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The
valence electrons associated with the free atoms in the hot sample
gases are those involved in both atomic emission and atomic
absorption. They are also those that are situated in the outermost
orbitals of the electron cloud round the nucleus and are those most
easily excited by external radiation or thermal energy. The process
of atomic emission is depicted in figure 1.
The valency electron of the element in its ground state (the lowest energy orbit for that electron) receives thermal energy by collisions with hot gas molecules and is elevated to an excited state. This situation is temporary and the electron falls back to the ground state and at the same time emits a photon of light that has energy equal to the difference between the excited state and the ground state. In fact, in the process, thermal energy has been transformed to the equivalent in radiation energy.
Thus, Ec = hνo (1)
where (Ec) is the energy of excitation,
(h) is Planks constant,
and (νo) frequency of the emitted radiation.
The total intensity of the emitted radiation will be proportional to the number of atoms emitting energy, which, in turn, will be proportional to the concentration of the element in the sample being fed into the emission zone.
That is, Ic = Kc (2)
where (K) is a constant,
and (c) is the concentration of the element in the sample.
Thus, the amount of the element in the sample can be determined by measuring the intensity of the radiation at frequency (νo) emitted from the emission zone.
About the Author
RAYMOND PETER WILLIAM SCOTT was born on June 20 1924 in Erith, Kent, UK. He studied at the
University of London, obtaining his B.Sc. degree in 1946 and his D.Sc. degree in 1960.
After spending more than a decade at Benzole Producers, Ltd. Where he became head of
the Physical Chemistry Laboratory, he moved to Unilever Research Laboratories as
Manager of their Physical Chemistry department. In 1969 he became Director of Physical
Chemistry at Hoffmann-La Roche, Nutley, NJ, U.S.A. and subsequently accepted the position
of Director of the Applied Research Department at the Perkin-Elmer Corporation, Norwalk, CT, U.S.A.
In 1986 he became an independent consultant and was appointed Visiting Professor at Georgetown
University, Washington, DC, U.S.A. and at Berkbeck College of the University of London; in 1986
he retired but continues to write technical books dealing with various aspects of physical chemistry
and physical chemical techniques. Dr. Scott has authored or co-authored over 200 peer reviewed
scientific papers and authored, co-authored or edited over thirty books on various aspects of
physical and analytical chemistry. Dr. Scott was a founding member of the British chromatography
Society and received the American Chemical society Award in chromatography (1977), the
M. S. Tswett chromatography Medal (1978), the Tswett chromatography Medal U.S.S.R., (1979),
the A. J. P. Martin chromatography Award (1982) and the Royal Society of Chemistry Award in
Analysis and Instrumentation (1988).
Dr. Scott’s activities in gas chromatography started at the inception of the technique,
inventing the Heat of Combustion Detector (the precursor of the Flame Ionization Detector),
pioneered work on high sensitivity detectors, high efficiency columns and presented fundamental
treatments of the relationship between the theory and practice of the technique.
He established the viability of the moving bed continuous preparative gas chromatography,
examined both theoretically and experimentally those factors that controlled dispersion
in packed beds and helped establish the gas chromatograph as a process monitoring instrument.
Dr. Scott took and active part in the renaissance of liquid chromatography,
was involved in the development of high performance liquid chromatography and invented
the wire transport detector. He invented the liquid chromatography mass spectrometry
transport interface, introduced micro-bore liquid chromatography columns and used them
to provide columns of 750,000 theoretical plates and liquid chromatography separations
in less than a second.
Dr. Scott has always been a “hands-on” scientist with a remarkable record of accomplishments in chromatography ranging from hardware design to the development of fundamental theory. He has never shied away from questioning “conventional wisdom” and his original approach to problems has often produced significant breakthroughs.