LIBS—A NEW CHEMICAL ANALYTICAL TECHNOLOGY FOR THE IN-FIELD ANALYSIS OF TRACE METALS

Laser-induced breakdown spectroscopy (LIBS) is an emerging technology for minimally-destructive, in-situ chemical analysis in which a solid-state, short-pulsed laser is focused on a sample to generate a high-temperature plasma. Upon cooling, the excited atomic, ionic, and molecular species produced in the plasma emit radiation that is characteristic of the elemental composition of the volatilized sample. A laboratory bench-top LIBS system at the Army Research Laboratory has been used to survey trace metals in a variety of geomaterials including rocks, soils, ores, and desert rock varnish. A field-portable LIBS system has been developed by ADA Technologies for real-time environmental analysis, based upon the use of a hand-held laser-bearing fiber optic probe and a briefcase-size analyzer system containing a spectograph with a thermoelectrically-cooled 250x12 element CCD, that can be powered by either a 115V AC current or a 12V battery. The field-portable LIBS unit, which has a 20nm spectral range, was purposely designed for the detection of Pb. It has been field tested and demonstrated using both the 220.4 nm and 405.8 nm Pb emission lines for soils contaminated with Pb from (i) the demilitarization of small-arms ammunition by burning at Sierra Army Depot, CA and (ii) the leaching of exterior painted surfaces of buildings at Fort Carson, CO. The portable unit has also been used to detect Pb on PM-10 air filters from local air monitoring stations in Panama City, Panama, and to stratigraphically profile through layers of paint on interior surfaces in a WWII-era building at Fort Carson, CO. Work is presently in progress to optimize the instrument for rapid, in-situ surveying and the quantitative assessment of trace metals across the wide range of natural field environments and conditions in which this new technology might be expected to operate.