Quantification of Eroded Fe Contamination in Plasma Activated Water Using Acoustic Levitation Assisted Laser-Induced Breakdown Spectroscopy by a Novel Method - Multi-Line Calibration Curve

This work reports two different methods of quantifying iron (Fe) in plasma-activated water (PAW) using laser-induced breakdown spectroscopy assisted by acoustic levitation (LIBS-AL). The first method uses external calibration curves (CC) constructed from five different aqueous solutions Fe(NO₃)₃ · 9 H₂O standards with 4, 10, 20, 50, 100 ppm (mg/L). Three Fe II emission lines (238.23, 263.12, 275.58 nm) were chosen to verify the reproducibility and the response of the LIBS-AL technique in a PAW water sample with Fe debris. The limits of detection (LoD) were evaluated down to 1.8 ppm with R² ≥ 0.989. In the second case, multiple emission lines were used in a novel method which was based on a Boltzmann Plot (BP) and the center of mass (for all Fe concentrations) of all BPs were used to create a CC with LoD down to 6.8 ppm. The analysis of PAW prepared by transient spark discharge with electrospray yields Fe concentrations of 23.7 ± 3.0 ppm and 21.7 ± 1.5 ppm from the conventional and the multi-line CC method respectively. This is the first demonstration of LIBS-AL for Fe quantification in PAW. Compared to prior liquid-LIBS, the present approach simplifies sample preparation, avoids nebulizers, substrate contributions, and achieves comparable sensitivity in microliter volumes.