This chapter explains the basic theory of continuous wave (CW) electron paramagnetic resonance (EPR), illustrating the power of the technique to study a wide range of paramagnetic systems. It cites several experiments based on pulsed techniques similar to those routinely employed in nuclear magnetic resonance (NMR) spectroscopy. It also talks about how Pulse EPR can offer significant advantages over CW methods, such as direct detection of relaxation times and access to longer distances between paramagnetic centres. The chapter talks about the independent control of the electron and nuclear spins via the application of short microwave (MW) and radiofrequency (RF) pulses. It presents the vector model and product operator formalism used in pulse techniques.
Chapter
1Advanced EPR techniques
Chapter
Allowing for non-ideality: activity coefficients
Chapter 2 focuses on the concept of activity and explains its relationship to the concentration of ions in solution. The ideality and non-ideality of solutions are discussed and the physical origins of deviations from the former are outlined. The gross non-ideality of electrolyte solutions is emphasised together with the use of Debye-Huckel theory and its extensions in quantifying the relationship between concentration and activity. The solvation of ions in aqueous solution is discussed. Salt effects on the solubility of poorly soluble solids and on the kinetics of homogeneous chemical reactions are explained.
Chapter
The Analyst’s Toolbox
This chapter emphasizes the importance of knowing and appreciating the various strengths and limitations of various techniques used for analysis. It focuses on instrumental methods which stem from endeavours to extend the human senses, describing a fairly large range of instruments and the methods associated with each. It also profiles five important types of techniques and instruments that are applied to the majority of problems or applications in chemistry. The chapter introduces ultraviolet-visible (UV-vis) spectroscopy, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectrometry (NMR), mass spectrometry (MS), and chromatography (liquid chromatography [LC] and gas chromatography [GC]). It explains how spectrometric methods extend one's ability to see molecules and detect molecular interactions that are outside normal human senses, while chromatography deals with the efficient separation of components of a mixture.
Chapter
The analytical approach: defining the problem
This chapter explains the six steps to solving a problem in analytical chemistry and defines a problem in a number of scenarios. It outlines a problem solving strategy that is applicable to a range of problems. It also focuses on defining the problem, wherein analysts consider a series of important questions that are analysed in sequence. The chapter explains how analysts evaluate the conditions required to take a suitable sample in order to help answer the main question posed in the first step, such as questions on what should be measured and why should it be measured. It discusses the techniques and methods analysts use in the measurement process.
Book
E. Hywel Evans and Mike E. Foulkes
Analytical Chemistry starts by defining the analytical approach in terms of a framework for dealing with problems. It then looks at sampling. The chapter that follows is about sample preparation. The text moves on after that to look at instrument measurement techniques. There follows a chapter on calibration and quantitation. The text also considers reference materials and standards. Next, it looks at sampling error. Finally, the book considers method validation and quality assurance.
Chapter
Anisotropic EPR spectra in the solid state
This chapter explores the origins of the anisotropies in g and A for a spin. It explains how symmetry derived anisotropies in the solid state are manifested through g and how the interpretation of this tensor provides valuable information on the symmetry of the paramagnetic centre. It also concentrates on the lineshapes for powder spectra and the origins of the hyperfine A tensor. The chapter considers the electron paramagnetic resonance (EPR) spectra of a paramagnetic vanadyl and presents the theory explaining the origins of anisotropies. It describes a tensor as a mathematical object that illustrates a physical property and outlines the rank of the tensor that depends on the number of directions needed to describe that property.
Chapter
Applications
This chapter offers a short overview of present developments and research in electroanalysis and its applications. It is not possible to describe all types of modern electroanalytical procedures. The chapter then looks at future developments in the area. Applications are particularly important in the areas of industrial, environmental, and clinical analyses. Present general challenges include the miniaturisation of electrochemical sensors, the reduction of their response time, their use on-line, and automation—which includes solving all associated problems such as periodic calibration, electrode fouling, and being sufficiently robust. To illustrate, the chapter provides examples from potentiometric sensors, electrode surface modification, microelectrodes, flow systems, hyphenated techniques, and bioelectroanalysis.
