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Atomic Absorption Spectroscopy (AAS) is a technique that deals with the absorption of electromagnetic radiation of free gaseous atoms at a specific wavelength. AAS allows the measurement of extremely small amounts of elements and is extensively used throughout the world in medicine, manufacturing, mining, environmental monitoring, and laboratories.
Overview of Spectroscopy
Spectroscopy can be traced back to 1648, when Marcus Marci Von Kronland, a Bohemian physicist, discussed optics, color and rainbow in his book titled Thaumantius. Optical spectroscopy was even found in 1672 from Newton’s description of how sunlight splits into different colors when passed through a prism and since then the word ‘spectrum’ came into focus.
In 1802, William Hyde Wollaston analyzed sunlight, which led to the discovery of black lines in the spectrum, however, it was left uncharacterized. Fraunhofer, starting in 1817, began to map and study the dark lines, designating some of the more prominent ones with letters starting with “A” at the red end of the spectrum. These black lines were later explained as a result of the absorption of light in the sun’s atmosphere by Sir David Brewster in 1820.
Atomic Absorption Spectroscopy (AAS)
Robert Bunsen and Gustav Kirchhoff studied the sodium spectrum and concluded that every element has a specific spectrum that can be used to identify elements in their gaseous phase. Kirchoff further explained the phenomenon that if a material emits electromagnetic radiation of a certain wavelength, it may also absorb radiation of that wavelength.
Despite these early discoveries, AAS was mostly limited to astrophysical studies and was virtually ignored until 1950, probably due to the high level of difficulty of the technique and also there was a need for a very high resolution to make quantitative measurements.
In 1952 Alan Walsh, a physicist working in the Chemical Physics Section of the CSIRO Division of Industrial Chemistry in Melbourne, Australia, overcame the lingering problem. This was done with the use of a special type of atomic spectral lamp (usually a hollow-cathode lamp), which emitted a pulsed signal of very narrow spectral lines characteristic of the element being determined, one or more of which could be absorbed by the atoms of this element in the flame.
It was probably due to his experience in two complementary fields of spectroscopy, i.e., in emission spectrochemical analysis and in infrared absorption, that led him to invent the double-pass monochromator. In 1953, CSIRO filed a patent application and in March 1954, an instrument to demonstrate the atomic absorption technique was shown at an exhibition in Melbourne.
Principles of AAS and its Potential for Chemical Analysis
In 1955 Walsh published his classic research paper on the principles of AAS and its potential for chemical analysis. In the same year, two Dutch physicists, Alkemade and Milatz, independently published similar findings on the absorption flame photometer. However, neither the instrument displayed at the exhibition nor Walsh’s paper created much interest except for a few scientists across the world.
In the next few years, Walsh and his team perfected the instrument and promoted its wide-ranging applications. Perkin-Elmer, a leading American company specializing in life science research, was advised by their consultant W.B. Mason (School of Medicine and Dentistry at the University of Rochester) about the long-term benefit of ASS in clinical studies. Walsh demonstrated the usefulness of ASS by applying it in the determination of calcium and magnesium in blood serum. Henceforth, AAS was widely commercialized.
Using AAS in Metal Determination
Licensed sales of ASS rapidly grew throughout the 1960s and beyond, from 6 in 1959 to 750 in 1965 and 2950 in 1970. Even after 60 years of Walsh’s original invention, the determination of metals by AAS, with either flame or furnace atomization, is still widely practiced. It must be noted that clinical laboratories have largely given up flame AAS. However, furnace AAS for heavy metal determinations, particularly in deficiency studies and toxicology, continues to be used.
The market for the Atomic Absorption Spectroscopy instrument is a thriving one and is expected to grow at roughly 6.5% over the next five years, and will reach 680 million US$ in 2024, from 470 million US$ in 2019, according to a new global study.
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