Instrumentation concepts common techniques

Physical Organic Chemistry can be defined as the application of the concepts and techniques of physical chemistry to the study of organic compounds and their reactions. The incorporation of modern instrumental and computational techniques into the discipline has been impressively rapid, but the absorption of new theoretical concepts has been slower. Thus, the criteria of orbital symmetry conservation, that had such a profound influence on mechanistic thinking immediately after its introduction into organic chemistry, are commonly applied today in much the same manner as they were a quarter of a century ago. 

The CEM Discover platform, introduced in 2001, offers a single-mode instrument based on the self-tuning circular waveguide technique (see Fig. 3.3). This concept allows for derivatization of the reactor to accommodate additional application-specific modules to address other common laboratory objectives. While the Discover ... 

PTR-MS combines the concept of Cl with the swarm technique of the flow tube and flow-drift-tube mentioned above. In a PTR-MS instrument, we apply a Cl system which is based on proton-transfer reactions, and preferentially use HsO" " as the primary reactant ion. As discussed earlier, HsO" " is a most suitable primary reactant ion when air samples containing a wide variety of trace gases or VOCs are to be analyzed. HsO" " ions do not react with any of the natural components of air, as these have proton affinities lower than that of H2O molecules this is illustrated in Table 1. This table also shows that common VOCs containing a polar functional group or unsaturated bonds (e.g. alkenes, arenes) have proton affinities larger than that of H2O and therefore proton transfer occurs between H30" and any of these compounds (see Equation 4). The measured thermal rate constants for proton transfer to VOCs are nearly identical to calculated thermal, collisional limiting values (Table 1), illustrating that proton transfer occurs on every collision. 

The basic concepts of atomic absorption spectrometry were published first by Walsh in 1955, this can be regarded as the actual birth year of the technique. At the same time Alkemade and Milatz designed an atomic absorption spectrometer in which flames were employed both as a radiation source and an atomizer. The commercial manufacture of atomic absorption instruments, however, did not start until ten years later. Since then the development of atomic absorption spectrometry has been very fast, and atomic absorption (AA) instruments very quickly became common. The inventions of dinitrogen oxide as oxidant and electrothermal atomization methods have both significantly expanded the utilization field of atomic absorption spectrometry. These techniques increased the number of measurable elements and lowered detection limits. Todays graphite furnace technique is based on the studies of King at the beginning of the twentieth century. 

As discussed in more detail in Sect. 1.1.5, this volume of the Encyclopedia is divided into three broad sections. The first section, of which this chapter is an element, is concerned with introducing some of the basic concepts of electroanalytical chemistry, instrumentation - particularly electronic circuits for control and measurements with electrochemical cells - and an overview of numerical methods. Computational techniques are of considerable importance in treating electrochemical systems quantitatively, so that experimental data can be analyzed appropriately under realistic conditions [8]. Although analytical solutions are available for many common electrochemical techniques and processes, extensions to more complex chemical systems and experimental configurations requires the availability of computational methods to treat coupled reaction-mass transport problems. 

---