Isotopic analysis of zinc plasma using Laser‒Ablation Time‒of‒Flight mass spectrometer

Abstract

In this study, we present the isotope analysis of zinc plasma using laser ablation time-of-flight mass spectrometry (LA-TOF-MS). The isotopes were detected based on their mass-to-charge (m/z) ratio. To improve the resolution of LA-TOF-MS, an aluminum disk with a 1 mm central opening was placed within a cylindrical magnetic filter (∼1 T) along the ion signal path. The electric field was applied using DC power, and the signal-to-noise ratio was monitored via an oscilloscope. Zinc isotopes; Zn-64, Zn-66, and Zn-68 were observed with high resolution within 1 μs by systematically applying electric fields in the ionization and extraction regions. The full-width half maximum (FWHM) significantly decreased with increasing electric field strength, from 0.215 to 0.137 μs for Zn-64, 0.294 to 0.146 μs for Zn-66, and 0.239 to 0.190 μs for Zn-68. The mass concentrations for Zn-64, Zn-66, and Zn-68 were estimated to be 48.6 %, 27.9 %, and 18.8 %, respectively, within ±0.1 % uncertainty, which is in agreement with the reported values in the literature. Laser-induced breakdown spectroscopy (LIBS) is used for plasma characterization and rapid qualitative identification of the constituent elements in the sample under study. Energy-dispersive X-ray (EDX) spectroscopy is applied for the cross-validation of the qualitative results obtained using LIBS. Since spectroscopically pure zinc was used in this study, spectral lines of any impurity elements may also appear in both spectra. However, LA-TOF-MS yields peaks along the arrival time scale of the constituent ions in the sample. The results demonstrate that LA-TOF-MS, combined with LIBS and EDX techniques, suggest a rapid method for elemental/isotope analysis.