A nebulizer design for inductively coupled plasma spectrometry

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Inductively coupled plasma optical emission spectroscopy (ICP-OES) and mass spectrometry (ICP-MS) can be considered as the most important tools in inorganic analytical chemistry. In these system, a liquid sample is atomized into small droplets and introduced into a plasma. For a proper operation, the droplet sizes should be small, preferably less than 5 microns. Most commercially available systems use pneumatic nebulizers, which generate a broad range of droplet size distributions, mainly in the range of 1-100 microns. Therefore, a spray chambers is added downstream of the nebulizer to remove large droplets. This, however, results that only a small fraction (less than 5%) of the nebulized sample actually contributes to the measured signal. For very small sample sizes, micro-nebulizers are used, which have very small size orifices to generate small droplets for small sample uptakes. However, these systems are prone to blockage and clogging, in particular for high viscosity solutions and solutions containing total dissolved solid, making them basically impractical. Despite a significant amount of research and the high number of publications devoted to liquid sample introduction, this problem still persists to be what limits the efficiency of atomic spectrometry.We are proposing a novel method for the nebulization of liquid samples, which we believe would significantly improve the efficiency of ICP systems. The proposed method is based on using an ultrasound nebulizer in combination with a controlled gas mixing system to limit the droplet collision and coalescence. Ultrasound nebulizers can be designed to generate very small droplets (~ 5micorns). However, the droplet sizes at certain frequencies also depends on the liquid properties. One objective of the present research is to determine this dependency for a wide range of practical fluid properties, and determine the ultrasound frequency and amplitude needed to keep the droplet sizes small for a relatively higher viscosities (up to 100 cP). Another objective of the present research is to develop a mixing chamber to rapidly disperse the high density aerosol that is generated by the ultrasound nebulizer in order to prevent secondary collision and coalescence, which may result in an increase in droplet sizes.