Laser-induced Breakdown Spectroscopy Detection Research Articles

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

Abstract 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 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 plane 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.

Blank sample denoising algorithm (BSDA): An effective spectral noise reduction in water sample LIBS detection

Laser-induced breakdown spectroscopy (LIBS), as an elemental composition analysis technique, has many unique advantages and great potential for applications in water detection. However, the quality of LIBS spectral signals, such as signal-to-noise ratio and stability, is often poor due to the matrix effects of water, limiting its practical performance. To effectively remove the inherent weak radiation in experimental spectral data that can be easily mistaken for noise, this paper proposes a denoising algorithm for processing spectral data using a self-built blank sample spectral database of deionized water samples, and designs a complete data processing workflow. It includes steps such as blank sample data screening, internal standard correction, blank sample correction, and spectral smoothing. Against the backdrop of marine applications, experimental spectral data for target elements Na, Mg, Ca, K, Sr, and Li were processed with this algorithm. The results show that after algorithm processing, the spectral quality was significantly improved, with the signal-to-noise ratio and detection limits of various elements improved by at least one order of magnitude. The signal-for Li increased by up to 36 times, and the detection limit for K decreased by up to 25.2 times. Additionally, tiny spectral peaks that could not be observable in the original spectral data could be effectively extracted after processing. From a technical implementation perspective, the database establishment and data process are simple and practical, with universal applicability. Therefore, this method has good potential and wide foregrounds in many other water sample LIBS detection technologies.

Study on laser-induced breakdown spectroscopy in high-pressure helium gas environment for deep ocean applications

Laser-induced breakdown spectroscopy (LIBS) has gained wide acceptance as an in situ detection technique for elements. However, in deep-sea applications, the sensitivity of LIBS detection will be reduced due to the high-pressure environment and the nature of water. To address the negative effects of high-pressure water, this study used the method of draining the water from the sample surface by passing high-pressure helium gas, which allowed the plasma excitation environment to be converted from high-pressure water to high-pressure gas. The available spectral signals of solid samples at 60 MPa gas pressure were obtained for the first time, and the peak intensity and spectral broadening of the spectral lines at different pressures were analyzed for comparison. We found a nonlinear decrease in the spectral intensity and a gradual increase in the spectral broadening during the pressure increase. We also investigated the effect of laser energy on the intensity and width of the spectral lines in a high-pressure helium environment and found that increasing the laser energy in a high-pressure environment enhanced the spectral intensity and that the change in laser energy almost did not affect the line width. Finally, by observing the plasma images at different pressures with different energies, this study found that the laser penetrated the high-pressure helium gas in advance and leaved a column of light in the gas, and the plasma was slowly made smaller as the ambient pressure increases. This finding explained the cause of laser energy loss and demonstrated that the LIBS signal intensity can be improved by increasing the laser energy and shortening the laser transmission distance in a high-pressure gas environment.

Detection of trace phosphorus in water by plasma amplification laser-induced breakdown spectroscopy.

For monitoring the extent of eutrophication in water, phosphorus (P) was detected by laser-induced breakdown spectroscopy (LIBS). A plasma amplification method was proposed and the filtered aerosol was guided to interact with the collinear laser in conjunction with a nebulizer, cyclonic spray chamber, and quartz tube. With this method, the length of the plasma was amplified from 5.27∼8.73 to 17.58 mm. Moreover, the limit of detection (LoD) values of P in water improved from 6.13∼17.75 to 3.60 ppm. Furthermore, the average relative error (REAV) values reduced from 10.23∼23.84 to 6.17%. The root mean square error of cross-validation (RMSECV) values decreased from 16.68∼64.29 to 3.24 ppm. This demonstrated that plasma amplification LIBS could improve the quantitative analysis performance of LIBS detection of trace phosphorus in water.

Full-Stokes polarization laser-induced breakdown spectroscopy detection of infiltrative glioma boundary tissue.

