Flow focusing pneumatic nebulizer in comparison with several micronebulizers in inductively coupled plasma atomic emission spectrometry

Abstract

A new pneumatic concentric nebulizer (flow focusing pneumatic nebulizer, FFPN) is characterized and compared with five commercially available pneumatic micronebulizers (high efficiency nebulizer (HEN), PFA-micronebulizer (PFA), MicroMist (MM), Ari Mist (AM) and Mira Mist (MiM)) operated in conjunction with the same cyclonic spray chamber. Primary and tertiary aerosols, transport magnitudes (solvent and analyte transport rates) and analytical figures of merit obtained using inductively coupled plasma atomic emission spectroscopy are measured. Under all the conditions studied, all the primary aerosols produced by FFPN are contained in droplets smaller than 15 μm. Primary and tertiary aerosols produced by FFPN show very similar characteristics. This is the result of the small filtering action of the cyclonic spray chamber used when the FFPN is used. Under all the conditions studied, the FFPN produces a finer and narrower primary aerosol than the commercial pneumatic micronebulizers. At a solution uptake rate of 0.2 mL min⁻¹ and a nebulizing gas flow rate of 0.7 L min⁻¹ the median diameter (D₅₀) values of the primary aerosols are 21.71 μm, 31.75 μm, 16.84 μm, 13.13 μm, 4.92 μm and 3.25 μm with the PFA, MM, AM, MiM, HEN and FFPN, respectively. The tertiary aerosols do not show a substantial difference, the D₅₀ values, under the same operating conditions stated above, being 3.90 μm, 3.91 μm, 4.38 μm, 4.07 μm, 2.95 μm and 3.59 μm for the PFA, MM, AM, MiM, HEN and FFPN, respectively. For example, under the above experimental conditions, nearly 30%, 20%, 44%, 51%, 100% and 100% of primary aerosol volume is contained in droplets having sizes smaller than the cut-off diameter of the spray chamber used (20 μm) for the PFA, MM, AM, MiM, HEN and FFPN, respectively. However, the tertiary aerosol volume contained on droplets smaller than 9 μm ranges between 85%–99%. This is a clear consequence of the strong filtering action of the spray chamber when used with the PFA, MM, AM and MiM nebulizers. Solvent and analyte transport rate values obtained with the FFPN are the highest, the analyte transport rate values being 6.4 μg min⁻¹, 7.0 μg min⁻¹, 5.1 μg min⁻¹, 5.9 μg min⁻¹, 10.1 μg min⁻¹ and 15.8 μg min⁻¹ for the PFA, MM, AM, MiM, HEN and FFPN, respectively. In general, working under the same liquid and gas flow rates, sensitivities, precision and limits of detection obtained with the FFPN are similar to those obtained with HEN and better than for PFA, MM, AM and MiM nebulizers.