Monday, November 5, 2007
92-2

Soil Metals Analysis Using Laser Induced Breakdown Spectroscopy (LIBS).

Michael Essington, Galina V. Melnichenko, and Melanie A. Stewart. 2506 E.J. Chapman Drive, Ag Campus, University of Tennessee, Univervisy of Tennessee, Biosystems Eng & Soil Sci., Knoxville, TN 37996-4531

Laser induced breakdown spectroscopy (LIBS) is an elemental analysis technique that is based upon the measurement of atomic emissions generated at a sample surface by a laser-induced microplasma. Although often recognized in the literature as a well-established analytical technique, LIBS remains untested, particularly relative to the quantitative analysis of metals in chemically-diverse samples, such as soils. The objective of this study was to evaluate the capabilities of LIBS relative to the elemental characterization of surface soils. More than 60 surface soil samples from the Pond Creek watershed of east Tennessee where collected and subjected to total dissolution and elemental analysis by ICP. The samples were analyzed by LIBS using an Nd:YAG laser at 532 nm, with a beam energy of 25 mJ per pulse and a pulse width of 5 ns. The wavelength range for the LIBS spectra collection was 200 to 600 nm, with a resolution of 0.012 nm. Elemental spectral lines were identified through the analysis of analytical reagent-grade chemicals and the Kurucz spectral database. The elements that dominated the LIBS spectra were Al, Ba, Ca, Cu, Fe, Mn, Mg, and Ti. The concentrations of these elements were all greater than approximately 500 mg/kg. Numerous other elements were quantified by ICP; however, their concentrations were below detection by LIBS in the 200 to 600 nm spectral range. For quantification, emission lines that were free of interferences were selected and the background- and whole-spectra energy-corrected integrated intensities were determined. The spectral intensities were then compared to the ICP-determined elemental concentrations in order to generate calibration curves for each element. In general, LIBS proved satisfactory for the quantitative analysis of major soil elements (>500 mg/kg), but proved inadequate for the analysis of minor and trace elements.