic acid, the anode behavior in a zerogap electrochemical cell, and the biomass oxidation characteristics of several Keggin ions and potential oxidation promoters. The methanol cathode was evaluated using a dynamic hydrogen electrode and shown to be significantly more sensitive to crossover induced voltage losses than was previously reported. Phosphomolybdic acid oxidation kinetics were examined and found to be facile, despite a change in mechanism which occurs after bulk reduction. The temperature dependent diffusion coefficient was found to be on the same order as other likely small, redox active molecules. A previously unreported crossover phenomena was noted and the diffusion coefficient through NAFION was calculated as on the same order as vanadium. The whole cell performance of the phosphomolybdic acid mediated electrolyzer was examined and found to be highly dependent on supporting electrolyte, temperature, and electrode materials. The optimized condition of 5 M HCl and 80 Celsius showed significant improvement in exchange current density, versus the standard conditions of room temperature and no supporting acid, used in the literature. The electrode kinetics have now been removed as a major problem in the system design. While the electrochemical performance of the POM mediated electrolyzer was sufficient, the glycerol oxidation rates were found to be lacking. Vanadium, iron, and hydrochloric acid were the most effective additives; while sulfuric acid decreased reaction rates

Studies on metal α-isosaccharinic acid complexes

This thesis details the experimental work carried out during a three year project commissioned by UK-Nirex. The main objective of the project was further developing the software package STAB, a programme produced at Loughborough University for predicting stability constants. It is intended that the software will be able to predict stability constants for complexes likely to be formed in a cementitious repository for intermediate and low level nuclear waste. Cellulosic materials in the waste in such repositories are likely to be degraded into potential ligands such as isosaccharinic acid. Thus, there is a need for knowledge of the complexes that they may form with radionuclides in the waste. [Continues.

Laser-Driven Particle Acceleration - Improving Performance Through Smart Target Design

Laser-driven particle acceleration makes use of sub-picosecond, pulsed, high-power laser systems, capable of producing intensities ~10^{19} W/cm^2 at the laser focus to form plasmas, and use ultra-relativistic and nonlinear dynamics to produce quasistatic acceleration fields. This allows electrons to be accelerated to ~100 MeV over sub-centimetre distances, while protons may be accelerated to the ~10 MeV regime. In addition, novel sources of x-ray radiation become available with these schemes. The topics covered in this thesis focus mainly on target normal sheath acceleration of protons in the overdense plasma regime and laser wakefield acceleration of electrons in the underdense regime. An experimental approach leads to novel acceleration concepts and investigations on properties of new target designs. In the overdense plasma regime, hollow microspheres were found to have the potential to enhance the conversion of laser energy into proton energy. The microscopic structure of the material used as target has impact on electron beam filamentation during electron transport through the target bulk. Long-range order was found to result in smoother beams of TNSA-produced protons as compared to amorphous structures. In addition it was demonstrated that short pulse (fs) laser-solid interactions produce magnetic fields, the strength of which can reach 10 kT, mimicking astrophysical conditions. In the underdense regime, it was found that when tailored appropriately, density ramps can provide means of dividing the laser wakefield acceleration process into four steps: nonlinear laser evolution, trapping, bunch transfer into the second bucket, and acceleration, resulting in beams with reduced relative energy spread and divergence compared to self-injection by a nonlinear plasma wave. It was further shown that capillaries can be used to improve efficiency by guiding and refocusing the laser light onto the central axis. Short bursts of soft x-rays were produced inside capillaries. Finally, the use of an asymmetric laser field at the focus facilitated off-axis electron injection into the accelerating phase of a plasma wake oscillation and enhanced x-ray emission