Acoustic signal in overcoming the matrix effect in LIBS: Toward reliable applicability

Abstract

The versatility of laser-induced breakdown spectroscopy (LIBS) resulting from its advantageous analytical characteristics is, unfortunately, still limited by challenges inherent to the fundamental principles of the method – the processes of laser ablation and laser-induced plasma generation. Unwanted effects (generally known as matrix effects) significantly decrease the analytical performance of LIBS, complicating quantification and impairing reproducibility.

This study investigates acoustic signals accompanying plasmas (LIPAc) to overcome these limitations and enhance LIBS performance. The influence of instrumental (microphone types), operational (laser wavelength and fluence) and sample parameters on acoustic responses were evaluated. The results indicate that laser fluence strongly influences acoustic wave oscillation. When laser fluence substantially exceeds the breakdown thresholds of the different components in the matter, acoustic responses may become identical across various materials. On the other hand, proportionality in differences of acoustic signal is maintained for different microphones and laser wavelength settings.

Promising solutions for eliminating matrix effects on various surfaces were identified, but the suitability and efficiency may be highly dependent on the emission line used. This is demonstrated using the signals of atomic Cu(I) 324.74 nm and ionic Cu(II) 329.04 nm lines measured from an aluminum sample with a partially coppered and partially roughened surface.

Acoustic maps of a galena ore sample demonstrate the applications of LIPAc in spatially resolved LIBS imaging and elemental mapping. These maps can help eliminate the discrepancy between the intensities of the calcium atomic line of Ca(I) at 422.67 nm measured from the galena mineral and calcium carbonate.