Laser ablation; Raman spectroscopy; Chemometrics; Complementarity; Polymers;INDUCED BREAKDOWN SPECTROSCOPY; INDUCED PLASMA SPECTROSCOPY; ARTIFICIAL NEURAL-NETWORKS; POLYMER IDENTIFICATION; CLASSIFICATION; MICROSCOPY; PIGMENTS; SPECTRA; COPPER; NIR

Classification of plastics is of great importance in the recycling industry as the littering of plastic wastes increases day by day as a result of its extensive use. In this paper, we demonstrate the efficacy of a combined laser-induced breakdown spectroscopy (LIBS)-Raman system for the rapid identification and classification of post-consumer plastics. The atomic information and molecular information of polyethylene terephthalate, polyethylene, polypropylene, and polystyrene were studied using plasma emission spectra and scattered signal obtained in the LIBS and Raman technique, respectively. The collected spectral features of the samples were analyzed using statistical tools (principal component analysis, Mahalanobis distance) to categorize the plastics. The analyses of the data clearly show that elemental information and molecular information obtained from these techniques are efficient for classification of plastics. In addition, the molecular information collected via Raman spectroscopy exhibits clearly distinct features for the transparent plastics (100% discrimination), whereas the LIBS technique shows better spectral feature differences for the colored samples. The study shows that the information obtained from these complementary techniques allows the complete classification of the plastic samples, irrespective of the color or additives. This work further throws some light on the fact that the potential limitations of any of these techniques for sample identification can be overcome by the complementarity of these two techniques.

Stand-off LIBS; heavy metals; environmental samples;INDUCED BREAKDOWN SPECTROSCOPY

Interest in the use of laser-based sensors operating in stand-off mode is increasing due to the wide range of options offered in the evaluation of distant targets. In this work, a stand-off laser induced breakdown spectroscopy (ST-LIBS) system has been developed and demonstrated to determine the heavy elements in soil samples. Initially, different parameters of the device have been optimized in ambient atmosphere and tested for quantitative analysis of Nickel and Chromium at two different stand-off distances (1 m and 6 m). The prepared concentrations were in the range of 100 ppm to 600 ppm. The laser energy of 150 mJ was maintained through out the experiment and to obtain a real time situation the target was in static state.