Analysis of Heavy Metal Pollution in Soil Using Transversely Excited Atmospheric CO2 Laser-Induced Plasma by Trapping the Soil in Microstructured Holes on Metal Subtargets

Abstract

A unique technique for direct analysis of soil samples utilizing a special advantage of a transversely excited atmospheric (TEA) CO2 laser-induced plasma generated at atmospheric pressure on a metal target has been developed. In this technique, a metal subtarget, such as nickel plate, structured with intentional microholes on its surface, each with dimensions of around 100 μm in diameter and depth, was used to selectively trap small sized soil particles by immersing the metal plate subtarget into the polluted soil sample. The trapped small soil particles on the metal subtarget were irradiated by a TEA CO2 laser (10.6 μm, 1.5 J, 200 ns) at atmospheric pressure under defocused condition with a spot size of 3 mm × 3 mm. This trapping and confining scheme substantially suppresses the blowing off effect; thus, the trapped soil particles can effectively be dissociated and atomized in the microstructured holes. Using this method of a microstructured metal plate subtarget, quantitative analysis was carried out on loam soil samples polluted by Pb. A linear calibration curve was obtained with a detection limit of approximately 50 mg/kg. Preliminary quantitative studies were carried out for a quartz sand sample containing Cr and Hg, resulting in linear calibration curves with detection limits of approximately 25 mg/kg and 10 mg/kg, respectively, at this stage. This technique is promising as a potential field screening tool for soil analysis.