Simultaneous determination of nitrogen and oxygen in metals by the use of ions with excess kinetic energy using a quadrupole mass spectrometer

Abstract

In the conventional methods for mass analysis of a mixture of nitrogen and carbon monoxide, it is usually required to solve simultaneous equations owing to the effect of multiplication of N⁺ and CO²⁺ ions at m/e=14, otherwise, a high mass resolution mass analyser to be used. In the present study, simultaneous measurement of nitrogen and carbon monoxide extracted from metals was developed with a combination of a vacuum fusion furnace and a conventional low resolution (m/Δm= 56 at m/e= 28) quadrupole mass analyser without any modifications in the ionization chamber such as an additional repeller electrode. The behavior of mass spectra of nitrogen and carbon monoxide was investigated under various ion accelerating voltages. Only ions which have excess kinetic energy were detected at 0 V of ion accelerating voltage, hence an interference of CO²⁺ for N⁺ at m/e=14 was eliminated when carbon monoxide less than 3.6×10^-2 ml (STP) was introduced. The relationships between peak intensities of N⁺, C⁺, and O⁺ and the concentration of nitrogen and carbon monoxide were linear over the range of 0.1×10^-2 to 3.0×10^-2 (STP). By measuring gas extraction curves with programmed temperature {(1020) °C/min}, N⁺, C⁺ and O⁺ ion peaks showed characteristic behavior which gave informations on the states of nitrogen and oxygen in the samples, respectively. The gas extraction curves of metallic chromium and one of the constituents, chromium nitride (Cr₂N), were demonstrated.