Laser-induced breakdown spectroscopy (LIBS) of animal fat (lard): Efficient sample preparation for onsite analysis and influence of sample temperature on the signal intensity and plasma parameters.

We report an efficient sample preparation method (freezing) for onsite fat and meat analysis via a specially designed thermoelectric cooling and temperature-controlling system. This investigation also focused on the effect of phase change on the sensitivity and reproducibility of LIBS emission signals and plasma parameters. The plasma emissions of animal fats (lard) were recorded when the sample was frozen (-2 °C), fluid (15 °C), and in a liquid state (37 °C) with a thermoelectric cooling system. At each temperature, the plasma emissions were acquired at laser pulse energy from 50 to 300 mJ and detector gate delay (DGD) from 0.5 to 5 µs. With increasing sample temperature, the DGD, where the optical emission intensity reached a maximum, decreased. At a laser pulse energy of 200 mJ and a sample temperature of -2 °C, the emission signals increased fourfold, the signal-to-noise ratio (SNR) improved tenfold, and the self-absorption in the emission lines decreased significantly. The repeatability of the emission signals and plasma parameters of frozen and liquid fat samples was determined using the relative standard deviation (RSD) of Se I (473.08 nm) and K I (766.48 nm) emission lines. The RSDs of the emission signals improved from 40 to 18 % and 37 to 16 %, whereas the shot-to-shot RSDs of the electron temperature and electron number density get improved from 11 to 6 % and 12 to 6.8 %, respectively.

Spectroscopic and crystallographic analysis of nephrite jade gemstone using laser induced breakdown spectroscopy, Raman spectroscopy, and X-ray diffraction.

The elemental composition, mineral phases, and crystalline structure of nephrite jade were investigated using calibration-free laser-induced breakdown spectroscopy (CF-LIBS), Raman spectroscopy, and X-ray diffraction (XRD). For compositional analysis, the laser-induced plasma was generated on the surface of nephrite jade. The plasma emissions were then acquired and analyzed, which revealed several elements in the sample, including Si, Mg, Ca, Li, Fe, Al, Na, K, and Ni. The plasma temperature was extracted from the Boltzmann plot before and after two-step self-absorption correction, and used in CF-LIBS calculations to get the elemental concentration. After self-absorption correction, the quantitative results obtained using CF-LIBS were found to be in close agreement with ICP-OES. The Raman spectrum of nephrite jade exhibits Si-O and M-OH stretching vibrations in the regions of 100 cm-1 to 1200 cm-1 and 3600 cm-1 to 3700 cm-1, respectively, whereas the XRD spectrum revealed the monoclinic crystalline phase of tremolite.