4 - Spray Chamber Design

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This chapter discusses the designing of the spray chambers of pneumatic nebulizers. Aerosols pneumatically generated have characteristics that prevent their direct introduction into the plasma. Therefore, it is necessary to use an additional component to adapt the aerosol properties to the plasma requirements. The nebulizer is fitted to a spray chamber. Although in some instances (e.g., hydride generation ICP determinations) a spray chamber is used as a gas–liquid separation system, its main function is to remove coarse droplets from primary aerosol. The majority of the useful droplets generated by the nebulizer are lost in this second component of a typical liquid sample introduction system. The mass of solution lost in the spray chamber and the signal are functions of the quality of primary aerosol in terms of fineness, velocity, and shape, which are given by the ability of a nebulizer to produce fine droplets as well as by the nebulization conditions. Nevertheless, it is considered that the spray chamber rather than the nebulizer determines the mass and characteristics of the aerosol introduced into the plasma. The main aerosol transport phenomena occurring inside a spray chamber used for ICP techniques are evaporation, coagulation or coalescence, and impacts caused by droplet inertia, gravitational settling, and turbulences. Double-pass spray chambers, cyclonic type spray chambers, and single-pass spray chambers are the main designs discussed in this chapter. The donut-shaped spray chamber provides higher sensitivities, lower limits of detection, better precision, and lower background levels than a double-pass spray chamber. A simplified, low inner volume spray chamber is designed for use in conjunction with micronebulizers. Solvent evaporation becomes a major phenomenon, and drain may be reduced or even suppressed.