Elemental Analysis and Comparison of Bulk Soil Using LA-ICP-MS and LIBS methods
Abstract
Elemental analysis methods utilizing Laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) and laser-induced breakdown spectroscopy (LIBS) were developed and used in the characterization of soil samples from the US and Canada as part of a comprehensive forensic evaluation of soils. A LA-ICP-MS method was recently optimized for analysis and comparison between different soil samples in an environmental forensic application [1,2] and LIBS has recently attracted the interest of analytical chemists and forensic laboratories as a simpler, lower cost alternative to the more established analytical methods. In developing a LIBS method, there are many parameters to consider, including laser wavelength, spectral resolution, sensitivity, and matrix effects. The first LIBS method using a 266 nm laser for forensic soil analysis has also been recently reported by our group [3]. The results of an inter-laboratory comparison involving thirteen (13) laboratories conducting bulk elemental analysis by various methods are also reported. The aims of the inter-laboratory tests were: a) to evaluate the inter-laboratory performance of three methods (LA-ICP-MS, µXRF and LIBS) in terms of accuracy (bias), precision (relative standard deviation, RSD) and sensitivity using standard reference materials (SRMs); b) to evaluate the newly released NIST SRM 2710a, which supersedes 2710; and c) to evaluate the utility of LIBS as an alternative technique to LA-ICP-MS and µXRF for bulk analysis of soils. Each sample and standard was homogenized in a high-speed ball mill and pressed into pellets. Participants were instructed to measure the following elements: 7Li, 25Mg, 27Al, 42Ca, 45Sc, 47,49Ti, 51V, 55Mn, 88Sr, 137Ba, 206,207,208 Pb (LA-ICP-MS); Ti, Cr, Mn, Fe, Cu, Sr, Zr, Pb (µXRF); Ba, Cr, Cu, Fe, Li, Mg, Mn, Pb, Sr, Ti, Zr (LIBS). For both LIBS and µXRF, the choice of appropriate spectral lines was determined by the user, optimizing for linearity, sensitivity and precision. Results for both LA-ICP-MS and µXRF were generally consistent for most elements, resulting in good intra-laboratory precision (< 8 % RSD for LA-ICP-MS; < 20 % RSD for µXRF) and low bias (< 10% for LA-ICP-MS; < 35 % for µXRF), which are important characteristics for forensic comparison of soils. Linear calibration curves were also obtained for both µXRF and LIBS. Results for LIBS showed good precision (< 15 %) and bias (< 15 %) for most elements. Limits of detection for trace and minor elements were in the 0.01 - 1 ppm range for LA-ICP-MS and 1 to 200 ppm for LIBS. Finally, the results of a study comparing the bulk elemental composition from soil collected in different locations in Florida and in Canada for the purposes of providing forensic information as part of a broader forensic examination of soil samples are also reported. 1. L Arroyo, T Trejos, P.R. Gardinali, and J.R. Almirall, Optimization and Validation of a LA-ICP-MS Method for the Quantitative Analysis of Soils and Sediments, Spectrochimica Acta Part B: Atomic Spectroscopy, 2009, 64(1), 14-25. 2. L Arroyo, T Trejos, T Hosick, S Machemer, JR. Almirall, and PR Gardinali, Analysis of Soils and Sediments by Laser Ablation ICP-MS: An Innovative Tool for Environmental Forensics, J. of Environmental Forensics, 2010, 11(4), 315-327. 3. SC Jantzi and JR. Almirall, Characterization and forensic analysis of soil samples using Laser-Induced Breakdown Spectroscopy (LIBS), Analytical and Bioanalyt. Chem, 2011, 400(10) 3341-3351.
- Publication:
-
EGU General Assembly Conference Abstracts
- Pub Date:
- April 2012
- Bibcode:
- 2012EGUGA..14.1246A