CHAPTER 8 - MICROWAVE DISCHARGE AND AFTERGLOW EXCITED EMISSION SPECTRA FOR SPECIFIC DETECTION IN GAS CHROMATOGRAPHY

Abstract

This chapter discusses the application of microwave discharge and afterglow excited emission spectra for specific detection in gas chromatography. In the microwave system, energy from an electromagnetic field can be supplied to a gas by collisions between charged particles, accelerated by the field and neutral species. Of the charged particles, electrons are most effective for the energy transport from the field to the gas. The types of collisions can be classified as—elastic, inelastic, and super-elastic. In elastic collisions the electrons are scattered without exchange of kinetic energy of the electrons to internal energy of the atoms. When an inelastic collision takes place, there is a certain change in the internal state of the atom; here the collision results in an excited or ionized atom. Excited atoms decay fast to a lower state or to the ground state, emitting the excess energy as radiation. When excitation has taken place to a meta-stable state, radiative de-excitation is forbidden and the atoms remain for a considerable time in the excited state. In the chapter, a schematic experimental setup for microwave discharge excitation is illustrated. The chapter shows a chromatogram obtained during the elution of a mixture of n-heptane, chloroform, and carbon tetrachloride.