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 a nd vaporizing particles were investigated. Time-gated laser-excited fl uorescence 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 measureme nts 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. Em ission measurements gated to the presence and absence of droplets and particles are also reported. Large decreases in the extent of excitati on 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 th ermodynamic equilibrium model. Calculated electron number densities ba sed upon fluorescence ratios were more than an order of magnitude lowe r near either droplets or particles. Based upon emission to fluorescen ce ratios, electron number densities changed by roughly one order of m agnitude.