Development and optimization of experimental parameters for the detection of trace of heavy metal (Cr) in liquid samples using laser-induced breakdown spectroscopy technique

Detection of traces of impurities/elements present in liquid samples using laser-induced breakdown spectroscopy (LIBS) is challenging because the signal intensity is weaker than in the case of solid samples. The present paper deals with the optimization of experimental parameters for different phases of a liquid sample and the improvement of the limit of detection (LOD) in these LIBS experimental setups. LIBS spectra of chromium in the liquid sample have been recorded in three different configurations [laminar flow, i.e., liquid flowing through a small jet, frozen liquid (ice), and liquid deposited on a filter paper]. Experimental conditions for different phases were optimized to get a better signal-to-noise (S/N) ratio and signal-to-background ratio (S/B) in the LIBS spectra. The best S/N and S/B ratio is observed when LIBS spectra is recorded for the liquid deposited on the filter paper configuration. The spectral intensity of Cr is enhanced several folds (36 times) in the LIBS spectra recorded in the filter paper configuration as compared to the laminar flow. The calibration curve method is used to measure the LOD for three different configurations. The better LOD (9.7 ppm for 357.8 nm Cr line) is observed in the case of deposited liquid on the filter paper than the other liquid phase (laminar, 85.5 ppm and ice, 63.7 ppm) configurations.