ArF Laser Induced Plasma Spectroscopy of Lead Ions in Aqueous Solutions: Plume Reheating with a Second Nd: YAG Laser Pulse

Laser-induced breakdown spectroscopy (LIBS) is a versatile technique for elemental analysis. Its sensitivity may not be impressive, but we recently showed that the detection limits for metal ions in aqueous solutions could be improved if an ArF (193 nm) laser was used for ablation.1 The plasma temperature could be maintained at about 0.35 eV for several ms, which was near optimal for ‘soft’ transitions such as the Na 589 nm line. Accordingly, detection limits as low as 0.4 ppb were demonstrated. For ‘hard’ transitions like the Pb 405.8 nm line, however, the plasma was cooler than ideal and the detection limit was only about 300 ppb. The detection limit would be even poorer if the sample solution did not absorb at 193 nm. This shortcoming might be overcome if the cooling plume was reheated by a second laser pulse.2–5 The plasma temperature could be raised and the sensitivity enhanced. In this short note, we report on the application of laser rekindling to the LIBS analysis of Pb in aqueous solutions.