Aerosol dilution for the introduction of complex matrix samples in plasma-based spectrometry techniques: a tutorial review

Aerosol dilution (AD) is a sample introduction tool that allows the direct analysis of complex matrix samples by plasma-based analytical techniques. In AD, a controlled gas stream (dilution gas) is added at the tertiary aerosol zone, between the spray chamber and the torch. As a result of the dilution of the aerosol, there is an improvement in plasma matrix tolerance and plasma robustness, when compared with pneumatic nebulization without AD. Therefore, solutions with higher total dissolved solids can be introduced with minimal sample treatment for the determination of trace and ultra-trace elements. The use of AD also brings other benefits such as minimization of dilution errors, liquid waste, and sample contamination. A review of the application of AD was conducted, considering more than one hundred papers. An increase in the number of publications was observed after the introduction of AD ICP-MS integrated systems. The effects of AD on plasma, analytical signal, signal/background ratio, and interferences were examined. Strategies for AD ICP-MS optimization that led to its best performance monitored other parameters, such as plasma applied power and sampling depth, in conjunction with the dilution gas flow rate, while maintaining a sum of nebulizer gas and dilution gas flow rates around 1 L min(-1). Additionally, improved operational conditions were obtained by using the signal/background ratio instead of the net signal intensity of analytes. Applications of AD for the analysis of food, environmental, geological, pharmaceutical, biological and clinical samples are also exemplified and discussed. In future studies, AD should be deeper exploited in optical emission spectrometry, chemical speciation, single particle, and laser ablation-based analysis.