COMPUTERIZED SIMULATION OF MIXED-SOLUTE-PARTICLE VAPORIZATION IN AN INDUCTIVELY-COUPLED PLASMA

The mechanism of matrix interference in ICP spectrometry has been prob ed by incorporation of the droplet-desolvation and solute-particle vap orization processes in a computer simulation of the ICP. Two types of simulation have been carried out: single-aerosol droplet studies, and many-droplet studies. The first type of calculation is used to examine the response of the vaporization kinetics to changes in plasma proper ties (central channel flow rate and forward power) and to aerosol prop erties (initial droplet diameter, concentration of interferent, and th ermal and physical properties of the interferent). From these studies, the dominant mechanism for solute-particle vaporization in the ICP is small-particle mass transfer. In addition, the height in the plasma a t which a solute-particle has completely vaporized is related roughly linearly to the initial diameter of the aerosol droplet, linearly to t he central channel flow rate, inversely to the forward power, and to t he square root of interferent concentration. The second type of calcul ation is a many-droplet simulation for direct comparison with experime ntal results. Ground state atom and ion number densities have been cal culated by simulation of plasma properties, aerosol desolvation and va porization, and flow and diffusion of the analyte vapor. These studies indicate that if early vaporization and lateral diffusion are dominan t reasons for the interelement interference las experiments have sugge sted) then one (or both) of two things must also be true. First, the l imiting mechanism of vaporization predicted by theory may be incorrect , since the small-particle mass-transfer rate constants for all interf erents are lower than or equal to that for CaCl2, the analyte. Also, l iberation of the EIE below the load coil may raise the gas temperature along the central channel, consistent with experimental results; this rise causes an increase in the rate of desolvation and possibly vapor ization. (C) 1998 Elsevier Science B.V. All rights reserved.