Investigation of the Effects of Atmospheric Conditions on the Quantification of Metal Hydrides Using Laser-Induced Breakdown Spectroscopy

A study was performed to evaluate the performance characteristics of a laser-induced plasma for real-time determination of various gas-phase metal hydrides, specifically Sn and As. The choice of carrier gas composition and the effect of the pressure on the temporal emission behavior of neutral atoms excited by the laser-induced plasma were investigated. Metal hydrides were generated by using a NaBH4-based hydride generation system. The hydrides were equilibrated into an evacuated cell and isolated from the generator prior to measurement. Laser-induced breakdown spectroscopy (LIBS) spectra of Sn and As were recorded in He and N2 atmospheres at 300 and 760 Torr. The temporal behavior of the LIBS signal was most affected by gas composition, gas pressure, and intensity of the laser beam. The Sn neutral atom emission (284.0 nm) in a N2 atmosphere decreased exponentially with time. In contrast, with a He atmosphere and identical experimental conditions, the Sn signal increased logarithmically with time over the first 100 s. Then the signal maintained a steady-state value until approximately 400 s, after which it decreased exponentially. The steady-state time depends on the concentration of metal hydride. The variation of the LIBS signal with time was mirrored for the As neutral atom emission in He and N2 atmospheres. Various experiments have been performed to find the possible reason for the signal variation with time. It was found that chemical reactions in the laser plasma that might deplete the metal from the gas volume were responsible for the decrease in the signal with time.