Preliminary characterization and fundamental properties of aerosols generated by a flow focusing pneumatic nebulizer

Abstract

A new pneumatic concentric nebulizer (flow focusing pneumatic nebulizer, FFPN), based on the capillary flow focusing effect which produces highly controllable fine aerosols, is presented for the first time for analytical applications. The key aerosol diagnostic data and analytical figures of merit obtained using ICP-AES are presented for the FFPN and compared with a commercially available glass concentric nebulizer (conical nebulizer, CK). To perform a fair comparison, both nebulizers have been run under their own standard working conditions. Under all the conditions studied, the FFPN produces a finer primary aerosol than the conventional pneumatic nebulizer. At a solution uptake rate of 2.0 mL min⁻¹ and a nebulizer gas flow rate of 1.0 L min⁻¹ for the CK, and at a solution uptake rate of 0.2 mL min⁻¹ and a nebulizer gas flow rate of 0.7 L min⁻¹ for the FFPN, the median diameter (D₅₀) values of the primary aerosol are 24.64 μm and 3.82 μm with the CK and FFPN, respectively. The tertiary aerosols of the CK and FFPN studied do not show a substantial difference, the D₅₀ values, under the same operating conditions stated above, being 2.89 μm and 2.87 μm for the CK and FFPN, respectively. Under most of the studied conditions, all the primary aerosols produced by FFPN are contained on droplets smaller than 10 μm. For example, under the above experimental conditions, nearly 22% and 98% of primary aerosol volume is contained on droplets having sizes less than 10 μm for the CK and FFPN, respectively. However, approximately all the tertiary aerosol volume is contained on droplets smaller than this diameter with both nebulizers. This is the result of strong filtering action of the cyclonic spray chamber used, with a cut-off diameter of 15 μm, when CK is used. In general, sensitivities, precision and limits of detection with the FFPN are similar or better than those of the CK, yet with a sample uptake rate of only one-tenth the CK rate.