ABSTRACT:
Laser-induced breakdown spectroscopy (LIBS) was employed for simultaneous elemental profiling and plasma diagnostics of commercially available cosmetic products (face blusher and eyeshadow), motivated by growing concerns about toxic metal contamination and associated health risks, including skin irritation, neurological disorders, and carcinogenic effects. Plasma was generated under ambient conditions at atmospheric pressure in air using a Q-switched Nd: YAG laser (532 nm, 5 ns pulse duration, 10 Hz repetition rate). Emission spectra were recorded in the 200–720 nm range, enabling the detection of major and trace elements including Ca, Ti, Mn, Cu, Hg, Cr, Li, Ba, Pb, Na, Fe, Al, and Mg. To ensure reproducibility, spectra were averaged over multiple laser shots at different spatial locations on each sample. Spatially resolved plasma diagnostics were performed to investigate the dynamics of laser–matter interactions. The electron temperature, determined using the Boltzmann plot method under local thermodynamic equilibrium (LTE), decreased from 14,151 K to 5,465 K for sample A and from 13,302 K to 4,157 K for sample B with increasing axial distance. Electron number density, estimated via Stark broadening, ranged from 6.08×10¹⁶ to 1.24×10¹⁶ cm⁻³ and 1.03×10¹⁷ to 1.98×10¹⁶ cm⁻³, respectively, consistent with typical LIBS plasma conditions. Moreover, inverse bremsstrahlung absorption and the plasma frequency were evaluated to understand plasma evolution and energy-coupling mechanisms. The presence of toxic elements such as Pb and Hg emphasizes potential health risks and highlights the importance of rapid screening techniques. The results demonstrate that LIBS is a reliable, rapid, and non-destructive technique for cosmetic safety assessment and quality control.

Keywords: LIBS; Plasma diagnostics; Cosmetic analysis; Electron temperature; Electron density

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