Selection of Optimum Analytical Lines for the Determination of Several Alloyed Elements in Steel Samples in Glow Discharge Optical Emission Spectrometry with Krypton and Argon

Abstract

The most sensitive emission lines for determination of cobalt, nickel, and vanadium in steel samples were investigated when krypton was employed as an alternative plasma gas in glow discharge optical emission spectrometry. A thorough survey in the emission spectra indicated that more sensitive ionic lines of nickel as well as cobalt, which were free from spectral interference from iron, could be found when using krypton gas instead of argon gas; therefore, the krypton plasma was recommended in the determination of nickel and cobalt in iron-matrix alloy samples. However, the argon plasma yielded more intense ionic lines of vanadium suitable for the vanadium determination in iron-matrix alloy samples. These phenomena could be explained by resonance energy-transfer collisions with the plasma gases which selectively populate different excited levels of these ions between the krypton and the argon plasmas.KEY WORDS: glow discharge optical emission spectrometry; sensitive analytical line; krypton plasma; nickel; cobalt; vanadium.particular emission line and a plasma gas could improve the detection sensitivity in GD-OES, in the case where this resonance condition is fulfilled for the corresponding excited energy level. In this paper, we represent optimum analytical lines for determination of cobalt, nickel, and vanadium in steel samples when krypton is employed as the plasma gas instead of argon. ExperimentalThe Grimm-style glow discharge lamp 18) and the spectrometer system employed 19) have been described in our previous papers. The excitation source was in-house made according to the original model by Grimm. 20) Table 1 summarizes the apparatus and the experimental conditions in detail.Iron-cobalt, iron-nickel, and iron-vanadium binary alloy samples (FXS standard reference materials for X-ray fluorescence analysis, the Iron and Steel Institute of Japan) were employed. Their compositions are 0.52 and 1.06 mass% Ni, 0.50 and 1.02 mass% Co, and 0.49, 1.00, and 2.04 mass% V, respectively. A pure iron plate (99.8 %, purity), a pure nickel plate (99.9 %), a pure cobalt block (99.9 %), and a pure vanadium plate (99.99 %) were also prepared as reference samples. It was polished with waterproof emery papers and then rinsed with ethanol. Before the measurement, pre-discharge was carried out for 5-10 min to remove the surface contaminants. High-purity argon (99.99995 %) or krypton (99.9995 %) was employed as the plasma gas. The pressure of the plasma gas was measured at the vacuum port of the glow lamp with a Prani vacuum gauge, whose readings had been corrected for each gas. Results and DiscussionWe have already conducted a comparative measurement of Ni II emission lines when krypton and argon are employed in GD-OES, based on a discussion on the excitation mechanism, and published a wavelength table for the observed Ni II lines.15) The major Ni II lines are assigned to the 3d 8 4p-3d 8 4s (3d 9 ) transition, whose excitation energies range from 6.39 to 9.39 eV.21) Among them, particular Ni II lines having an excitation energy...