Sensitive detection of trace precious metals in acidic solutions using liquid sheet jet laser-induced breakdown spectroscopy

Rapid in situ analysis of precious metals in liquid has been highly desired for real-time monitoring of recovery processes. We demonstrate that laser-induced breakdown spectroscopy (LIBS) combined with a liquid sheet jet provides a sensitive technique that can directly analyze trace precious metals (Au, Pt, Pd, Ag, Rh, and Ru) in acidic aqueous solutions. A glass slit nozzle resistant to corrosive acids was employed to generate a liquid sheet jet with a thickness of tens of micrometers, which mitigated the liquid splashing inherent in the direct detection of liquid by LIBS, thereby yielding persistent luminous plasma. The optimal thickness of the sheet jet for LIBS measurement was determined to be 14 μm. The LIBS spectral profiles for each analyte obtained by 532 nm laser excitation were explored to select the analytical lines for quantitative analysis. The univariate calibration curves of the analyte elements were then constructed to calculate the limits of detection (LODs) as well as other figures of merit. The LODs of Au, Pt, Pd, Ag, Rh, and Ru were estimated to be 0.62, 0.97, 0.09, 0.14, 0.09, and 0.15 mg L⁻¹, respectively, achieving detection limits below 1 mg L⁻¹ and representing a significant improvement over conventional liquid jet LIBS. Thus, liquid sheet jet LIBS offers a useful tool for real-time monitoring of metal recovery processes.