Laser-induced Breakdown Spectroscopy Method Research Articles

Publisher's Note: Correction of article number for Han et al 2024 Plasma Sci. Technol. 26 095502

Due to an editorial error, an incorrect article number was assigned to the Plasma Science and Technology article 'Research on batch multielement rapid quantitative analysis based on the standard curve-assisted calibration-free laser-induced breakdown spectroscopy method' by Weiwei Han et al. The original article number was 000000, however the correct citation is:Weiwei HAN et al 2024 Plasma Sci. Technol. 26 095502The DOI of the article is unchanged: https://doi.org/10.1088/2058-6272/ad5119 The relevant abstracting and indexing services have been informed.

Quantitative Analysis of Pb in Soil Using Laser-Induced Breakdown Spectroscopy Based on Signal Enhancement of Conductive Materials.

Studying efficient and accurate soil heavy-metal detection technology is of great significance to establishing a modern system for monitoring soil pollution, early warning and risk assessment, which contributes to the continuous improvement of soil quality and the assurance of food safety. Laser-induced breakdown spectroscopy (LIBS) is considered to be an emerging and effective tool for heavy-metal detection, compared with traditional detection technologies. Limited by the soil matrix effect, the LIBS signal of target elements for soil heavy-metal detection is prone to interference, thereby compromising the accuracy of quantitative detection. Thus, a series of signal-enhancement methods are investigated. This study aims to explore the effect of conductive materials of NaCl and graphite on the quantitative detection of lead (Pb) in soil using LIBS, seeking to find a reliable signal-enhancement method of LIBS for the determination of soil heavy-metal elements. The impact of the addition amount of NaCl and graphite on spectral intensity and parameters, including the signal-to-background ratio (SBR), signal-to-noise ratio (SNR), and relative standard deviation (RSD), were investigated, and the mechanism of signal enhancement by NaCl and graphite based on the analysis of the three-dimensional profile data of ablation craters and plasma parameters (plasmatemperature and electron density) were explored. Univariate and multivariate quantitative analysis models including partial least-squares regression (PLSR), least-squares support vector machine (LS-SVM), and extreme learning machine (ELM) were developed for the quantitative detection of Pb in soil with the optimal amount of NaCl and graphite, and the performance of the models was further compared. The PLSR model with the optimal amount of graphite obtained the best prediction performance, with an Rp that reached 0.994. In addition, among the three spectral lines of Pb, the univariate model of Pb I 405.78 nm showed the best prediction performance, with an Rp of 0.984 and the lowest LOD of 26.142 mg/kg. The overall results indicated that the LIBS signal-enhancement method based on conductive materials combined with appropriate chemometric methods could be a potential tool for the accurate quantitative detection of Pb in soil and could provide a reference for environmental monitoring.

Research on batch multielement rapid quantitative analysis based on the standard curve-assisted calibration-free laser-induced breakdown spectroscopy method

This study proposes a batch rapid quantitative analysis method for multiple elements by combining the advantages of standard curve (SC) and calibration-free laser-induced breakdown spectroscopy (CF-LIBS) technology to achieve synchronous, rapid, and accurate measurement of elements in a large number of samples, namely, SC-assisted CF-LIBS. Al alloy standard samples, divided into calibration and test samples, were applied to validate the proposed method. SC was built based on the characteristic line of Pb and Cr in the calibration sample, and the contents of Pb and Cr in the test sample were calculated with relative errors of 6% and 4%, respectively. SC built using Cr with multiple characteristic lines yielded better calculation results. The relative contents of ten elements in the test sample were calculated using CF-LIBS. Subsequently, the SC-assisted CF-LIBS was executed, with the majority of the calculation relative errors falling within the range of 2%–5%. Finally, the Al and Na contents of the Al alloy were predicted. The results demonstrate that it effectively enables the rapid and accurate quantitative analysis of multiple elements after a single-element SC analysis of the tested samples. Furthermore, this quantitative analysis method was successfully applied to soil and Astragalus samples, realizing an accurate calculation of the contents of multiple elements. Thus, it is important to advance the LIBS quantitative analysis and its related applications.

