THE EFFECT OF DESOLVATING DROPLETS AND VAPORIZING PARTICLES ON IONIZATION AND EXCITATION IN AR INDUCTIVELY-COUPLED PLASMAS

Plasma conditions near and far from incompletely desolvated droplets and vaporizing particles were investigated. Time-gated laser-excited fluorescence measurements show that Sr atom number densities increase by more than a factor of 40 near incompletely desolvated droplets and by more than a factor of 60 near vaporizing particles. Similar measurements show a 2.6-fold increase in Sr ion number densities near droplets and a seven-fold increase near vaporizing particles. Decreases in the extent of analyte ionization near droplets and particles are noted. Emission measurements gated to the presence and absence of droplets and particles are also reported. Large decreases in the extent of excitation near droplets and particles are indicated by changes in emission to fluorescence ratios. Temperatures and electron number densities were roughly estimated based upon ion to atom fluorescence and emission to fluorescence ratios using the Burton-Blades correction to the local thermodynamic equilibrium model. Calculated electron number densities based upon fluorescence ratios were more than an order of magnitude lower near either droplets or particles. Based upon emission to fluorescence ratios, electron number densities changed by roughly one order of magnitude.