Aerosol measurements with laser-induced breakdown spectroscopy and conditional analysis

The methodology referred as to Conditional Analysis for sampling of aerosols was first evaluated and verified, and then revisited to include the possible case where the analyte emission intensities are affected by low particle sampling rates, and low-intensity analyte emission lines are observed in the single-shot spectra. Calcium-bearing aerosol streams with a Ca mass concentration from 36.3 to 182.5 μg/m³ and 3.6 and 18.2 μg/m³ were generated and analyzed with a LIBS probe that employed a 28.3-mJ laser beam and sampled the aerosol flow at 5 Hz. Average relative errors of 16.0 and 18.4% were obtained for each concentration range with the use of Conditional Analysis. A modified version of Conditional Analysis was developed by involving the experimental particle sampling rates in an earlier stage of the overall calibration and analyte determination. With such approach a general reduction of the relative errors was obtained, and an average relative error of 10.7% was obtained for 4 test samples prepared independently. A minimum detectable mass of approximately 8 fg was calculated using the LIBS models of discrete particle sampling; and the Ca limit of detection was determined as 0.45 μg/m³ (0.3 ppb) based on calibration curves.