Analysis of preservative-treated wood by multivariate analysis of laser-induced breakdown spectroscopy spectra B Madhavi Z. Martin a , Nicole Labbe ´ b, * , Timothy G. Rials b , Stan D. Wullschleger a a Environmental Sciences Division Oak Ridge National Laboratory, P.O. Box 2008 MS 6422, Oak Ridge TN 37831-6422, USA b Forest Products Center, University of Tennessee, 2506 Jacob Drive, Knoxville, TN 37996-4570, USA Received 8 February 2005; accepted 17 May 2005 Available online 27 June 2005 Abstract In this work, multivariate statistical analysis (MVA) techniques are coupled with laser-induced breakdown spectroscopy (LIBS) to identify preservative types (chromated copper arsenate, ammoniacal copper zinc or alkaline copper quat), and to predict elemental content in preservative-treated wood. The elemental composition of the samples was measured with a standard laboratory method of digestion followed by atomic absorption spectroscopy analysis. The elemental composition was then correlated with the LIBS spectra using projection to latent structures (PLS) models. The correlations for the different elements introduced by different treatments were very strong, with the correlation coefficients generally above 0.9. Additionally, principal component analysis (PCA) was used to differentiate the samples treated with different preservative formulations. The research has focused not only on demonstrating the application of LIBS as a tool for use in the forest products industry, but also considered sampling errors, limits of detection, reproducibility, and accuracy of measurements as they relate to multivariate analysis of this complex wood substrate. D 2005 Elsevier B.V. All rights reserved. Keywords: Laser induced breakdown spectroscopy; Multivariate analysis; Preservative-treated wood; Inorganic components 1. Introduction The forest products industry, which encompasses the production of wood, pulp, paper, and engineered wood products, is increasingly using spectroscopic-based techni- ques to assess product quality and to facilitate on-line process monitoring and control. Various techniques have been used to assess the structural behavior of wood and engineered wood products, and several high-throughput spectroscopic techniques have shown promise in providing information on the chemical, physical, and mechanical properties of paper, wood, and wood products [1–4]. Such activities have focused almost exclusively on characterizing the organic constituents of wood (i.e., cellulose, hemi- celluloses, lignin and extractives), with few studies address- ing the inorganic composition of wood or engineered wood products. Atomic absorption spectroscopy was used in early studies to analyze the elemental composition of wood digests [5], but the technique has received limited use presumably due to high detection limits and the inability to perform multi-element analyses. Other techniques have been used to assess the elemental composition of wood and wood products, including photon-induced X-ray emission spec- troscopy, secondary ion mass spectroscopy, and laser- ablation ICP-MS [6], but these too suffer from a unique set of practical and technical limitations. One spectroscopic-based approach that has been used successfully to assess the inorganic composition of wood and wood products is laser-induced breakdown spectroscopy (LIBS), which has been used for the detection of heavy metals in preservative-treated wood [7–10]. The primary preserva- tive for residential application has been chromated copper arsenate (CCA), but other preservatives such as ammoniacal 0584-8547/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.sab.2005.05.022 B This paper was presented at the 3rd International Conference on Laser Induced Plasma Spectroscopy and Applications (LIBS 2004), held in Torremolinos (Ma ´laga, Spain), 28 September – 1 October 2004, and is published in the special issue of Spectrochimica Acta Part B, dedicated to that conference. * Corresponding author. Tel.: +865 946 1124; fax: +865 946 1109. E-mail address: nlabbe@utk.edu (N. Labbe ´). Spectrochimica Acta Part B 60 (2005) 1179 – 1185 www.elsevier.com/locate/sab