On-stream analysis of iron ore slurry using laser-induced breakdown spectroscopy

XRF online analyzer for measurements of P2O5 content in phosphate slurry

Online X-ray Fluorescence (XRF) setup was constructed and optimized for analysing the P2O5 content in phosphate slurry (PS). Serval samples were analysed using two configurations of the setup, one with low and vertical flow and another with high and horizontal flow. The mean absolute error achieved through the first configuration was 0.87% and 0.38% using the second configuration. Reference samples were analyzed using the two configurations to construct the calibration curves. The curves cover a concentration range of P2O5 from 13.50 to 18.50% when considering the horizontal flow configuration, and a range of 14.00-15.60% when considering the vertical flow setup. An experimental study was conducted in order to optimize the measurement parameters for the online measurement of P2O5 in the phosphate slurry using the horizontal flow setup. A good signal-to-noise ratio (SNR) of [Formula: see text] was attained using an excitation energy of 20 kV or 25 kV, an excitation current of 600 µA, a distance of 18 mm between the sample and the detector, a measurement time of 60 s per spectrum and the use of an Aluminum filter between the X-ray tube and the measurement window. Online X-ray fluorescence analysis of P entails some challenges due to the low characteristic energy of P, the phosphate slurry matrix and the online analysis mode. However, the outcomes of this study indicate that XRF is a promising technology to meet the requirement for digitalization of chemical analysis of phosphate products.

Sensitive Detection of the Human Epididymis Protein-4 (HE4) Ovarian Cancer Biomarker through a Sandwich-Type Immunoassay Method with Laser-Induced Breakdown Spectroscopy

Detection of cancer before the appearance of any symptoms is crucial for successful treatment. Early detection is, however, very challenging, particularly for the types of cancer with few or no symptoms at early stages, such as epithelial ovarian cancer (EOC). Developing a user-friendly method that can detect biomarkers with sufficient selectivity, sensitivity, and reproducibility is a promising approach for overcoming the challenges of early detection of EOC. In this study, we report a sandwich-type microparticle immunoassay for sensitive detection of the HE4 biomarker with laser-induced breakdown spectroscopy. Here, we cross-linked elemental particles to a specific functional group of the targeted biomolecules based on a covalent and non-covalent linking chemistry to improve the sensitivity and selectivity of biomarker detection, in which Fe₃O₄ and SiO₂ microparticles were used to conjugate and purify the antibody-antigen in complex media. Simultaneous detection of Fe and Si from a magnetically purified assay significantly improves the HE4 biomarker's detectability, in which HE4 was detected with a limit of detection of 0.0022 pM. We also determined the coupling ratio between HE4 and silica particles using a silicon calibration curve.

Efficient weakly supervised LIBS feature selection method in quantitative analysis of iron ore slurry

On-stream analysis of the element content in ore slurry plays an important role in the control of the mineral flotation process. Therefore, our laboratory developed a LIBS-based slurry analyzer named LIBSlurry, which can monitor the iron content in slurries in real time. However, achieving high-precision quantitative analysis results of the slurries is challenging. In this paper, a weakly supervised feature selection method named spectral distance variable selection was proposed for the raw spectral data. This method utilizes the prior information that multiple spectra of the same slurry sample have the same reference concentration to assess the important weight of spectral features, and features selected by this prior can avoid over-fitting compared with a traditional wrapper method. The spectral data were collected on-stream of iron ore concentrate slurry samples during the mineral flotation process. The results show that the prediction accuracy is greatly improved compared with the full-spectrum input and other feature selection methods; the root mean square error of the prediction of iron content can be decreased to 0.75%, which helps to realize the successful application of the analyzer.

Handheld LIBS for Li Exploration: An Example from the Carolina Tin-Spodumene Belt, USA

