Characterization of aerosols produced by pneumatic nebulizers for inductively coupled plasma sample introduction: effect of liquid and gas flow rates on volume based drop size distributions

Abstract

The effect of liquid sample uptake rate and nebulizer gas flow rate on analyte transport rates and volume based primary and tertiary drop size distributions were studied for two pneumatic, concentric nebulizers with a Scott type spray chamber. Experimentally measured Sauter mean diameters and spans were compared to those predicted by an empirical model. One of the two nebulizers produced analyte transport rates that were a factor of two or more higher than the other nebulizer under all uptake rate and gas flow rates studied, despite that the nebulizers were of the same model. When the sample uptake rate is increased 400% (from 0.4 to 2.0 ml/min) the aerosol transport rate increased by only 60 to 68%. Losses of aerosol of all drop sizes due to secondary and tertiary processes result in a decrease in the sample transport efficiency as the uptake rate is increased. When the nebulizer gas flow rate was increased from 0.4 to 1.0 l/min the analyte transport rate increased more than a factor of five. The increase in analyte transport rate (and efficiency) as the gas flow rate was increased from 0.4 to 0.6 or 0.7 l/min was due to both a larger volume of small primary aerosol drops produced and less severe losses of drops due to secondary and tertiary processes. The relative increase in volume of small primary aerosol drops produced when the nebulizer gas was increased from 0.6 or 0.7 to 1.0 l/min was similar to the relative increase in analyte transport rate. The higher transport rates produced by one of the two nebulizers was due to a higher production/loss ratio due to secondary and tertiary processes for drops of all sizes less than 20 μm in diameter rather than differences in the volume of primary aerosol contained in small drops.