Further insight into analyte transport processes and water vapor, aerosol loading in ICP-OES and ICP-MS

Abstract

Simple concepts that control the amount of analyte, solvent aerosol and solvent vapor that enter the plasma are used to explain changes in analyte transport efficiency as a function of sample uptake rate in pneumatic nebulizer/spray chamber sample introduction systems. These include droplet-droplet collision/coalescence, evaporation of solvent from the sample aerosol and droplet impact on the walls of the spray chamber. We show that even small (2 to 5 μm diameter) droplets have a poor (<12%) transport efficiency through the spray chamber when the sample uptake rate is 1 mL/min. A dual nebulizer system and video are used to assess the role of droplet-droplet collisions/coalescence and aerosol evaporation in controlling sample transport efficiency as a function of sample uptake rate. The impact of water vapor that evaporates from the wall of the spray chamber and from evaporation of solvent from the sample aerosol are described with experimental evidence. Sample transport efficiencies for “conventional” nebulizers and micronebulizers are found to be similar when compared at the same sample uptake rates from 0.02 to 1.0 mL/min. The stability of signals when using “conventional” and micronebulizers at sample uptake rates less than 0.05 mL/min are compared. The impact of water vapor loading and water aerosol loading are investigated using a heated sample introduction system that efficiently evaporates the solvent from aerosol droplets and a vibrating mesh nebulizer than can provide virtually 100% aerosol transport efficiency at aerosol transport rates up to 0.3 mL/min, respectively.