Practical Aspects in the Determination of Gaseous Elements by Radiofrequency Glow Discharge Atomic Emission Spectrometry

Abstract

The determination of gaseous elements such as nitrogen and oxygen in solid samples is complicated by the presence of these elements in the atmosphere. In the case of glow discharge (GD) based methods, introduction of atmospheric gases through vacuum seals or via the discharge gas leads to overestimation of their concentrations in the solid samples and very high background equivalent concentration (BEC) values. The practical considerations necessary for the determination of gaseous elements is demonstrated here in the determination of nitrogen in metals with a radiofrequency glow discharge atomic emission spectrometry (rf-GD-AES) source. Meticulous care in the construction and gas–vacuum plumbing of the rf-GD-AES source can greatly circumvent these difficulties. In addition, the use of ultra high purity (99.999%) discharge gases is shown to be insufficient and further purification by the use of a heated metal (Zr) getter is required. Careful attention to the sample changing protocol also improves system performance. Ultimately, very low background levels of residual gases can be achieved, with concomitant improvements in sputtering rates and plasma stabilization times. Detection limits for nitrogen determinations in a steel reference material are determined to be of the order of 1–10 ppm. Having made these improvements, the data suggest that rf-GD-AES can be used practically for the bulk and depth-resolved determination of gaseous elements (including N, O, and S) in metals and nonconductive materials.