Fast quantitative determination of platinum in liquid samples by laser-induced breakdown spectroscopy

Detection of Low Lithium Concentrations Using Laser-Induced Breakdown Spectroscopy (LIBS) in High-Pressure and High-Flow Conditions

This paper describes the effects of laser pulse rate and solution flow rate on the determination of lithium at high pressure for water and 2.5% sodium chloride solutions using laser-induced breakdown spectroscopy (LIBS). Preliminary studies were performed with 0-40 mg L^-1 Li solutions, at ambient pressure and at 210 bar, and in static and flowing (6 mL · min^-1) regimes, for a combination of four different measurement conditions. The sensitivity of calibration curves depended on the pressure and the flow rate, as well as the laser pulse rate. The sensitivity of the calibration curve increased about 10% and 18% when the pressure was changed from 1 to 210 bar for static and flowing conditions, respectively. However, an effect of flow rate at high pressure for both 2 and 10 Hz laser pulse rates was observed. At ambient pressure, the effect of flow rate was negligible, as the sensitivity of the calibration curve decreased around 2%, while at high pressure the sensitivity increased around 4% when measurements were performed in a flow regime. Therefore, it seems there is a synergistic effect between pressure and flow rate, as the sensitivity increases significantly when both changes are considered. When the pulse rate is changed from 2 to 10 Hz, the sensitivity increases 26-31%, depending on the pressure and flow conditions. For lithium detection limit studies, performed with a laser pulse energy of 2.5 mJ, repetition rate of 10 Hz, gate delay of 500 ns, gate width of 1000 ns, and 1000 accumulations, a value around 40 µg L^-1 was achieved for Li solutions in pure water for all four measurement conditions, while a detection limit of about 92 µg L^-1 was determined for Li in 2.5% sodium chloride solutions, when high pressure and flowing conditions were employed. The results obtained in the present work demonstrate that LIBS is a powerful tool for the determination of Li in deep ocean conditions such as those found around hydrothermal vent systems.

Laser-Induced Breakdown Spectroscopy (LIBS) Measurement of Uranium in Molten Salt

In this current study, the molten salt aerosol-laser-induced breakdown spectroscopy (LIBS) system was used to measure the uranium (U) content in a ternary UCl₃-LiCl-KCl salt to investigate and assess a near real-time analytical approach for material safeguards and accountability. Experiments were conducted using five different U concentrations to determine the analytical figures of merit for the system with respect to U. In the analysis, three U lines were used to develop univariate calibration curves at the 367.01 nm, 385.96 nm, and 387.10 nm lines. The 367.01 nm line had the lowest limit of detection (LOD) of 0.065 wt% U. The 385.96 nm line had the best root mean square error of cross-validation (RMSECV) of 0.20 wt% U. In addition to the univariate calibration approach, a multivariate partial least squares (PLS) model was developed to further analyze the data. Using partial least squares (PLS) modeling, an RMSECV of 0.085 wt% U was determined. The RMSECV from the multivariate approach was significantly better than the univariate case and the PLS model is recommended for future LIBS analysis. Overall, the aerosol-LIBS system performed well in monitoring the U concentration and it is expected that the system could be used to quantitatively determine the U compositions within the normal operational concentrations of U in pyroprocessing molten salts.

An Image Auxiliary Method for Quantitative Analysis of Laser-Induced Breakdown Spectroscopy

Improving both the stability and accuracy of laser-induced breakdown spectroscopy (LIBS) is an issue in quantitative analysis. For certain environments outside of the laboratory, consistently and exactly maintaining the distance from the optical system to the sample surface is difficult, and fluctuations of this distance severely affect the stability of the spectrum. In this work, the principal components of the plasma images are extracted and used to correct the spectral line intensities as an auxiliary method to reduce spectral fluctuation. The presented image auxiliary method is combined with univariate analysis and multivariate analysis, and the element concentrations of Cu, Mn, V, and Cr in steel samples are analyzed. For univariate analysis, all the determination coefficients ( R²) of the four elements exceed 0.99, whereas the average relative standard deviations (RSDs) of the intensities decrease from 30.45, 23.14, 27.03, and 22.04%, to 2.13, 3.38, 2.49, and 3.58%, respectively. For the multivariate analysis, the R² values for Cu, Mn, V, and Cr also all exceed 0.99, and the average RSDs of the predicted concentrations of the validation samples decrease to 2.87, 3.82, 2.86, and 6.51%, respectively.

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

On-stream analysis of the element content in ore slurry has important significance in the control of the flotation process and full use of raw materials. Therefore, techniques that can monitor the chemistry in slurries online are required. Laser-induced breakdown spectroscopy (LIBS) is one of the potential approaches to online measurements due to its capability of in situ and real-time analysis. However, using LIBS for on-stream analysis of slurries is challenging due to the issues such as surface ripples, sample splashing, sedimentation, etc. To address these problems, we developed a slurry circulation system. The effects of slurry flow rate on LIBS spectra were investigated to achieve the optimal detecting surface for better repeatability of LIBS. The coefficient of determination R² of the calibration curve for Fe element is 0.982, and the limit of detection of Fe element was estimated to be 0.075 wt. % under the optimized experimental parameters. The results show that this slurry circulation system is applicable to the on-stream slurry analysis.