Laser-induced breakdown spectroscopy (LIBS), which has recently emerged as tool for geochemical analysis outside the traditional laboratory setting, is an ideal tool for Li exploration because it is the only technique that can measure Li in minerals, rocks, soils, and brines in-situ in the field. In addition to being used in many products essential to modern life, Li is a necessary element for a reduced carbon future and Li–Cs–Ta (LCT) granitic pegmatites are an important source of Li. Such pegmatites can have varying degrees of enrichment in Li, Rb, Cs, Be, Sn, Ga, Ta>Nb, B, P, and F. We focus here on the LCT pegmatites of the Carolina Tin-Spodumene Belt (CTSB) situated in the Kings Mountain Shear Zone, which extends from South Carolina into North Carolina. The CTSB hosts both barren and fertile pegmatites, with Li-enriched pegmatites containing spodumene, K-feldspar, albite, quartz, muscovite, and beryl. We illustrate how handheld LIBS analysis can be used for real-time Li analysis in the field at a historically important CTSB pegmatite locality in Gaston County, N.C. in four contexts: (i) elemental detection and identification; (ii) microchemical mapping; (iii) depth profiling; and (iv) elemental quantitative analysis. Finally, as an example of a practical exploration application, we describe how handheld LIBS can be used to measure K/Rb ratios and Li contents of muscovite and rapidly determine the degree of pegmatite fractionation. This study demonstrates the potential of handheld LIBS to drastically reduce the time necessary to acquire geochemical data relevant to acquiring compositional information for pegmatites during a Li pegmatite exploration program.

Meat species identification accuracy improvement using sample set portioning based on joint x-y distance and laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was suitable for the identification of meat species due to fast and less sample preparation. However, the problem of low accuracy rate of the recognition model caused by improper selection of training set samples by random split has severely restricted the development of LIBS in meat detection. Sample set portioning based on the joint x-y distance (SPXY) method was applied for dividing the meat spectra into a training set and a test set. Then, the five kinds of meat samples (shrimp, chicken, beef, scallop, and pig liver) were classified by the support vector machine (SVM). With the random split method, Kennard-Stone method, and SPXY method, the recognition accuracies of the SVM model were 90.44%, 91.95%, and 94.35%, respectively. The multidimensional scaling method was used to visualize the results of the sample split for the interpretation of the classification. The results showed that the identification performance of the SPXY method combined with the SVM model was best, and the accuracy rates of shrimp, chicken, beef, scallop, and pig liver were 100.00%, 100.00%, 100.00%, 78.57%, and 92.00%, respectively. Moreover, to verify the broad adaptability of the SPXY method, the linear discriminant analysis model, the K-nearest neighbor model, and the ensemble learning model were applied as the meat species identification model. The results demonstrated that the accuracy rate of the classification model can be improved with the SPXY method. In light of the findings, the proposed sample portioning method can improve the accuracy rate of the recognition model using LIBS.

On-line quantitative analysis of heavy metals in water based on laser-induced breakdown spectroscopy

Heavy metal pollution from industrial wastewater is an important source. A method for heavy metals determination in industrial wastewater based on laser-induced breakdown spectroscopy (LIBS) technique was studied and the on-line monitoring system that used automatic graphite enrichment and spatial plasma confinement detection was developed and field demonstrated. The limits of detection (LOD) of heavy metal elements (Cd, Cr, Cu, Ni, Pb, Zn) could reach several μg/L. In Tongling, the on-line heavy metal monitor was field demonstrated. The calibration curves of copper and zinc were built on site, and then on-line monitoring was conducted. The measurement results of this monitor were compared with ICP-OES and had a good correlation. The results showed that the heavy metal monitor could be used for on-line detection of heavy metals in wastewater and had a good reliability.

Accuracy improvement of quantitative analysis in spatially resolved fiber-optic laser-induced breakdown spectroscopy

Fiber-optic laser-induced breakdown spectroscopy (FO-LIBS) has been employed in many applications because of the flexibility of optical fiber cable. However, the inhomogeneous elemental distribution of plasmas can cause a self-absorption effect and, hence, significantly hinder the determination of FO-LIBS. Here, to solve this flaw, we took iron (Fe), magnesium (Mg), and zinc (Zn) elements in aluminum alloy as examples to investigate the self-absorption reduction and accuracy improvement using spatially resolved FO-LIBS. Spatially resolved FO-LIBS means the spectra were collected at different positions along the direction parallel to the surface of the sample rather than at the center of the plasma. With this method, the self-absorption effect could be improved by selecting different acquisition positions along the X-axis. The root mean square error of cross-validations (RMSECV) for Fe, Mg, and Zn were reduced from 0.388, 0.348, and 0.097 wt. % to 0.172, 0.224, and 0.024 wt. %, respectively. Generally, spatial resolution is an effective method of self-absorption reduction and accuracy improvement in FO-LIBS.