Rapid qualitative and quantitative vital nutrient contents in high-altitude cultivated folklore herbal medicinal Costus roots using calibration-free LIBS

Costus Roots (CRs) (Saussurea lappa C.B. Clark- Asteraceae family) is a medicinal herb, very frequently utilized in developing countries for treating worm (nematode) infections, asthma, cholera, digestive problems and in cosmetics products. Due to its widespread consumption in developing countries to determine the health-related essential nutrients and toxic elements is of great significance. This study is highly noteworthy for prominence of therapeutic benefits of the CR roots and public awareness about their harmful effects even for producing herbal drugs derived from its roots. In this study, a very efficient, precise and rapid laser-induced breakdown spectroscopy (LIBS) method was developed to measure the content of the dried and pelletized CRs powder samples. To the best of our knowledge, this is first time that Costus roots have been studied using calibration-free LIBS (CF-LIBS) technique. Initially, the LIBS spectrometer parameters were optimized at 608.3 nm gated-time delay, 35 mJ incident laser pulse energy, and 29 mm laser-to-sample distance (LTSD)) for precise element detection before its application to the CRs analysis. The primary focus of this study is the identification and quantification of various nutrients, such as Ca, K, Mg, Si, S, P, Fe, and Na, as well as relatively toxic elements, such as Al, Ba, Mn, Zn, Sr, B, Cu, Rb, Cr, Ni, Pb, V, and Mo, in addition to Li, Ti in this native CRs herbal medicine. The concentrations of these detected elements (Ca, K, Mg, Si, S, P, Al, Fe, Na, Ti, Ba, Mn, Zn, Sr, B, Cu, Rb, Cr, Ni, Pb, V, Mo, and Li) were successfully determined as 14424, 9511, 2031, 1559, 1450, 1465, 678, 458, 59, 48, 47, 37, 37, 27, 19, 19.6, 15, 2.6, 1.5, 1.5, 1.2, 1.0 and 0.9 mg.kg−1 respectively which was in a excellent agreement with the concentrations measured using the standard ICP-OES technique.

An echellograms-based quantitative analysis method of laser-induced breakdown spectroscopy

The high-resolution broadband LIBS spectrum is typically acquired using an echelle spectrometer and array detectors. However, the full frame (i.e., echellogram) captured by detector is commonly converted to 1D spectrum for the further analysis, which would both limit the detection speed of LIBS and potentially degenerate the analytical performance. In this work, we propose an echellograms-based analysis method for the quantification of minor metal elements in steel. Two metal elements, Mn and Ti, are chosen to validate the feasibility of the analytical method. The LASSO algorithm is used to build the multivariate regression model using LIBS spectra and echellograms respectively. The analytical performance obtained with the echellograms-based model is compared with that of spectra-based model. The efficiency of the echellograms-based quantitative analysis method is demonstrated with better prediction accuracy and precision. Notably, the echellogram-based regression model involves only tens to thousands of pixels from the echellogram, which can be selectively read out using a CMOS detector. The combination of echellogram-based quantitative analysis method and CMOS detector provides new ideas for high-frequency LIBS detection.

Spectroscopic assessment and quantitative analysis of the trace element composition of vegetable additives to meat products

In this scientific work, using the method of laser-induced breakdown spectroscopy (LIBS), the spectra of beef samples and impurities in meat products, namely, banana, pineapple, kiwi, bergamot, poria coconut, Chinese angelica, chicken blood vine, were measured by using developed experimental devices. The purpose of the research was to evaluate the qualitative characteristics of additives to meat semi-finished products for the potential formation of the desired properties of the products due to the analysis of the received spectrograms of trace elements of the samples when applying the LIBS method, quantitative analysis for processing the received information. The determined values of the electron temperature of the plasma, the electron density of the used raw material samples, and the assessment of the local heat balance were used as evaluation criteria. When processing the obtained data, the characteristics of the laser-induced plasma surface of the presented samples were analyzed; the electron temperature and electron density were determined, and a quantitative analysis of trace elements was carried out. LIBS technology allows rapid real-time monitoring and qualitative analysis of trace elements online and over long distances. During the research, it turned out that quantitative analysis requires further study and optimisation of experimental conditions, such as pre-treatment of samples. These conditions optimise defocusing, double laser pulse, and sample temperature, which increases the signal/noise ratio of all spectral lines. The combination of fluorescence spectroscopy and Raman technology enables higher detection sensitivity and better molecule control, creating a quantitative analysis method model that can reduce matrix effects and overcome the self-absorption effect. Among the difficulties of using LIBS technology, several elements can be noted online simultaneously, compared to Raman. The combination of spectroscopy and fluorescence spectroscopy can obtain more comprehensive information about the composition of materials, which can become a potential platform for monitoring trace elements in food products.

