2.1 Introduction and History of AAS
The first observation of atomic emission dates back to at least the first campfire where hominoids/humans observed a yellow color in the flame. This color was caused by the relaxation of the 3p electron to a 3s orbital in sodium (refer to the energy level diagram in Figure 1-3 given earlier), and in part by carbene ions. Slightly more advanced, but still unexplained observations were responsible for the first development of colorful fireworks in China over 2000 years ago. A few of the more relevant discoveries for atomic spectroscopy were the first observations by Newton of the separation of white light into different colors by a prism in 1740, the development of the first spectroscope (a device for studying small concentrations of elements) in 1859 by Kirchhoff and Bunsen, and the first quantitative analysis (of sodium) by flame emission by Champion, Pellet, and Grenier in 1873. The birth of atomic spectrometry began with the first patent of atomic absorption spectrometry by Walsh in 1955. In the same year, flames were employed to atomize and excite atoms of several elements. The first atomic absorption instrument was made commercially available in 1962. Since then, there have been a series of rapid developments that are ongoing in atomic and emission spectrometry including a variety of fuels and oxidants that can be used for the flame, the replacement of prisms with grating monochromators, a variety of novel sample introduction techniques (hydride, graphite furnace, cold vapor, and glow discharge), advances in electronics (especially microprocessors to control the instrument and for the collection and processing of data), and the development of atomic fluorescence spectrometry. Surprisingly, detection limits for the basic instruments used in flame atomic absorption and emission spectrometry have improved little since the 1960s but specialty sample introduction techniques such as hydride generation and graphite furnace have greatly improved detection limits for a few elements.
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