Spreading a water droplet through filter paper on the metal substrate for surface-enhanced laser-induced breakdown spectroscopy

To improve the quantitative analysis accuracy of an aqueous solution using surface-enhanced laser-induced breakdown spectroscopy (SENLIBS), the filter paper was used as a transmission medium by placing it onto the surface of a metallic substrate to make the microdroplet spreading more uniform in a fixed region of the substrate surface. The trace elements (Cu, Pb, Cd, and Cr) in an aqueous solution were detected successfully using this method. The results showed that the sample preparation repeatability of SENLIBS was noticeably improved with the aid of filter paper. Moreover, the limit of detection (LoD) values was similar to those without filter paper. Furthermore, the R² values were improved from 0.6192~0.9321 to 0.9481~0.9766, the RMSECV values were decreased from 0.53~1.95 μg/mL to 0.33~1.06 μg/mL, and the average relative error (ARE) values were decreased from 8.96~22.31% to 4.28~14.37% with the aid of filter paper. This demonstrated that the use of filter paper could improve the quantitative analysis accuracy of SENLIBS by increasing the sample preparation repeatability.

One-point and multi-line calibration method in laser-induced breakdown spectroscopy

The calibration-free laser-induced breakdown spectroscopy (CF-LIBS) and its variations are low cost, short time consumption, and high adaptability. However, seeking a more flexible and simple quantitative analysis method remains a challenge. A one-point and multi-line calibration (OP-MLC) was presented as a simple quantitative analysis method of LIBS. The results showed that OP-MLC-LIBS method can achieve quantitative analysis using only one standard sample, and the average relative errors (AREs) are 9, 22, 21 and 36% for Mn, Cr, Ni and Ti elements in six tested low-alloy steel samples, respectively. The method requires neither a large number of standard samples nor complicated calculations, which provides a flexible and low-cost quantitative analysis approach for development and application of LIBS.

Determination of potassium in ceramic raw materials using laser-induced breakdown spectroscopy combined with profile fitting

The determination of potassium (K) content in ceramic raw materials provides important references for ceramic sintering. To realize rapid, in situ, and real-time analysis detection, a laser-induced breakdown spectroscopy (LIBS) system was set up to analyze K content in ceramic raw materials. However, the self-absorption was the serious influence on the accuracy of K element analysis. In this work, a method of profile fitting with Lorentz function was proposed to reduce the self-absorption effect in LIBS. After Lorentz fitting, the determination coefficient (R² factor) for K element improved from 0.993 to 0.998, the root mean square error of cross-validation reduced from 0.458 wt. % to 0.145 wt. %, and the average relative error reduced from 13.769% to 5.121%. The results indicate that the Lorentz fitting can effectively reduce the self-absorption effect, and improve the accuracy of quantitative analysis for K element. According to the results, the proposed approach can be a promising method for determination of elements that suffer from self-absorption in LIBS.

Simple method for liquid analysis by laser-induced breakdown spectroscopy (LIBS)

As a fast-developing technique for in situ multi-element analysis method, laser induced breakdown spectroscopy - LIBS is, however, developing slowly on liquid analysis due to some technical difficulties. We propose a new method, namely capillary mode, to quantify the concentrations of the elements in solution using LIBS. A Nd:YAG laser with repetition of 10 Hz were used to analyze the solution of Na₂CrO₄ and no any sample preparation in measurements. The experimental results show that the splashing of liquid induced by laser pulses is decreased significantly and the pollution of mirrors is avoided effectively using liquid capillary mode. The results of quantitative analysis for liquid are also improved than other method. The calibration curves of Cr and Na are well characterized by straight lines and the regression coefficient values of the linear fit are better than 0.998. The limits of detection (LODs) of Cr and Na are determined to be 28.9 mg/L and 1.0 mg/L in this work, respectively. The experimental results show that the liquid capillary mode provides a more practical and very simple approach to improve accuracy of quantitative element analysis in liquids by LIBS technique.

Accuracy and stability improvement for meat species identification using multiplicative scatter correction and laser-induced breakdown spectroscopy

An efficient method has been developed to identify meat species by using laser-induced breakdown spectroscopy (LIBS). To improve the accuracy and stability of meat species identification, multiplicative scatter correction (MSC) was adopted to first pretreat the spectrum for correction of spectrum scatter. Then the corrected spectra were identified by using the K-nearest neighbor (KNN) model. The results showed that the identification rate improved from 94.17% to 100% and the prediction coefficient of variance (CV) decreased from 5.16% to 0.56%. This means that the accuracy and stability of meat species identification using MSC and LIBS simultaneously improved. In light of the findings, the proposed method can be a valuable tool for meat species identification using LIBS.