Chapter
Atomic Absorption Spectroscopy
This chapter reviews atomic absorption spectroscopy (AAS), which is an elemental analysis technique used to identify and quantify the elements present in a sample matrix. It states that AAS is fundamentally a form of ultraviolet-visible (UV-vis) absorption spectroscopy that requires the analyte to be first converted to atomic vapour prior to analysis. It also explains how AAS is used to quantify the elemental contents of a sample matrix rather than a tool used to probe the molecular nature of a pure analyte. The chapter highlights the utility of AAS in its capacity for elemental determination within complex matrices such as soil, water, petroleum, plastics, paint, and plant and animal tissue without the need to isolate or purify the analyte from the matrix. The chapter determines a basic block schematic of an AAS that looks similar to a basic block schematic of a UV-vis spectrometer.
Chapter
Atomic Emission Spectroscopy
This chapter compares atomic emission spectroscopy (AES) with luminescence spectroscopy. There are fundamental differences in the techniques which involve vibronic versus purely electronic transitions. The chapter explains that AES is similar to molecular luminescence spectroscopy as the emitted light is measured from excited state analyte. It also considers AES as an atomic method that requires the sample be in the free gas state, necessitating a high-temperature atomizer that is not amenable to physical containment. The chapter points out that AES atomizers are much hotter than atomic absorption spectroscopy (AAS) as the number of atoms in the excited state is an exponential function of temperature. It outlines the atomization step in AES, which both produces atoms and causes their electronic excitation.
Book
T. P. Softley
Atomic Spectra starts off by looking at quantum mechanics and the relationship of quantum mechanics with light. The next chapter considers the structure and spectrum of the hydrogen atoms. The text also covers the spectrum of the helium atom. Finally, the text examines the spectra of many-electron atoms.
Chapter
Basic statistics
This chapter analyses a range of methods to display analytical data and basic statistical concepts. It explains how to use a t-test to compare a mean with a true value. It shows how to make a comparison of two means and how to utilize appropriate statistical tests and graphical methods to evaluate and interpret analytical data in a variety of contexts. It also discusses a way of comparing measurements to support any decisions made by using statistics. It examines studying the data visually. The chapter highlights the use of blob plots for small datasets of up to ten data points on a horizontal scale. It mentions histograms for large datasets, wherein the vertical axis gives the number of results that fall within a small defined range on the horizontal measurement scale.
Chapter
A brief overview of Electron Paramagnetic Resonance spectroscopy
This chapter provides a background on electron paramagnetic resonance (EPR) spectroscopy, which is a magnetic resonance technique used for the study of systems containing unpaired electrons. It explains how EPR systems are paramagnetic and attracted by magnetic fields. It also reviews the applications of EPR in a wide variety of gaseous, liquid, and solid samples and confined to systems bearing unpaired electrons. The chapter outlines basic principles and the underlying physics of EPR. These are similar to those encountered in nuclear magnetic resonance (NMR). It points out how EPR and NMR techniques deal with the interaction of electromagnetic radiation with inherent magnetic moments within the sample.
Chapter
Calibration and quantitation
This chapter details how to prepare a series of working standards to be used for instrument calibration and how to plot a calibration curve and fit a linear trend line. It talks about the of use a calibration curve to calculate the analyte concentration in a sample and distinguishes the different sources of errors that can occur in instrumental analysis. It also explores the actuality of making an analytical measurement and analyses qualitative analysis which is normally referred to as selectivity and considered as a necessary pre-condition. The chapter focuses on qualitative analysis concerned with the identification of an analyte rather than the measurement of its quantity, such as mass spectrometry. This can be used to identify controlled drugs in body fluids for forensic purposes. It illustrates the mass spectrum of morphine, which comprised of fragments of the molecule that have different masses.