The glioma boundary is difficult to identify during surgery due to the infiltrative characteristics of tumor cells. In order to ensure a full resection rate and increase the postoperative survival of patients, it is often necessary to make an expansion range resection, which may have harmful effects on the quality of the patient's survival. A full-Stokes laser-induced breakdown spectroscopy (FSLIBS) theory with a corresponding system is proposed to combine the elemental composition information and polarization information for glioma boundary detection. To verify the elemental content of brain tissues and provide an analytical basis, inductively coupled plasma mass spectrometry (ICP-MS) and LIBS are also applied to analyze the healthy, boundary, and glioma tissues. Totally, 42 fresh tissue samples are analyzed, and the Ca, Na, K elemental lines and CN, C2 molecular fragmental bands are proved to take an important role in the different tissue identification. The FSLIBS provides complete polarization information and elemental information than conventional LIBS elemental analysis. The Stokes parameter spectra can significantly reduce the under-fitting phenomenon of artificial intelligence identification models. Meanwhile, the FSLIBS spectral features within glioma samples are relatively more stable than boundary and healthy tissues. Other tissues may be affected obviously by individual differences in lesion positions and patients. In the future, the FSLIBS may be used for the precise identification of glioma boundaries based on polarization and elemental characterizing ability.

Porous Chitosan Composite Membrane Tandem Laser-Induced Breakdown Spectroscopy for Detection of Metal Elements in Liquid Samples

Laser-induced breakdown spectroscopy (LIBS) is currently one of the most popular techniques for direct element analysis of solid samples. However, when directly used for liquid sample analysis, there are disadvantages, including sample splashing, plasma quenching, and poor signal stability. These problems can be overcome through liquid-solid matrix conversion; at the same time, LIBS signal enhancement can be realized, and the sensitivity of detection of liquid samples can be improved. For this research, the authors used chitosan (CS) as a raw material, and introduced poly(vinyl alcohol) (PVA) and polyethyleneimine (PEI) to finally synthesize a new type of porous membrane material with better stability and more functional group content. The membrane was used as a liquid-solid conversion matrix material combined with LIBS technology to successfully achieve rapid separation and detection of Cu, Ag, Pb, and Cr, and the corresponding detection limits can reach 0.038, 0.069, 0.012, and 0.009 mg/L, respectively. This method further improves the sensitivity of the LIBS method. Combining it with membrane materials will replace inactive membranes and open up a new way for the rapid analysis of solution samples using LIBS technology.

Preliminary study of laser-induced breakdown spectroscopy for Mg/Ca investigation in cultured scallop shells

The element ratio of Mg/Ca is a primary proxy in studying the composition of seashells, and laser-induced breakdown spectroscopy (LIBS) is a practical technique for elemental analysis. In this work, we tried to apply LIBS to investigate the Mg/Ca ratio in cultured seashells of two scallop species (Chlamys farreri and Patinopecten yessoensis). It was found that LIBS was capable of tracking Mg/Ca variation on the cross section of the scallop shell (Chlamys farreri), and the variation trend was well verified by the measurement of SEM-EDS. Based on this, LIBS detection was carried out for Mg/Ca investigation on another species of the scallop shell (Patinopecten yessoensis), and the intensity ratio of Mg/Ca presented a similar variation to δ18O measurement under mass spectroscopy. The result also indicated that the LIBS technique is appropriate in the Mg/Ca investigation for scallop shells, and in cultured scallops, the Mg/Ca ratio would be equally useful for tracking temperature variations. In the future, LIBS is expected to be developed as a diagnostic tool in seashell cultivation, and more elemental compositions would be involved in this kind of investigation.

Chromium in soil detection using adaptive weighted normalization and linear weighted network framework for LIBS matrix effect reduction

Rapid and accurate detection of agricultural soil chromium (Cr) is of great significance for soil pollution assessment. Laser-induced breakdown spectroscopy (LIBS) could serve as a rapid and chemical-free method for hazardous metal analysis compared with conventional chemical methods. However, the detection of LIBS is interfered by uncertainty and matrix effect. In this study, an average strategy combined with linear weighted network (LWNet) was proposed to reduce the uncertainty. Adaptive weighted normalization-LWNet (AWN-LWNet) framework was proposed to reduce the matrix effect in two soil types. The results indicated that LWNet outperformed traditional machine learning and achieved the average relative error (ARE) of 2.08 % and 3.03 % for yellow brown soil and lateritic red soil, respectively. Moreover, LWNet could effectively mine Cr feature peaks even under the low spectral resolution. AWN-LWNet was the optimal model compared with commonly used models to reduce matrix effect (ARE=4.12 %). Besides, AWN-LWNet greatly reduced the number (from 22016 to 72) of spectral variables for model input. By extracting Cr peaks from models, the difference of Cr peaks intensity could be intuitively observed, which served as spectral interpretation for matrix effect reduction. The two methods have the potential to realize the detection of hazardous metals in soil by LIBS.

