Discussion of Instruments

Within the confines of the present volume it is not possible to provide a detailed discussion of instrumentation for atomic fluorescence spectroscopy. An instrument for simultaneous multi-element determination described by Mitchell and Johansson53 has been developed commercially. Many atomic absorption spectrophotometers can be adapted for fluorescence measurements and details are available from the manufacturers. Detailed descriptions of atomic fluorescence spectroscopy are to be found in many of the volumes listed in the Bibliography (Section 21.27). 

Because the end point (formation of a permanent brownish coloration) is not very sharp, the back titration method (Ref 4) was used successfully by Dr Fedoroff at the Keystone Ordn Works, Meadville, Pa and improved at PicArsn (Ref 9a). More recently, an electrometric method for detection of the end point was proposed (Refs 5, 6, 7, 8 and 11 Refs 6 7 are discussions of instrumental design and not primarily about FeS04 to detn nitrate). 

For an alternate discussion of instrumental techniques see J. W. Cooper, Spectroscopic Techniques for Organic Chemists, Wiley Interscience, New York, 1980. 

The fundamentals of instrument design on an elementary level are discussed by Carlson (3). Discussions of instrumentation from a point of view of manufacturers specifications is presented in two older articles (20, 21). Among the manufacturers listed in Evans article (21), Hewlett-Packard and E.I. duPont no longer manufacture instruments. It is advisable to consult current manufacturers for up to date specifications of instrumentation. Development of instrumentation has not kept pace with recent activity in the field and hopefully instrument manufacturers currently manufacturing instruments will devote more effort to development in the future. 

Most isotope ratio measurements have been performed using sector mass spectrometers. Some work has been reported, notably by Heumann [35], in which a quadrupole-based system was used. Instruments used for measurement of isotope ratios are most often dedicated to that purpose. In most instances only a relatively small mass range needs to be monitored, just enough to encompass the isotopes of the analyte element. Without the ability to scan the entire elemental mass range [usually from mlz = 6 (Li) through mfc = 238 (U) for elemental analysis], mass spectrometers designed to measure isotope ratios cannot readily be adapted for other purposes. See Chapter 2 for a discussion of instrumentation required for elemental analysis of solid materials and Chapter 3 for a treatment of the in-strumenation needed for elemental analysis of solutions. 

No ordinary monochromator is capable of yielding a band of radiation as naiTOW as the width of an atomic absorption line (0.002 to 0.005 nm). As a result, the use of radiation that has been isolated from a continuum source by a monochromator inevitably causes instrumental departures from Beer s law (see the discussion of instrument deviations from Beer s law in Section 24C-3). In addition, since the fraction of radiation absorbed from such a beam is small, the detector receives a signal that is less attenuated (that is, P —> Pq) nd the sensitivity of the measurement is reduced. This effect is illustrated by the lower curve in Figure 24-17 (page 733). 

See Bruno Latour s discussion of instruments as inscription devices (Latour, 1987, chap. 2). 

This chapter was written to provide abrief discussion of instrumentation, present the advantages and disadvantages of specimen preparation techniques for biochemical research, assess the sources of error and artifact, provide selected examples of applications, and outline general experimental procedures, where they can be prescribed appropriately. 

More detailed descriptions of the instrumentation and theory of ESR may be found in several books [1, 6-11]. As an introduction, the book by Symons [8] is particularly useful and for a detailed discussion of instrumentation the work by Poole [11] can be recommended. 

The accuracy and precision of spectrophotometric analyses arc often limited by the uncertainties or noise associated with the instrument. A general discussion of instrumental noise and signal-to-noise optimLaiion is found in Chapter 5. 

The individual authors were asked to make the theoretical background of each method as brief and qualitative as possible consistent with clarity and accuracy, to limit discussion of instrumentation to general principles as far as possible (i.e., no details of the operation of commercially available apparatus), and to emphasize the utility and actual applications of each method. 

Timothy Mouw, Sphere versus 0/45, A Discussion of Instrument geometries and Their Areas of Application, X-Rite,... 

In our discussion of instrumentation foctors, we will stress their effects on excitation and emission spectra. However, similar concerns are inqx>rtant in the measurement of fluorescence lifetimes and anisotropies, which will be described in Chapters 4, 5, and 10. Additionally, the optical prc rties of the samples, such as optical density and turbidity, can also affect the spectra. Specific examples are given to clarify these effects and the means to avoid them. 

While a detailed discussion of instrumental methods is well beyond the scope of this book (the interested reader should consult the further reading list at the end of this chapter), it is appropriate to acknowledge their contribution to electrochemical technology. They are largely responsible for the detailed information which is available about the electrode reactions used in commercial processes. 

Materials such as tantalum, too expensive for widespread use in larger items, are common in instruments. The discussion of instrument materials of construction in this book is in Chapter 11, and Sections 11.5 and 11.6 in particular discuss applications in caustic service. 

This chapter is devoted to a discussion of instruments and techniques that are of fundamental importance for the measurements of wavelengths and line profiles, or for the sensitive detection of radiation. The optimum selection of proper equipment or the application of a new technique is often decisive for the success of an experimental investigation. Since the development of spectroscopic instrumentation has shown great progress in recent years, it is most important for any spectroscopist to be informed about the state-of-the-art regarding sensitivity, spectral resolving power, and signal-to-noise ratios attainable with modern equipment. 

Sample preparation and measurement procedures are very important, especially for infrared methods of analysis. A brief discussion of instrumentation and sample handling accessories, along with a summary of the most common sample handling methods, is provided in Sec. 5. Raman spectroscopy is quite diflerent from infrared spectroscopy, insofar as there is... 

A short description of FT-IR spectrometers is included in the discussion of instrumentation on the website (Chapter 8W, IR section. Part IV). 

From simple solvent extraction to RIA, sample preparation and screening tests share many common elements. The pivotal characteristics are (1) the existence of a difference in properties between the materials to be separated and (2) an exploitable equilibrium. An understanding of these ideas facilitates an understanding of partitioning and competitive equilibria. All of the sample preparation uid screening procedures and protocols described in this chapter can be characterized by invoking some combination of these foimdational principles. Furthermore, the theory behind TLC and immunoassay forms a bridge that leads naturally into a discussion of instrumentation, the subject of the next chapter. 

This book was written primarily for the new man in infrared spectroscopy, the student and the inexperienced worker, but should also be useful to the more experienced, especially to those whose experience has been limited to one small segment of the field. To cover infrared technology in a comprehensive or detailed manner would require a book of unmanageable size so, except for the chapters dealing with interpretation of spectra, the material covered was limited to broad, general descriptions or discussions of instrumentation, accessories. 

Handbook of Industrial Infrared Analysis, R. G. White, Plenum Press, New York (1964). A discussion of instrumentation and sample handling, plus spectrogram interpretation. 

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