Laser Wavelength and Pressure Dependence of Laser Breakdown Time-of-Flight Mass Spectrometry

Abstract

Since the demands for lowering the burdens on the environment will continue to grow steadily, understanding of pollutant emission characteristics becomes more and more important to minimize environmental disruption. These pollutant emission conditions cannot be estimated in real-time using conventional mass-based methods because of their low concentrations in air or exhaust gases. Therefore, new evaluation criteria are required for better understanding of their characteristics. In this study, the laser breakdown time-of-flight mass spectrometry was developed and applied to hydrocarbons to detect the elemental composition of gas phase materials. The laser wavelength dependence of this method was evaluated using 1064 and 266 nm laser outputs. Signals from fragments of hydrocarbons appeared using 266 nm. On the other hand, it was found that the mass spectra of atoms can be detected using the 1064 nm laser breakdown process without intermediate fragment signals. This feature is important to detect atomic signals of the measured materials without the interference of fragmentations. The pressure effect was also evaluated to enhance the detection limit. The higher pressure tends to induce the higher atomic signals. The detection limit can easily reach to ppb or less. The signal intensity was proportional to the concentration of hydrocarbons introduced. The method was applied to various hydrocarbons and the breakdown characteristics of these molecules were taken for the quantitative analysis. Compared with conventional measurements, this method has a lot of merits of the simple signal analysis, real-time and sensitive detection features. The method can cover various industrial applications including the exhaust analysis of combustors, environmental monitoring of air, and plant monitoring for safety and security.