Improvement in detection reproducibility of laser-induced breakdown spectroscopy based on plasma acoustic correction

The LIBS acoustic correction (AC) method can effectively reduce the uncertainty of spectral signals and improve the robustness of calibration models and the long-term reproducibility of quantitative analysis.

Stable sensing platform for diagnosing electrolyte disturbance using laser-induced breakdown spectroscopy.

Electrolyte disturbance is very common and harmful, increasing the mortality of critical patients. Hence, rapid and accurate detection of electrolyte levels is vital in clinical practice. Laser-induced breakdown spectroscopy (LIBS) has the advantage of rapid and simultaneous detection of multiple elements, which meets the needs of clinical electrolyte detection. However, the cracking caused by serum drying and the effect of the coffee-ring led to the unstable spectral signal of LIBS and inaccurate detection results. Herein, we propose the ordered microarray silicon substrates (OMSS) obtained by laser microprocessing, to solve the disturbance caused by cracking and the coffee-ring effect in LIBS detection. Moreover, the area of OMSS is optimized to obtain the optimal LIBS detection effect; only a 10 uL serum sample is required. Compared with the silicon wafer substrates, the relative standard deviation (RSD) of the serum LIBS spectral reduces from above 80.00% to below 15.00% by the optimized OMSS, improving the spectral stability. Furthermore, the OMSS is combined with LIBS to form a sensing platform for electrolyte disturbance detection. A set of electrolyte disturbance simulation samples (80% of the ingredients are human serum) was prepared for this platform evaluation. Finally, the platform can achieve an accurate quantitative detection of Na and K elements (Na: RSD < 6.00%, R2 = 0.991; K: RSD < 4.00%, R2 = 0.981), and the detection time is within 5 min. The LIBS sensing platform has a good prospect in clinical electrolyte detection and other blood-related clinical diagnoses.

A Laser-Induced Breakdown Spectroscopy Experiment Platform for High-Degree Simulation of MarSCoDe In Situ Detection on Mars

The Zhurong rover of China’s Tianwen-1 mission started its inspection tour on Mars in May 2021. As a major scientific payload onboard the Zhurong rover, the Mars Surface Composition Detector (MarSCoDe) instrument adopts laser-induced breakdown spectroscopy (LIBS) to detect and analyze the chemical composition of Martian materials. This paper introduces an experimental platform capable of establishing a simulated Martian atmospheric environment, in which a duplicate model of the MarSCoDe flight model is placed. In the simulated environment, the limit vacuum degree can reach 10−5 Pa level, the temperature can change from −190 °C to +180 °C, and different gases can be filled and mixed according to desired proportion. Moreover, the sample stage can move along a track inside the vacuum chamber, enabling the detection distance to vary from 1.5 m to 7 m. Preliminary experimental results indicate that this platform is able to simulate the scenario of MarSCoDe in situ LIBS detection on Mars well.

Analysis of Metal Elements Contained in Graphite Target Coated With Chinese Medicinal Material Nanoparticles Using LIBS

A nanoparticle-coated graphite target (NCGT) is presented to improve the analysis accuracy and stability of laser-induced breakdown spectroscopy (LIBS). A stable, relatively homogeneous, and close to optically thin laser-induced breakdown plasma was obtained by dispersing sample nanoparticles on a high-purity graphite substrate. Spectral structures dominated by the characteristic lines of carbon and the samples can greatly simplify spectral identification and avoid line interference. To maximize the analysis accuracy and stability, a series of experimental conditions were optimized step by step according to the spectral intensity and signal-to-noise ratio of the lines. Based on the final optimized conditions, the relative standard deviation values of Mg, Fe, and Sr elemental content in Chinese medicinal material (CMM) samples were reduced from 17.7, 16.6, 12.1% of the pressed target to 4.8, 9.5, and 4.5% of the NCGT, respectively. Comparisons with the inductively coupled plasma mass spectrometry (ICP-MS) results demonstrated that the present method has great potential for detection of LIBS.

Spectral preprocessing to improve accuracy of quantitative detection of elemental Cr in austenitic stainless steel by laser-induced breakdown spectroscopy.

