Effect of power and carrier gas flow rate on the tolerance to water loading in inductively coupled plasma atomic emission spectrometry

The effects of the carrier gas flow rate and the power on the amount of water that can be tolerated by the plasma have been studied by ICP-AES. Pneumatic nebulization, ultrasonic nebulization associated with desolvation and laser ablation have been used to obtain wet, partially desolvated and dry aerosols. It has been found that water is beneficial in improving the plasma electron number density and the excitation temperature when so-called robust conditions are used, i.e. high power and low carrier gas flow rate. This can be explained by the release of hydrogen. Under these conditions, desolvation had almost no effect on the plasma characteristics. When non-robust conditions were used, the plasma was highly sensitive to water loading. Desolvation led to an improvement in the plasma conditions. In this instance, the addition of hydrogen was most useful to restore the properties of the plasma and to act as a load buffer to minimize the matrix effects. The plasma characteristics have been evaluated based on simple diagnostics such as the Mg II/Mg I line intensity ratio, the Fe excitation temperature, the Ar line and the Ar continuum.