Compositional analysis of Silybum marianum plant at reduced pressure using calibration-free LIBS

Abstract

Silybum marianum is an annual herb with a wide range of therapeutic values due to its high nutritional content. The compositional analysis of different parts of this plant, such as seeds and leaves, was performed using calibration-free laser-induced breakdown spectroscopy. The optical emission spectra from laser-generated plasma of seeds and leaves revealed the elemental profile, including Mg, Na, Ca, K, Si, Al, Zn, Rb, Sr, Fe, Ti, Ba, C, O, H, and N. The study was focused on improving LIBS based quantitative analysis by reducing self-absorption using two approaches.In the first approach, a theoretical model based on the internal reference line method and the relation between experimental and theoretical broadening was established to reduce self-absorption in the measured spectral line at atmospheric pressure. In the second approach, the self-absorption was evaluated at reduced pressure, which shows considerably reduced for most of the spectral lines at 10 mbar pressure. Thereafter, the theoretical model was applied at reduced pressure to further correct the line intensities. Finally, the self-absorption corrected line intensities were used for the compositional analysis of the plant using one-line CF-LIBS. The analytical results obtained with both approaches show that the results of the theoretical model at a reduced pressure are in close agreement with the ICP-MS results.