Spark Discharge: Application to Multielement Spectrochemical Analysis

Spark discharge is shown to be a cyclic process of energy dissipation, with one spark in a time-connected train influenced by its relation to predecessor sparks. Spectroscopic instruments having temporal, spatial, and spectral resolution indicate that the light emission is highly ordered with cylindrical symmetry about the current-conducting spark channel. The favored spatial coincidence is between the channel and the most highly ionized and most excited species sampled from the cathode, with less ionized and less excited species emitting farther outward. Light absorption occurs to such an extent that there are full line reversals in excited states of magnesium ions, distant from the channel. Schlieren data indicate a toroidal structure in the postdischarge environment. Charge transfer, Penning ionization, and sensitized fluorescence are thought to be the chemical mechanisms responsible for the spectroscopic topography. Experiments in spectrochemical analysis based on the topography and designed for increased sensitivity, reduced matrix effects, and simpler spectra are discussed.