Ionization in flames

Possible applications of laser enhanced ionization in flame diagnostics are 1. simultaneous observation of ionization and fluorescence signals from various levels might provide more information on the sequence of processes leading to and from the ionization continuum 2. the measurement of ion mobilities, relating to cross-sections for elastic collisions between ions and flame particles 3. measurement of ionization rate constants relating to cross-sections for inelastic collisions between excited atoms and other flame particles 4. measurement of recombination rate constants, relating to cross-sections for inelastic collisions between ions, electrons and neutrals. 

The alkali metals Li, Na, and K are easily ionized in flames and plasmas. Concentrations of an easUy ionized element (EE) greater than 1000 ppm in solution can result in suppression or enhancement of the signals from other analytes. The EE effect is wavelength dependent ion lines are affected differently than atom lines. The EE effect can be minimized by optimizing the RF power and plasma conditions, by matrix-matching, by choosing a different wavelength that is not subject to the EE effect, or by application of mathematical correction factors. 

The study of ionization in flames demands an analytical technique for the determination of the concentration of ions. There are many difficulties, both experimental and in interpretation, associated with the measurement of the d.c. conductivity of a flame and some specificity in analysis is desirable. 

Bolton, H.C. Grant, J. McWilliam, I.G. Nicholson, A.J.C. Swingler, D.L., Ionization in flames. II. Mass-spectrometric and mobility analyses for the flame ionization detector,... 

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