The production and consumption of austenitic stainless steel account for about 70% of stainless steel worldwide. The content of chromium (Cr) must be accurately detected and controlled to form a stable austenite structure and obtain strong properties in production. Laser-induced breakdown spectroscopy (LIBS) can be used to detect the Cr content of austenitic stainless steel in a complex production process. However, LIBS signals may be weak and unstable because the experimental signals are seriously affected by noise, self-absorption, the matrix effect, and the instability of the shot-to-shot signal, rendering the quantitative detection results inaccurate and unstable. The spectral-preprocessing methods of baseline correction and denoising can improve the accuracy of quantitative detection of LIBS. An improved segmented Hermite cubic-interpolation method is proposed herein to correct the baseline offset and produce baseline signals that are smooth and convergent (to overcome the Runge phenomenon). Empirical mode decomposition (EMD) based on the wavelet method is proposed to remove LIBS noise; this is done by exploiting the adaptivity of EMD to refine the wavelet-scaling coefficients. Compared with other denoising methods, the proposed method has good denoising evaluation indices and stability and, thus, effectively removes the noise. To verify detection accuracy, the internal standard quantitative method is used to detect the Cr content, and a cyclic-inversion prediction method is designed to verify detection stability. The results show that the correlation coefficient of the calibration curve is improved, the root-mean-square error is reduced, and the average relative error of the predicted Cr content decreases from 10.46% to 3.858%.

Quantitative analysis of trace elements (vanadium, sodium, and calcium) in petroleum coke using laser-induced breakdown spectroscopy with binder

The concentrations of Vanadium (V), Sodium (Na), and Calcium (Ca) have a great effect on the quality of petroleum coke. In this work, the trace elements of V, Na, and Ca in petroleum coke were determined by laser-induced breakdown spectroscopy (LIBS). First, petroleum coke powder was mixed with the stearic acid binder and pressed into pellets to achieve a high signal repeatability. Then, to optimize the percentage of the binder in the pressed pellets, the influence of stearic acid on LIBS signal was studied in detail. When the stearic accounted for 30 w% in the mixed-pressed pellets, the plasma morphology and spectral signal were more stable. Finally, the linear calibration curves were plotted by fitting the emission line intensities and the element concentrations. In addition, the results achieved through this method were compared with other conventional methods. The determination coefficients of calibration curves of V, Na, and Ca elements all exceed 0.99. The relative standard deviations of the predicted values of V, Na, and Ca concentrations were 3.65%, 4.38%, and 5.53%, respectively. We also calculated the limit of detection of the V, Na, and Ca elements, which were 1.19 mg/kg, 0.41 mg/kg, and 0.51 mg/kg, respectively. The experimental results demonstrate that LIBS detection is an accurate and precision method for the determination of trace elements in petroleum coke.

Quantitation improvement of underwater laser induced breakdown spectroscopy by using self-absorption correction based on plasma images

Laser-induced breakdown spectroscopy (LIBS) is a practical technique for in-situ detection, but self-absorption effect has been a big issue for quantitative applications of this technique. In presented work, a method was developed to correct self-absorption to improve the quantitation of underwater LIBS. We proposed “relative self-absorption coefficient” as the critical parameter to evaluate self-absorption, and the plasma image was employed as the reference to determine the coefficient value. Based on that, the LIBS detection was successfully corrected by the coefficient to realize quantitative analysis, and the “Dominant Factor-PLS” was used as assistance. The results indicated that our method greatly improved LIBS quantitation in practice. More importantly, the calibration curve was able to be established with high linearity (R2 = 0.9999) to cover a large concentration range (0–103 ppm). It is hoped that our method could be a contribution to developing LIBS as an analytical tool for field measurements.

Correction of moisture interference in laser-induced breakdown spectroscopy detection of coal by combining neural networks and random spectral attenuation

Increased humidity causes terrible accuracy in laser-induced breakdown spectroscopy analysis of coal. The moisture interference was reduced using artificial neural networks (ANN) combined with random spectral attenuation in this study.

Evaluation of electrosprayed graphene oxide coatings for elemental analysis by thin film microextraction followed by Laser-induced Breakdown Spectroscopy detection

In this work, a solid phase microextraction procedure, denoted as Thin Film Microextraction (TFME), was combined with Laser-induced Breakdown Spectroscopy for the detection of several analytes in aqueous solutions (Cu, Cr, Ni and Pb). The adsorbent films, consisting of a thin layer of graphene oxide deposited on glass substrates, were generated by using the electrospray deposition technique (ESD). Several parameters affecting the quality and shape of the films resulting from the ESD process were studied, and the morphology and adsorption capacity of the films were evaluated. The generated films were used for extraction of the target analytes from aqueous solutions and, after extraction, the analytes-enriched adsorbents were analysed by LIBS without the need of any desorption or elution step. In order to assess the analytical capability of the TFME-LIBS procedure, different analytical figures of merit of the proposed TFME-LIBS methodology were evaluated. The obtained limits of detection were 14 μg kg−1 for Pb and 15 μg kg−1 for the rest of the tested analytes. Measurement repeatability was better than 4% RSD at low concentration level (20 μg kg−1) but deteriorated by increasing the concentration level at 100 μg kg−1, with %RSD ranging from 3.6% (Cr) to 24% (Pb). Method trueness, evaluated from the analysis of a real sample of bottled water, led to recovery values in the range 85%–106%.

