A calibration-free approach for on-site multi-element analysis of metal ions in aqueous solutions by electrodeposition-assisted underwater laser-induced breakdown spectroscopy

We investigate the possibility of on-site multi-element analysis of part-per-million order Cu2 + and Zn2 + in an aqueous solution by underwater laser-induced breakdown spectroscopy (underwater LIBS) of a Pt electrode on which Cu2 + and Zn2 + are electrodeposited in advance. Atomic emission lines of Cu and Zn are simultaneously observed. To apply a calibration-free LIBS (CF-LIBS) approach to the present system, we estimate the Zn/Cu ratio in the laser ablation plasma from the emission spectra. Although the Zn/Cu ratio in the deposit agrees with the ratio in the solution, the ratio in the plasma considerably deviates from the ratio in the deposit. We demonstrate the possibility of quantitative analysis even in such a case by correcting the deviation using a simple model considering heat propagation and thermal evaporation during liquid-phase laser ablation.