A review of laser-induced breakdown spectroscopy for plastic analysis
Introduction
Plastic is composed of a polymer and varying additives that give such substances their chemical and physical characteristics [1]. With the extensive use of plastic products, plastic pollution has become a pressing issue for environmental protection [2], [3]. Currently, manual sorting, Inductively coupled plasma (ICP), Raman spectroscopy, Near-infrared (NIR) spectroscopy, X-ray fluorescence spectrometry, and Atomic absorption spectroscopy (AAS) are frequently used methods for identifying plastic. Manual sorting is a traditional method based on differences in physical properties [4], but it presents some shortcomings such as being error-prone, high-cost, and time-consuming [4], [5]; ICP, which provides efficient atomization, excitation and ionization, has advantages for the analysis of liquid samples with high accuracy [6], while it presents time-consuming steps for sample dissolution prior to the plastic analysis [7]; Raman spectroscopy evaluated as a spectroscopic method can be used to detect molecule bands [8], despite the signal of the Raman spectrum being very weak for plastic analysis [9]; NIR spectroscopy is the most widely used method and meets the sorting requirements for plastic identification [2], [10], however, it cannot be used for colored or opaque plastic (and plastic thicker than 20 microns) analysis [11]; X-ray fluorescence spectrometry provides another sorting technique, with the only advantage of being able to identify polyvinyl chloride by detecting chlorine atoms [2], [12]; AAS has the advantage of higher sensitivity [13], [14], however, it must be crushed and dissolved in liquid, which is tedious and time-consuming [15]. There is a pressing need for developing a newer, faster, and more efficient method for the recycling and quality control of plastic products [16].
Laser-induced breakdown spectroscopy (LIBS) has been developed as a new powerful technology for analytical chemistry [17]. Element-specific lines are emitted from the decay processes of the plasma, detected by a spectrometer, and analyzed by monitoring their positions and intensities to carry out qualitative and quantitative measurements [17]. LIBS has many advantages in the analysis of solid samples including the ability to analyze samples with little or no preparation [18], with a simple method for setting up an apparatus; it is also minimally invasive [19] and high speed [7]. LIBS has been widely used in the metallurgy industry [20], [21], [22], [23], environmental monitoring [24], [25], [26], archeology [27], [28], [29], space exploration [30], [31], [32], [33], geological applications [34], [35], [36], [37], biomedical detection [38], [39], [40], etc. In recent years, LIBS has become a viable tool for the fast detection of colored and polluted plastics in laboratory and field investigations [18], [19], [41]. This review aims to present a discrimination, qualitative and quantitative analysis of plastic and its applications in the plastic field, following a concise description of LIBS instruments used in plastic analysis.
Section snippets
LIBS instruments
LIBS instruments that are used for plastic analysis, as shown in Fig. 1, generally consist of a pulsed laser for generating a plasma, optic systems to concentrate and gather the light, a spectrometer that contains a detector to record the spectrum, extra components that include an object holder and a computer to analyze the spectrum [17]. As listed in Table 1, the most prevalent laser used in plastic analysis is the Nd:YAG (neodymium-doped yttrium aluminum garnet) laser operated at the
Discrimination of plastic
Plastic types studied in published literature include acrylonitrile-butadiene-styrene (ABS), polycarbonate (PC), polystyrene (PS), styrene butadiene (SB), high-density polyethylene (HDPE), polyethylene (PE), polytetrafluoroethylene (PTFE), polyamide (PA), low-density polyethylene (LDPE), polyphenylene oxide (PPO), polyoxymethylene (POM), polyethylene terephthalate (PET), polymathy methacrylate (PMMA), high impact polystyrene (HIPS), polypropylene (PP), thermoplastic polyester (TPO),
Material identification
Material identification is the first stage in the recycling and reuse of plastic waste. Analytical chemistry methods are used for exacting the differences in LIBS plastic spectra, with chemometric methods being popular methods [16], [42], [48], [54], [56], [61], [67], [68].
Selecting suitable spectral variables can improve classification accuracy because analytically useless parts of LIBS plastic spectra are eliminated. Artificial neural networks (ANN) were used for classifying eight types of
Quantitative analysis of plastic
The ultimate goal of any analysis technique is quantitative analysis [19]. Due to the limitation of LIBS instruments in plastic analysis, including the matrix effect and self-absorption effect, the precision of quantitative plastic analysis using a LIBS instrument is relatively lower than other instruments. LIBS quantitative analysis includes calibration and calibration-free method [74].
LIBS applications in the plastic field
In recent years, an increasing number of plastic products have been studied for realizing recycling and quality control of plastic products, with a few studies applied to field applications using On-line LIBS instrument. LIBS was used with an autofocusing unit to quantify the concentration of the toxic elements (Cd, Cr, Hg, Pb, Sb, and Br) in real end-of-life waste plastic pieces, with the use of single- and double-pulse lasers studied to improve sensitivity and limits of detection [7]. LIBS,
Conclusions and perspective
Recent progress for LIBS in plastic analysis was presented in this review, including LIBS instruments used for plastic analysis, discrimination of plastic, qualitative and quantitative analysis of plastic, and LIBS applications in the plastic field. Due to the specific advantages of LIBS, it has become a promising method in fast detection of toxic elements in toys and the recycling of e-waste plastic and food containers.
Material identification using an LIBS instrument is a focus study in
Acknowledgements
The authors are grateful for the financial support from National Major Scientific Instruments and Equipment Development Special Funds (No. 2016YFF0103303 and No. 2011YQ03011302) and National Natural Science Foundation of China (Grant No. 61505066).
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2023, ChemosphereCitation Excerpt :In this context, the use of advanced laser-based analytical techniques, namely laser-induced breakdown spectroscopy (LIBS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), could be a promising approach for the direct analysis of MPs. LIBS can detect different types of plastic due to its unique spectral response to specific polymers (Anzano et al., 2014; Liu et al., 2019; Gajarska et al., 2021), and it showed a good performance in polymer classification based namely on variations in CN and C2 band intensities (Chamradová et al., 2021). LA-ICP-MS, on the other hand, can detect marker metals in polymers (Stehrer et al., 2010; Bonta et al., 2016) and indicate polymer alterations (Brunnbauer et al., 2020).