Chapter
Chemical exchange
P.J Hore
This chapter evaluates the theory of chemical exchange, which is straightforward compared to the complex computations required to obtain chemical shifts and J-couplings. Chemical exchange effects in nuclear magnetic resonance (NMR) arise from dynamic chemical and conformational equilibria. The chapter studies the cases of symmetrical two-site exchange and unsymmetrical two-site exchange. NMR lines are broadened by slow exchange. Meanwhile, differences in the NMR frequencies of exchanging spins (δν) can be averaged by fast exchange. The magnitude of δν relative to the exchange rate constant(s) determines whether the exchange is 'slow' or 'fast'. Ultimately, chemical exchange effects give information on the rates and mechanisms of chemical reactions, molecular rearrangements, and internal motions.
Book
Richard R Wayne
Chemical Instrumentation introduces chemists to some of the building blocks and devices that make up the most important instruments used in industry and research. Instrumentation, often of a highly sophisticated kind, lies behind many of the most interesting aspects of contemporary chemistry. Some techniques—such as NMR—owe their existence to electronic instrumentation; others have been made simpler, more reliable, and more precise. Yet undergraduates reading chemistry often have only the most rudimentary understanding to be performed. Simple measuring devices are discussed before the introduction of the constituent elements of more complex devices, and emphasis is given to the enhancement of signal-to-noise ratios, which often lies at the heart of some of the most demanding measurements in the chemical sciences.
Chapter
Chemical shifts
P.J Hore
This chapter discusses chemical shifts. These give information on molecular identity and structure. The nuclear magnetic resonance (NMR) frequency of a nucleus in a molecule is determined principally by its magnetogyric ratio and the strength of the magnetic field it experiences. Chemical shifts arise because the field actually experienced by a nucleus in an atom or molecule differs slightly from the external field produced by the magnet. A magnetic field can induce two kinds of electronic current in a molecule: diamagnetic and paramagnetic. Diamagnetic and paramagnetic currents flow in opposite directions and give rise to nuclear shielding and deshielding, respectively. Chemical shifts can often be understood by considering the effects of electron donating and withdrawing groups, induced currents in neighbouring groups, charged or polar groups, hydrogen bonds, and unpaired electrons.
Chapter
Computers in instrumentation
This chapter examines some basic concepts of computer techniques which are now widely used in instrumentation. It covers digital integrated circuits that are wired together in an approximate way. These can provide sequences of logical operations of great complexity. It also points out that the computer consists of the hardware, which are logic circuits wired together to provide a small number of sophisticated operations, and the software, which covers the order and repetition of the operations under the control of a program. The chapter recounts the breakthrough in the use of computing techniques that came with the development of microprocessors. It reviews the size and cost of the integrated circuit microprocessors, which make their incorporation into relatively simple instrumentation a feasible proposition.
Chapter
Density matrices
Introduction
The introduction of operator exponentials provides a huge simplification in describing the evolution of NMR spin states, but the solution is still given as a vector of coefficients, which has to be further interpreted to obtain information about the observable NMR signal. In this...
Chapter
Dynamic NMR spectroscopy
This chapter focuses on dynamic NMR spectroscopy. Intra- and intermolecular dynamic processes affect the appearance of NMR spectra. When the dynamic process is slow, separate resonances are observed for each site. When the process is fast, a resonance at the weighted average chemical shift is seen. Exchange not only affects the chemical shift but also the couplings seen. If the dynamic process is intermolecular exchange, decoupling is observed due to the breaking of the bonds between the exchanging groups. If the process is intramolecular a weighted average coupling constant is seen to all the neighbouring spins involved. Dynamic processes can be studied by both variable temperature spectroscopy and by EXSY NMR, allowing the intimate mechanism of the dynamic process to be determined.
Book
Christopher M. A. Brett and Ana Maria Oliveira Brett
Electroanalysis introduces the techniques and areas of application of modern electroanalysis, which has a particularly important role within current environmental concerns, both in the laboratory and in the field. The text begins by describing the basic principles of the necessary electrochemistry and then moves on to electrochemical sensors and their mode of functioning. Potentiometric sensors are described, including many types of selective electrode. Following this, amperometric and voltametric sensors are discussed together with the various instrumentation and electrode modification strategies to enhance sensitivity and selectivity. A final chapter shows the range of applications of modern electroanalysis, with particular emphasis on trace species, and indicates future trends.
