Sensitive determination of rare earth elements in liquid samples by spatial confinement assisted surface enhanced laser-induced breakdown spectroscopy

The rapid determination of rare earth elements (REEs) in liquid samples holds significant importance for various applications such as the exploration and development of REEs resources, quality control of the extraction process, regeneration and recycling of REEs, and monitoring of nuclear industry wastewater. This study employed spatial confinement assisted surface-enhanced laser-induced breakdown spectroscopy (SC-SE-LIBS) for REEs determination in liquid samples. Investigations were conducted into the impact of different material substrates, sample pretreatment methods, and spatial confinement cavity diameters on detection performance. The results reveal that the graphite substrate yields superior spectral signal intensity compared to other materials (Zn, Al, and Ni). The groove-constrained liquid–solid conversion (GCLSC) pretreatment method significantly enhances spectral stability and detection accuracy. The most favorable signal enhancement is achieved using a cylindrical spatial confinement cavity (CSCC) with an 8 mm diameter. Employing the optimized experimental conditions, quantitative analysis of six REEs (La, Ce, Pr, Nd, Gd, Y) in liquid samples was performed using analytical lines at wavelengths of La Ⅱ 394.91 nm, Ce Ⅱ 401.24 nm, Gd Ⅱ 404.99 nm, Nd Ⅱ 406.11 nm, Pr Ⅱ 417.94 nm, and Y Ⅱ 488.37 nm. The obtained calibration curves exhibited R2 fit coefficients above 0.99, with corresponding limits of detection (LoDs) of 0.021 μg/mL, 0.104 μg/mL, 0.312 μg/mL, 0.241 μg/mL, 0.036 μg/mL, and 0.045 μg/mL, respectively.