Effect of operating conditions on excitation temperature and electron number density in axially-viewed ICP-OES with introduction of vapours or aerosols

Abstract

The combined effect of the power and the carrier gas flow rate on excitation temperature, electron number density, ionic-to-atomic line intensity ratios and departure from local thermal equilibrium has been studied in an axially-viewed plasma with introduction of different amounts of wet aerosols, partially desolvated aerosols or dry vapours, according to empirical modelling and experimental design methods. Under robust conditions (1500 W and a carrier gas flow rate of 0.7–0.85 L min⁻¹), an increase in water loading led to an improvement in the plasma excitation properties, while desolvation caused degradation. In contrast, under non-robust conditions, the plasma was no longer able to tolerate an increase in water loading and desolvation resulted in an improvement in the plasma characteristics. The hydrogen formed during the hydride generation process significantly improved the plasma excitation properties, regardless of the conditions. In this instance, the plasma characteristics were primarily affected by the reductant concentration, which determined the amount of hydrogen generated, and by the carrier gas flow rate, which controlled its residence time within the plasma. In contrast, there was no relevant change in the plasma excitation conditions due to systematic variation of HCl concentration from 0.1 to 6 M.