Detection of manganese in solution in cavitation bubbles using laser induced breakdown spectroscopy

Levels of dissolved manganese in water samples down to 80 μg/l are measured using emission spectroscopy. Optical emission spectroscopic methods tend to be insensitive in liquids due to strong quenching processes. Laser induced breakdown spectroscopy (LIBS) within a cavitation bubble overcomes this restriction. The output of a double pulsed Q-switched Nd:YAG laser, operated at 532 nm, is coupled to an optical fibre. The fibre guides the laser pulses to a silicon target immersed in a water sample contaminated with manganese. The cavitation process is initiated with the first laser pulse. At maximum bubble expansion, the second laser pulse ignites the plasma in the vapour/gas-filled cavitation bubble. Emission is collected by an additional optical fibre located near the bubble. Characteristic spectral line intensities of manganese are recorded and correlated to an internal calibration standard. Spectral analysis and data acquisition are carried out using an image-intensified optical multi-channel analyser.