Improvement of palladium limit of detection by microwave-assisted laser induced breakdown spectroscopy

Detecting elements such as heavy metals is important in many industrial processes. The techniques currently used are time consuming and require excessive sample preparation. In this paper, we demonstrate microwave-assisted laser-induced breakdown spectroscopy (MW-LIBS) to detect palladium (Pd) in solid samples at ambient conditions. Microwave radiation was introduced by a near field applicator to couple the microwave radiation with the plasma. The results were a 92-fold enhancement in palladium signal with 8-fold improvement in the limit of detection at laser energy levels below 5 mJ (1250 J/cm² laser pulse fluence). We also investigate the optimum experimental parameters of palladium detection for both laser-induced breakdown spectroscopy (LIBS) and MW-LIBS. The maximum signal to noise ratio improvement was achieved at microwave power of 750 W and laser pulse fluence of 157 J/cm² for Pd I 340.46 nm. Finally, we examine the location of the near field applicator (NFA) with respect to the sample to show that the MW-LIBS signal strength was significantly affected by the vertical position compared to the horizontal. The detection limits of palladium with LIBS and MW-LIBS were 40 ppm and 5 ppm respectively.