Nitrogen Determination in Argon by Surface-Wave-Induced Plasma Atomic Emission Spectrometry

Abstract

An on-line analyzer for traces of nitrogen in argon was developed with the use of microwave-induced plasma/atomic emission spectrometry (MIP-AES). The plasma is generated with a surface wave launcher called “Surfatron.” The emission spectra of the major impurities of argon were characterized in the spectral region from 600 to 900 nm. Effects on analyte emission of parameters such as observation height in the plasma, gas flow and pressure, applied power, and discharge tube geometry were studied. A charge-coupled device (CCD) was used as the multichannel detector for this analyzer. The automation of the CCD by a microcomputer allowed fast, unaided data acquisition and analysis, and the overall system had the compactness, ruggedness, and stability essential for on-line use. We measured a 0.4-ppm detection limit for nitrogen, and the system's long-term stability is greater than 99%. Also, comparative work with a commercial photodiode array (PDA) system was conducted, and a 0.05-ppm detection limit for nitrogen was obtained.