The effects of organic gases on atomic spectrometric signals in the ICP

Abstract

Over the past several decades, the inductively coupled plasma (ICP) has become one of the analytical chemist’s most popular tools. The principal use of the ICP has been as an excitation cell for atomic emission spectrometry (AES). More recently, it has been used as an atomization cell for atomic fluorescence spectrometry (AFS). Since the ICP is an energetic source, the vaporization process is efficient. This high temperature promotes transitions of the analyte and the argon support gas making spectral interference a problem. To alleviate this problem in AFS, it was necessary to look higher in the plasma tail, now the entrainment of oxygen and the formation of metal oxides was thought to be occurring. It was proposed that the addition of an organic gas may reduce the metal oxides, thus increasing the free atom concentration. The addition of propane produced enhancements of AFS signals in the ICP.

In this study, the addition of propane and butane depressed many AES signals. In an attempt to elucidate a mechanism for the observed discrepancies, electron number density, excitation temperature, ion temperatures, atomic emission and atomic absorption measurements were considered. The system used enabled observations to be made on the effects of organic species in the plasma without altering the analyte transport efficiency.

Using atomic absorption, scatter free data was obtained for the effects of propane on the ground state atom population, and it was observed to increase the ground state atom concentration for all elements attempted, with the exception of silver. With slurry introduction into the ICP, it was possible to control the composition of the plasma tail plume. The results from the slurries indicated that molecular formations can occur in the ICP. Finally, it was determined that a relationship between excitation energy and the effects of propane existed, and the increased ground state was due to propane hindering the excitation process of the plasma.