Atomic Emission Spectroscopy—It Lasts and Lasts and Lasts

Atomic emission spectroscopy, probably the first of the spectrometric methods to be used for elemental analysis, is still among the most popular. Paradoxically, however, this most durable technique is also the one that has undergone the most change. The earliest procedures ordinarily employed chemical flames as atomization and excitation devices. Then, in the 1940s and 1950s it was found that electrical discharges such as the dc arc and high-voltage spark offer greater sensitivity and applicability to a broader range of sample types. Glow-discharge devices became available shortly thereafter and were shown to offer higher precision, albeit at the cost of lower sample throughput. In the 1960s and 1970s, the inductively coupled plasma was heralded as the newest and most powerful emission source devised to that date. Along the way, workers also explored the utility of microwave plasmas, electrically heated furnaces, flowing afterglows, and combinations of sources. Amazingly, most of these devices are still in common use. Flame emission spectroscopy is the technique of choice for determining alkali metals in many clinical samples, and the high-voltage spark is the mainstay for quantitation in the metals industry. Direct-current arc spectroscopy is routinely utilized for the characterization of recycled alloys, the inductively coupled plasma is used in laboratories throughout the world for solution samples, and the microwave plasma finds use as a chromatographic detector. At the same time these sources were being developed, explored, and adopted, alternative optical systems, detectors and detector arrays, and signal-processing approaches were being studied for use in emission spectroscopy. In this paper, these developments are outlined and used as a backdrop against which recent advances can be described.