Characteristics of laser induced plasma near a flat gas-liquid interface and its effect on the performance of laser induced breakdown spectroscopy (LIBS) detection

Moving the laser focus to the vicinity of the gas-liquid interface is the key point for many new enhanced and new methods to improve the quality of spectral signals in water Laser induced breakdown spectroscopy (LIBS) detection. Understanding the generation and evolution characteristics of the plasma induced by pulsed laser near the gas–liquid interface is of great significance for the establishment of evolution models and improvement of these new LIBS methods. In this paper, a set of slow horizontal flow auxiliary system is established to provide an ideal flat gas–liquid two-phase interface experimental condition. Experimental research on vertical incidence flat system was conducted using techniques such as time-resolved imaging, plasma characterization diagnosis, and spectral analysis. And the detection capabilities of the system were also tested. The characteristics and mechanisms of LIBS near the gas-liquid two-phase interface were investigated with the laser incident on the sample along the vertical direction. Simulation of the laser beam focusing process and observation of laser beam spot images show that the shift of plasma generation position relative to the focal point results from the refraction of the laser beam entering the solution from the air and the ‘interface effect’ of propagation on the vertical direction. Moreover, the plasma forms only the optical power density surpasses the breakdown threshold. In this work, plasma with smaller size, rounder shape, stronger radiation, higher temperature, and higher density can be produced when the focus position is in the liquid column 0.3 mm away from the upper interface. Simultaneously, for example, the Mg ion line at 285.213 nm, the obtained spectral intensity to signal-to-background ratio reaches the maximum value, and a better spectral signal can be obtained, which is 2–4 times of other positions, and the detection limits of the elements Na, Mg, and Ca also reach the lowest level, with 1.6–2.4 times of the detection limit of other focusing positions for Mg and 1.4–1.7 times for Ca, respectively.

Real-time in situ detection of petroleum hydrocarbon pollution in soils via a novel optical methodology

Petroleum hydrocarbon (PHC) contamination in soils is considered one of the most serious problems currently, of which the detection and identification is a fairly significant but challenging work. Conventional methods to do such work usually need complex sample pretreatment, consume much time and fail to do the in-situ detection. This paper set out to create a novel systematic methodology to realize the goals accurately and efficiently. Based on laser-induced breakdown spectroscopy (LIBS) and self-improved machine learning methods, the innovative methodology only uses extremely simple devices to do the real-time in situ detection and identification work and even realize the quantitative analysis of pollution level accurately. In the study, clean soils mixed with petroleum were served as polluted samples, clean soils to be the blank group for comparison. Based on the elemental information from the spectra obtained by LIBS, machine learning methods were improved and helped optimized the algorithm to identify the PHC polluted soil samples for the first time. Furthermore, a novel model was designed to perform the quantitative analysis of the concentration of PHC pollution in soils, which can be applied to detect the degree of PHC contamination in soils accurately. Finally, the harmful volatile component of the PHC polluted soils was also successfully and identified despite its extremely minimal content in the air. The newly-designed methodology is novel and efficient, which has extensive application prospect in the real-time in situ detection of petroleum hydrocarbon pollution.

Laser-induced breakdown spectroscopy for helium detection in beryllium coatings

Laser Induced Breakdown Spectroscopy (LIBS) method is considered to be a promising tool for analyzing the retention of hydrogen isotopes (D and T) and helium (He) on the first walls and divertor regions of future fusion reactors. Helium will be produced in DT reactions but could also be used in the initial non-nuclear phases of DEMO concepts. The present study investigates the He detection by LIBS method in the Be coatings simulating the deposits on the divertor plasma-facing components of JET while the results are also relevant for He detection in the deposits of other wall materials. The study was carried out in a vacuum vessel filled with 2–40 mbar argon background gas. It was shown that 2.8 at. % of He was confidently detectable by LIBS at optimized measurement conditions and the estimated limit of detection at used experimental conditions is approximately 0.7 at. %. The intensity of the He emission line at 587.56 nm was the strongest at the center of the laser-induced plasma plume. The He line intensity increased with the pressure of Ar gas but the broadening of the He line and the increase of the background emission and noise set an upper limit to the Ar background pressure usable for He detection. The application of the calibration-free LIBS procedure resulted in the overestimation of the He/Be ratio by several orders of magnitude. The overestimation can be explained by the deviation of LIBS plasma from the local thermodynamic equilibrium, which is caused by the very high excitation energy of He atoms.

