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Determination of the concentration of atoms in a gas by atomic absorption spectroscopy

Determination of the concentration of atoms in a gas by atomic absorption spectroscopy

The discovery and history of atomic absorption studies are inextricably linked with the entire history of spectroscopy and spectral analysis. In 1802, Wollaston, reproducing Newton's experiment on the expansion of the continuous solar spectrum, first discovered that if a beam of sunlight is passed not through a round hole in the shutter, but through a slit, then the solar spectrum is intersected by several dark lines. However, this discovery did not attract attention. Fifteen years later, independently of Wollaston, Fraunhofer again discovered dark lines in the spectrum of the Sun, which received the name Fraunhofer in his honor.

The origin of the dark lines was established only in 1859 by Kirchhoff. Kirchhoff was the first to make a clear conclusion about the possibility of determining the chemical composition of a substance from the spectra. In joint work with Bunsen, Kirchhoff gave numerous examples of the use of spectra for the determination of alkali metals in a flame. Therefore, Bunsen and Kirchhoff are rightly considered the founders of spectral analysis.

In 1861, Kirchhoff published a work on the spectral analysis of the chemical composition of the solar atmosphere, in which he, by the coincidence of the emission lines of certain elements with the Fraunhofer lines of the solar spectrum, stated the presence of these elements on the Sun. As a result, astrophysics and astrochemistry are becoming the most important areas of application of atomic absorption spectroscopy, which determine the chemical composition, physical state and nature of the motion of celestial bodies.

The first two decades of the XX century. are marked by significant achievements in the field of the theory of atomic absorption. During this period, the main relations were established: connecting the absorption value with atomic constants, a theory of line broadening with pressure was formulated, a relation was derived for the absorption line contour under the total action of several broadening effects, and methods for measuring atomic absorption were developed.

Thanks to the theoretical substantiation of absorption processes, it was possible to obtain quantitative data on the solar and stellar atmospheres, their chemical composition, temperatures, electron concentrations, etc. The absorption method has found application in the interpretation of complex spectra, since absorption lines contain lines starting only from low energy levels.

For astrophysical purposes, plasma studies, clarification of the structural features of the atom, it is important to know the lifetimes of excited states of atoms and the effective cross sections of atoms in collisions with foreign gas molecules. Absorption measurements are also used in the study of the hyperfine structure of atomic lines and the Zeeman effect, that is, in those cases when very narrow spectral lines are needed to register the phenomenon.

The use of atomic absorption in analytical chemistry begins in the forties and concerns exclusively the determination of mercury vapor in the air. In 1954, a work by OP Bochkova appeared on the use of atomic absorption for the analysis of gases. These isolated works limited the analytical use of atomic absorption spectroscopy up to 1955. In 1955, Walsh revealed the most significant advantages of absorption methods over emission ones, proposed a rational method for recording atomic absorption, and recommended a setup scheme for carrying out analyzes.

Work on atomic absorption spectroscopy is carried out not only in the field of its application for the analysis of the elementary composition of matter, but also in other areas: absorption methods for analyzing gases, simplified methods for determining the isotopic composition of elements are being developed, measurements of the absolute values of the oscillator forces and the resonance width are carried out. Lines, diffusion coefficients of vapors of elements in inert gases.



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