Analytical Sciences

Spectroscopic Characteristic and Analytical Capability of Ar–N₂ Inductively Coupled Plasma in Axially Viewing Optical Emission Spectrometry

Masaki OHATA

Inorganic Standard Group, Research Institute for Material and Chemical Measurement, National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8563, Japan

The spectroscopic characteristics and analytical capability of argon–nitrogen (Ar–N₂) inductively coupled plasma (ICP) in axially viewing optical emission spectrometry (OES) were examined and figures of merit were determined in the present study. The spectroscopic characteristics such as the emission intensity profile and the excitation temperature observed from the analytical zone of Ar–N₂ ICP in axially viewing ICPOES, in order to elucidate the enhancement of the emission intensity of elements obtained in our previous study, were evaluated and compared to those of the standard ICP. The background and emission intensities of elements as well as their excitation behavior for both atom and ion lines were also examined. As results, a narrower emission intensity profile and an increased excitation temperature as well as enhancements for both background and emission intensities of elements, which could be due to the ICP shrunken as well as the enhancement of the interaction between the central channel of the ICP and samples introduced, were observed for Ar–N₂ ICP in axially viewing OES. In addition, the elements with relatively higher excitation and ionization energies such as As, Bi, Cd, Ni, P, and Zn revealed larger enhancements of the emission intensities as well as improved limits of detection (LODs), which were also attributed to the enhanced interaction between Ar–N₂ ICP and the samples. Since the Ar–N₂ ICP could be obtained easily only by the addition of a small amount of N₂ gas to the Ar plasma gas of the standard ICP and no optimization on the alignment between Ar–N₂ ICP and the spectrometer in commercially available ICPOES instruments was needed, it could be utilized as simple and optional excitation and ionization sources in axially viewing ICPOES.

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