VERTICAL AND RADIAL EMISSION PROFILES AND ION-ATOM INTENSITY RATIOS IN INDUCTIVELY COUPLED PLASMAS - THE CONNECTION TO VAPORIZING DROPLETS

Vertical Ca I and Ca II emission intensity profiles appear to be directly related to the number of incompletely desolvated droplets at each height in the plasma. The number of desolvated aerosol droplets at the height of peak time-integrated Ca I 422 nm emission intensity is constant (about 10.5 thousand counts/s) regardless of where the peak occurs as the power and center (nebulizer) gas flow rate are varied. Similarly, the number of incompletely desolvated droplets near the height of peak time-integrated Ca II emission intensity is constant (about 550 counts/s) even when the power and center gas flow rate are changed, resulting in variations in the location of the maximum Ca II 393 nm emission intensity. Therefore, incompletely desolvated aerosol droplets appear to be a key variable controlling vertical emission profiles. Radial Ca I and Ca II emission intensity profiles are different in the presence and absence of a nearby incompletely desolvated droplet. Time-resolved Ca II to Ca I emission intensity ratios acquired from a fixed height in the plasma vary by up to a factor of 70. Between the height of maximum time-integrated Ca I emission intensity and maximum time-integrated Ca II emission intensity the time-integrated ion to atom emission intensity ratio is controlled by the fraction of time an incompletely desolvated droplet is near the observation zone.