Double-pulse and single-pulse laser-induced breakdown spectroscopy for distinguishing between gaseous and particulate phase analytes

We explore the use of a combination of double-pulse and single-pulse laser-induced breakdown spectroscopy (LIBS) methodologies as a means of differentiating between solid-phase and gaseous-phase analytes (namely, carbon) in an aerosol stream. A range of spectral data was recorded for double-pulse and singlepulse configurations, including both ns and fs prepulse widths, while varying the gas-phase mass percentage of the carbon from about 10% to 90% for various fixed carbon concentrations. The carbon emission response, as measured by the peak-to-continuum ratio, was greater for the double-pulse configuration as compared with the single-pulse response and was also enhanced as the percentage of solid-phase carbon was increased. Using a combination of the double-pulse and single-pulse emission signals, a monotonically increasing response function was found to correlate with the percentage of gas-phase analyte. However, individual data points at the measured gas-phase percentages reveal considerable scatter from the predicted trend. Furthermore, the double-pulse to single-pulse ratio was only pronounced with the ns-ns configuration as compared with the fs-ns scheme. Overall, the LIBS methodology has been demonstrated as a potential means to discriminate between gas-phase and particulatephase fractions of the same elemental species in an aerosol, although future optimization of the temporal parameters should be explored to improve the precision and accuracy of this approach.