Classification of diverse plastic samples by LIBS and Raman data fusion

The plastic production and usage in the world is steadily increasing. This leads to increased amounts of plastic waste. Most of the waste could be potentially recycled, but only 14 % of plastic waste is recycled. In order to increase the share of recycling in plastic waste management, the recycling process should be completely automated. The problematic part of sorting is being solved by either manual (labor-intensive) or spectroscopy-based (still in development) methods. In this work, we propose the data fusion of Laser-Induced Breakdown Spectroscopy (LIBS) and Raman spectroscopy as a fast, robust, and reliable way to sort/classify any potential polymer material. The sample set of this work consists of several types of polymers in clear, colored, and even mixture versions. So far, no LIBS/Raman classification works involved all these categories in one experiment. Additionally, the low and medium level of data fusion is discussed, and the performance is compared. By using LIBS and Raman data fusion method and both linear and nonlinear chemometric techniques, increased accuracy reaching more than 98 % in the classification of investigated plastic samples was achieved, which was a significant improvement when compared with singular methods classification accuracy.

Comparison of laser-induced breakdown spectroscopy (LIBS) and ICP analysis results for measuring Pb and Zn in soil

Context Laser-induced breakdown spectroscopy (LIBS) is a rapid, multielement analytical technique. It is particularly suitable for the qualitative and quantitative analyses of heavy metals in solid samples. Aims To validate the technique, the LIBS data were compared with the data obtained via conventional inductively coupled plasma (ICP) spectroscopy for the same soil samples. Methods In this study, standard and unknown soil samples from contaminated areas were prepared and fixed to an adhesive tape for LIBS analysis. The soils were also digested with acids for ICP analysis. The emission intensity of one selected line for each of the two analytes, i.e. lead (Pb) and zinc (Zn), was normalised to the background signal and plotted as a function of the concentration values previously determined via ICP analysis. Key results The data demonstrated good linearity for the calibration lines drawn, and the correlation between the ICP and LIBS data was confirmed by the satisfactory agreement between the corresponding values. Conclusions The concentration coefficient of determination (R2) between LIBS and ICP-aqua regia digestion analysis or ICP-total digestion analysis were >0.86 and >0.89 for Pb and Zn, respectively. The total analysis time for the LIBS method was 310 min, which was 54.40% shorter than that for the ICP method (680 min). Implications Consequently, LIBS can be used to measure Pb and Zn in soils without any chemical preparation.

Rapid detection and recognition of phosphors using laser-induced breakdown spectroscopy and principal component analysis method—back propagation neural network algorithm

Rapid detection and quality monitoring of phosphor materials have always been a difficult problem in phosphor materials market. In this work, an independently proposed method based on principal component analysis method—error back propagation neural network algorithm—laser induced breakdown spectroscopy (PCA-BPNN-LIBS) was used for the detection and recognition of phosphors. Firstly, spectroscopic study was carried out on phosphor material samples, and the composition of phosphor elements was analyzed according to the full emission spectrum. Spectral data with different element characteristics detected by LIBS were used as training data sets for further identification. Then PCA method and BPNN algorithm were applied to identify 4 types phosphor samples (P11, P20, P43, P46). A very clear distinction graph was obtained, and the classification accuracy of 99.93% was verified. Allresults show that the proposed PCA-BPNN-LIBS method is an effective method for rapid analysis and recognition of phosphors.

