Enhancing the sensitivity of laser-induced breakdown spectroscopy for liquid samples by selecting an appropriate substrate and its temperature

The elemental analysis of liquid samples plays a vital role in understanding biological and environmental processes; however, their direct investigation using laser-induced breakdown spectroscopy (LIBS) often results in poor reproducibility and weak plasma emission due to splashing and evaporation. In this work, a liquid-to-solid conversion LIBS technique was employed to enhance detection sensitivity. Aqueous potassium chloride solutions with concentrations ranging from 7.45 to 0.0745 µg/ml were deposited on three metallic substrates, i.e., aluminum (Al), molybdenum, and tungsten and were analyzed using a Q-switched Nd:YAG laser (1064 nm, 8 ns, 1 Hz). The influence of substrate type on detection sensitivity was systematically investigated. Among the tested substrates, Al exhibited the highest potassium spectral intensity with an improved limit of detection of 182 ng/ml. The superior performance of Al was attributed to its high thermal conductivity and low ionization potential, which facilitated efficient plasma generation. Additionally, the Al substrate temperature was varied from 25°C to 300°C to explore the impact of temperature on the detection sensitivity of potassium. As the temperature increased, the surface reflectivity of Al decreased, leading to higher electron temperature and electron density. The results showed that the limit of detection also increased significantly, reaching 8.48 ng/ml at 300°C. These findings highlight the importance of substrate type and its temperature for elemental analysis of liquid samples, providing a promising alternative for highly sensitive elemental detection.