On-Line Sorting of Wood Treated with Chromated Copper Arsenate Using Laser-Induced Breakdown Spectroscopy

Abstract

This paper details the design, implementation, and field evaluation of an online detector system using laser-induced breakdown spectroscopy (LIBS) for the analysis of copper chromated arsenate (CCA) treated wood products. The LIBS-based instrument functioned by creating the laser-induced plasma directly on the sample surface while wood was translated under the detector system, and was successful in discriminating between CCA treated wood and untreated wood products based on the atomic emission signal of chromium. The system was optimized for plasma emission collection both in and out of the laser focal plane and temporally optimized for chromium analysis using a compact, non-intensified charge-coupled device (CCD)/spectrometer unit. Using either single laser pulse spectra or 5-shot and 10-shot spectral averages, the accuracy of LIBS-based analysis ranged from 92 to 100% for identifying both CCA treated and untreated wood samples from the waste stream at a construction and demolition debris recycling center. Additional implementation issues are discussed in the context of LIBS-based on-line sorting of construction and demolition wood debris.