2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 7
Presentation Time: 8:00 AM-4:45 PM

Analysis and Discrimination of Volcanic Rocks by Benchtop and Standoff LIBS

GOTTFRIED, Jennifer L.1, HARMON, Russell S.2, HARK, Richard R.3, DE LUCIA Jr, Frank C.1 and MIZIOLEK, Andrzej W.1, (1)Army Research Laboratory, Aberdeen Proving Ground, MD 21005-5069, (2)ARL Army Research Office, PO Box 12211, Research Triangle Park, Research Triangle Park, NC 27709-2211, (3)Department of Chemistry, Juniata College, Huntingdon, PA 16652, hark@juniata.edu

Laser Induced Breakdown Spectroscopy (LIBS)is a simple atomic emission spectroscopy technique capable of real-time, essentially non-destructive determination of the elemental composition of any substance (solid, liquid, or gas). As a technology for geochemical analysis, LIBS is presently undergoing rapid research and development, that has attractive potential for rapid man-portable and/or stand-off analysis in the field. In LIBS, a pulsed laser beam is focused on a sample such that energy absorption produces a high-temperature microplasma. Small amounts of material (picograms-nanograms) are dissociated and ionized, with both continuum and atomic/ionic emission generated by the plasma during cooling. A broadband spectrometer-detector is used to spectrally and temporally resolve the light from the plasma and record the intensity of elemental emission lines. Since the technique is simultaneously sensitive to all elements, a single laser shot can be used to track the spectral intensity of specific elements or record the broadband LIBS emission spectra, which are unique 'geochemical fingerprints' of a material.

In this study, a broad spectrum of volcanic materials was analyzed using both a commercial 'benchtop' LIBS system with broadband detection from ~200-965nm and a developmental 25m 'standoff' LIBS system with broadband detection from ~200-840nm. In each case, broadband LIBS spectra were acquired with a single laser shot. Subsequent classification and discrimination of different volcanic materials (e.g. lavas, tuffs, and tephra) has been achieved with a high degree of success using two different chemometric techniques, ‘soft independent method of class analogy' (SIMCA) and ‘partial least squares discriminant analysis' (PLS-DA).