Elemental Detection of Cerium and Gadolinium in Aqueous Aerosol via Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was used to detect and measure the concentrations of Ce and Gd in aqueous aerosol solutions. A total of 36 standards, with concentrations of Ce and Gd ranging from 100 parts per million (ppm) to 10 000 ppm, were made to explore the relationship between them. In this study, a Collison nebulizer with an argon carrier gas was used to generate the aerosol droplets. For each liquid sample, ten repetitions of 200 laser shots each were recorded. The percent relative standard deviations (%RSD) were on an average of 7.5% between the ten different sample repetitions. Due to the close proximity of the Ce and Gd lines, it was challenging to identify peaks with low interferences. However, several lines were identified, calibration curves were constructed, and the best curves were generated using the 457.228 nm line for Ce and the 409.861 nm line for Gd. The LODs for these curves were calculated to be 209.7 ppm and 216.4 ppm for the Ce line and Gd line, respectively.

Laser-induced breakdown spectroscopy of liquid solutions: a comparative study on the forms of liquid surface and liquid aerosol

Liquid surface and liquid aerosol as the traditional liquid forms for laser-induced breakdown spectroscopy (LIBS) and inductively coupled plasma (ICP), respectively, have been used to analyze chromium (Cr) and cadmium (Cd) elements using LIBS in a liquid solution. The spectral differences, the effects of laser energy and laser frequency, the accumulated number of laser pulses, gate delay time, and the quantitative analyses for a liquid surface and a liquid aerosol were compared. The results showed that the liquid surface demonstrated a lower plasma threshold, higher optical emission intensity, and higher single-to-noise ratio. Moreover, the relative standard deviations (RSDs) of the intensities of the liquid aerosol are better than those of the liquid surface. Furthermore, the results of the quantitative analyses of Cr I 357.86 nm and Cd I 361.05 nm of the liquid surface are close to those of the liquid aerosol. The limit of detections of Cr and Cd of the liquid surface were 2.764 and 86.869  μg/mL, which were close to those of liquid aerosol, 2.847  μg/mL of Cr and 97.635  μg/mL of Cd. For both the liquid surface and liquid aerosol, the coefficient of determination R² of the calibration curve for Cr and Cd were above 0.99, and the average RSDs of Cr and Cd of the liquid surface were 0.027 and 0.054, which were similar to the 0.020 of Cr and 0.042 of Cd of the liquid aerosol. These results suggest that both the liquid surface and aerosol have similar detection abilities for water quality monitoring.

Emission enhancement of laser-induced breakdown spectroscopy for aqueous sample analysis based on Au nanoparticles and solid-phase substrate

In this paper, porous electrospun ultrafine fiber with a nanoparticle coating was proposed as an effective approach to enhance the laser-induced breakdown spectroscopy (LIBS) signal for metal ions in aqueous systems. It is known that the LIBS technique is very limited when used for liquid sample analysis. On the other hand, in practical applications, many LIBS measurements have been accomplished in a liquid environment. A signal enhancement method for aqueous sample LIBS analysis was presented in this work, where Au nanoparticles and a solid-phase support were combined for the first time for aqueous sample analysis with LIBS. The system operation was relatively simple, which only required Au nanoparticles being dropped onto the surface of porous electrospun ultrafine fibers before LIBS analysis. Significant signal enhancement was achieved due to the integration of the merits of the Au nanoparticles and the ultrafine fibers. Nanoparticles possess significant LIBS signal enhancement effects by providing several plasma ignition points and then causing more efficient emissions. In addition, Au nanoparticles could also help to decrease the breakdown threshold of target elements for LIBS analysis. The electrospun ultrafine fibers as solid-phase support can accommodate a larger volume of aqueous sample. Meanwhile, the aqueous solution on the fiber surface was easy to evaporate. The experimental results showed that the limits of detection (LODs) with this method were significantly improved, 0.5 μg/mL for Cr, 0.5 μg/mL for Pb, and 1.1 μg/mL for Cu, respectively, compared with 2.0 μg/mL for Cr and 3.3 μg/mL for Cu in the previous research. In the proposed method, signal enhancement could be achieved without any extra equipment, which makes the LIBS technique feasible for direct measurement of an aqueous sample.

Quantitative detection of metallic traces in water-based liquids by microwave-assisted laser-induced breakdown spectroscopy

The enhancement of laser-induced breakdown spectroscopy (LIBS) assisted with microwave radiation is demonstrated for an aqueous solution of indium using the 451.13 nm emission line. Microwave power was delivered via a near-field applicator to the LIBS measurement volume where the indium aqueous solution was presented as a liquid jet. The microwave enhancement effect was observed to decrease with increasing laser pulse fluence at 532 nm resulting in a maximum emission intensity occurring at a laser pulse fluence of 85.2 J∙cm(-2), independent of the microwave power used. The detection limits of indium in an aqueous solution were determined to be 10.8 ± 0.7 and 124 ± 5 ppm for the cases of microwave enhanced and standard LIBS, respectively. The 11.5-fold detection limit enhancement obtained in the liquid phase is of the same order of magnitude as that reported for other elements in solid samples, but lower than that obtained in solid phase utilizing a similar experimental setup. This establishes microwave enhancement as an effective technique for the detection of metals in aqueous solutions. In addition, the temporal evolution of plasma emission intensity was investigated and was found to be qualitatively similar to that of plasma produced from solid phase samples, which reveals the same coupling mechanism between laser generated plasma and microwave radiation.