The detection of elemental content changes in electrode coating using laser-induced breakdown spectroscopy

The elemental content of battery electrode coating is prone to change due to the production technology and ambient factors. To ensure the consistent performance and safety of a lithium battery, the elemental content of the electrode coating needs to be kept strictly consistent. This study proposes an internal mixed matrix method that combines laser-induced breakdown spectroscopy and chemometric method to achieve rapid and accurate detection of elemental content changes in electrode coating. The stoichiometric ratios of analytical elements are calculated by using the spectra of laser-induced breakdown spectroscopy. The relationships between that stoichiometric ratios and the actual content of analytical elements are studied and show that they are linear. Thus, the content change of the analytical element can be determined by calculating the change of the stoichiometric ratio. The average relative errors for content changes of iron, lithium, and phosphorus are 6.43%, 2.96%, and 4.12%, respectively, and the lowest detection limits are 278.2 mg/kg, 20.5 mg/kg, and 105.4 mg/kg, respectively. Furthermore, the internal reference method is proposed to correct the effect of ambient gases and improve detection accuracy. The results are that when Fe I 372.751 nm and Fe I 373.485 nm are used as analytical lines, after correcting for the effect of ambient gases, the average relative errors of Fe content changes are reduced by 62% and 72%, respectively, and the lowest detection limits are increased by 67% and 71%, respectively.

Rare earth elements and radioactive elements in black sands from the Konkan and Malabar coasts of India

ABSTRACT The objective of the present work is to demonstrate the ability of the laser-induced breakdown spectroscopy (LIBS) technique for quick detection and quantification of rare earth elements (REEs) and radioactive elements in the black sands at selected locations of the Konkan coast (Goa) and Malabar coast (Kerala) in India. Several REEs such as Ce, Nd, Sm, Dy, Ho, Tm, Gd, and Th have been detected in the LIBS spectra. Calibration-free LIBS method has been used to calculate the concentration of REEs and radioactive elements. The experimental result shows that the concentration of REEs such as Sm, Dy, Ho, and radioactive element Th is maximum in the sands collected from Thiruvananthapuram (Kerala) beach and minimum in the Baga (Goa) beach. The reliability of the results (qualitative and quantitative) obtained by the LIBS method has been examined by other spectroscopic techniques like XRF and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and found to be in close agreement. The multivariate approach (principal component analysis) has been applied to discern the samples based on their spectral data. Photoacoustic spectroscopy and XRD technique are used to detect compounds/minerals of REEs. The relative hardness, degree of crystallinity (DOC), and crystallite size have been calculated.

Investigation of Laser-Induced Cavity and Plasma Formation in Water Using Double-Pulse LIBS

This paper deals with double-pulse laser-induced breakdown spectroscopy (LIBS) underwater, which is a promising analytical method for elemental analysis in the deep sea up to a water depth of 6000 m. A double-pulse laser with a wavelength of 1064 nm is used, which provides a pulse energy of up to 266 mJ for each laser pulse (in single pulse mode), a pulse width of 5–7 ns and a pulse delay in the range of 0.5 to 20 µs. In the double-pulse LIBS method, the first laser pulse creates a cavity on the material surface, and then the second laser pulse forms the plasma in this cavity. It is expected that the plasma is affected by the cavity’s size and lifetime. For this reason, the influence of focus position, pulse energy and pulse delay on the cavity and plasma formation at shallow water depth has been investigated.

Quantitative analysis method of laser-induced breakdown spectroscopy based on temperature iterative correction of self-absorption effect

Laser-induced breakdown spectroscopy (LIBS) is an ideal real-time on-line method of detecting minor elements in alloys. However, in the case of laser-produced high-density plasma, the self-absorption is usually an undesired effect because it not only reduces the true line intensity, leading the line intensity to become nonlinear with the increase of emitting species content, but also affects the characterization parameters of the plasma, and finally affects the accuracy of quantitative analysis. Since the plasma electron temperature <inline-formula><tex-math id="Z-20240228161235">\begin{document}$(T)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231541_Z-20240228161235.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231541_Z-20240228161235.png"/></alternatives></inline-formula>, radiation particle number density and absorption path length (<i>Nl</i> ) determine the degree of self-absorption and affect the corrected spectral line intensity, a new self-absorption correction method is proposed based on temperature iteration. The initial <i>T</i> is obtained by using this method through spectral line intensity, and the self-absorption coefficient SA is calculated based on the initial <i>Nl</i> parameter to correct the spectral line intensity. Then a new <i>T</i> is obtained from the new spectral line intensity and the new SA is calculated to further correct the spectral line intensity. Through continuous calculation and correction of these two parameters, self-absorption correction is finally achieved. The experimental results of alloy steel samples show that the linearity of Boltzmann plot is increased from 0.867 without self-absorption correction to 0.974 with self-absorption correction, and the linear correlation coefficient <i>R</i><sup>2</sup> of the single variable calibration curve for Mn element increases from 0.971 to 0.997. The relative error of elemental content measurement is improved from 4.32% without self-absorption correction to 1.23% with self-absorption correction. Compared with the commonly applied self-absorption correction methods, this method has obvious advantages of simpler programming, higher computation efficiency, and its independence of the availability or accuracy of Stark broadening coefficients. Moreover, this method can directly obtain the radiation particle number density and absorption path length, which is beneficial to the diagnosis and quantitative analysis of plasma.