Improvement of laser induced breakdown spectroscopy signal using gas mixture

Laser induced breakdown spectroscopy (LIBS) is a spectral analysis technique characterized by the merits including rapidity, simple sample preparation, and spontaneous multi-element analysis, etc. In LIBS detection, the ambient gas plays an important role in interacting with the fast-expanding laser induced plasma (LIP) and greatly affects the LIBS signal. Therefore, it is important to investigate the effects of the ambient gas, especially the gas properties such as molecular weight, ionization energy, and thermal capacity, etc. on LIBS signals to better understand the interactions between the surrounding gas and the LIP, and improve the signal quality of LIBS. However, it is very hard to change only one property of the ambient gas while keeping the others unchanged because of the unavailability of such gases, thus in this study, a series of gas mixtures composed of He, Ne and Ar were utilized to obtain diverse properties necessary for the investigation, while titanium alloy is used as a sample. Results revealed that for some gas mixtures (such as 40% He, 40% Ne, and 20% Ar gas mixture), signal intensities were enhanced and relative standard deviation (RSD) values were significantly decreased. The plasma temperature T, electron density ne, and total number density ns were also calculated to analyze the mechanism of gas effect on LIBS signals. Results showed that the change of the gas species mainly has influences on the total number density ns, and further leads to the change of signals intensities and RSDs. The relation between some gas properties and LIBS signal was then discussed and the mechanism of some leading properties, such as the molecular weight, ionization energy, thermal conductivity, and viscosity were analyzed to explain how these properties work on LIBS signals.

Detecting sulfur on the Moon: The potential of vacuum ultraviolet laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) receives increasing interest in the field of space exploration. Some volatile elements important to planetary research are, however, challenging to detect with conventional LIBS because their strongest emission lines lie in the vacuum-UV (VUV) spectral range below 200nm. We demonstrate the potential of LIBS detection in the VUV range from 125 to 190nm on one of the relevant challenging elements, sulfur (S), in a lunar context. With our laboratory set-up, we detected S in lunar analogues at concentrations ranging from 0.5 to 4.0at% in a time-integrated configuration. The experiments were conducted in high vacuum (10−3 Pa) with laser parameters realistic for a space instrument (1064nm, 25mJ, 6ns). The results indicate improved detection capabilities for S in a lunar geological context as compared to LIBS in the more common UV/VIS/NIR spectral range. We found limits of detection in the order of 0.5at% S for all investigated sample series. Normalization by total intensity and by an internal standard, in our case by the emission signal of the O I triplet at 130nm, was tested as well, but did not yield a noticeable improvement for our data. Besides S, we were also able to detect Al, Fe, O, Si and Ti from the lunar analogue matrix.

A low-cost LIBS detection system combined with chemometrics for rapid identification of plastic waste

We present, rapid and efficient identification of ten different types of post-consumer plastics obtained from a local recycling unit by deploying a low cost, compact CCD spectrometer in laser-induced breakdown spectroscopy (LIBS) technique. For this investigation, spectral emissions were collected by an Echelle spectrograph equipped with an intensified charge-coupled device (ES-ICCD) as well as a non-gated Czerny Turner CCD spectrometer (NCT-CCD). The performance is evaluated by interrogating the samples in a single-shot as well as accumulation mode (ten consecutive laser shots). The results from principal component analysis (PCA) have shown excellent discrimination. Further, the artificial neural network (ANN) analysis has demonstrated that individual identification accuracies/rates up to ~99 % can be achieved. The data acquired with ES-ICCD in the accumulation of ten shots have shown average identification accuracies ~97 %. Nevertheless, similar performance is achieved with the NCT-CCD spectrometer even in a single shot acquisition which reduces the overall analysis time by a factor of ~15 times compared to the ES-ICCD. Furthermore, the detector/collection system size, weight, and cost also can be reduced by ~10 times by employing a NCT-CCD spectrometer. The results have the potential in realizing a compact and low-cost LIBS system for the rapid identification of plastics with higher accuracies for the real-time application.