Temporal gating for the optimization of laser-induced breakdown spectroscopy detection and analysis of toxic metals

Optimal temporal gating for laser-induced breakdown spectroscopy (LIBS) analysis was investigated for a select group of toxic metals, namely the Resource Conservation and Recovery Act (RCRA) metals arsenic, beryllium. cadmium, chromium, lead, and mercury. The differing rates of decay between the continuum plasma emission and the atomic emission were used as a means to maximize the signal-to-noise ratio of the atomic emission lines for these six metal species. Detection windows were investigated corresponding to delay times from 2 to 50 mus following the plasma-initiating laser pulse. For the current experimental conditions, it is concluded that the relatively short delay time of 12 mus is optimal for the detection of arsenic, beryllium, cadmium, and mercury, while a longer delay time of 50 mus is optimal for the detection of chromium and lead. The reduced atomic emission intensity at relatively long delay times is compensated for by the use of long detector gate widths. Estimated detection limits are reported for the six metal species based on the optimized temporal gating and ensemble averaging of multiple laser pulses, and the implications for simultaneous metals monitoring are discussed.