A novel LIBS method for quantitative and high-throughput analysis of macro- and micronutrients in plants

A novel Laser Induced Breakdown Spectroscopy (LIBS) method enables quantitative and high-throughput analysis of macro- and micronutrients in plants.

Study of the layer thickness of multilayer sample by the LIBS method based on ablation rate correction

As a remote and in situ diagnostic technique for the first wall of tokamaks, laser-induced breakdown spectroscopy (LIBS) has shown promising potential for depth profile analysis of deposition layers on plasma-facing components (PFCs).

Identification and Analysis of Meat Species Using Laser Induced Breakdown Spectroscopy (LIBS): A Review

The high price of beef and its processed products has led to many cases of adulteration with pork, resulting in issues related to halal food assurance. Therefore, it is crucial to conduct identification and analysis of the types of meat used in order to maintain food halalness. One of the methods currently advancing in the identification and analysis of meat types is Laser-Induced Breakdown Spectroscopy (LIBS). The aim of this study is to determine the capability of Laser-Induced Breakdown Spectroscopy (LIBS) in identifying and analyzing various types of meat. The study results indicate that the Laser-Induced Breakdown Spectroscopy (LIBS) method is capable of identifying and analyzing meat types with simple sample preparation and accurate outcomes compared to other methods such as Real Time-PCR, Enzyme-Linked Immunosorbent Assay (ELISA), Electronic Nose System, Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy. The Laser-Induced Breakdown Spectroscopy (LIBS) method can be combined with various chemometric methods such as PCA, PLS, and MSC. Laser-Induced Breakdown Spectroscopy (LIBS) can identify and analyze various types of meat with an accuracy of up to 100% in shrimp and clams mixed sample. In conclusion, the combination of LIBS and chemometric methods demonstrates promising results in identifying and analyzing meat types.

Improving the Laser-Induced Breakdown Spectroscopy for Highly Efficient Trace Measurement of Hazardous Components in Waste Oils.

Improper disposal of waste oils containing hazardous components damages the environment and the ecosystem, posing a significant threat to human life and health. Here, we present a method of discharge-assisted laser-induced breakdown spectroscopy combined with filter paper sampling (DA-LIBS-FPS) to detect hazardous components and trace the source of polluting elements. DA-LIBS-FPS significantly enhances spectral intensity by 1-2 orders of magnitude due to the discharge energy deposition into the laser-induced plasma and the highly efficient laser-sample interaction on the filter paper, when compared to single-pulse LIBS with silica wafer sampling (SP-LIBS-SWS). Additionally, the signal-to-noise ratio and the signal-to-background ratio are both significantly increased. Resultantly, indiscernible lines, such as CN and Cr I, are well distinguished. In contrast with DA-LIBS combined with silica wafer sampling (DA-LIBS-SWS), the spectral signal fluctuations in DA-LIBS-FPS are reduced by up to 33%, because of the homogeneous distribution of the oil layer on the filter paper in FPS. Further examination indicates that the limit of detection for Ba is reduced from a several parts per million level in SP-LIBS-SWS to a dozens of parts per billion level in DA-LIBS-FPS, i.e., nearly 2 orders of magnitude enhancement in analysis sensitivity. This improvement is attributed to the extended plasma lifespan in DA-LIBS and the increasing electron density and plasma temperature in FPS. DA-LIBS-FPS provides a low-cost, handy, rapid, and highly sensitive avenue to analyze the hazardous components in waste oils with great potential in environmental and ecological monitoring.