Dehydrated Carbon Coupled with Laser-Induced Breakdown Spectrometry (LIBS) for the Determination of Heavy Metals in Solutions

Agarose Film-Based Liquid–Solid Conversion for Heavy Metal Detection of Water Samples by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) shows promising applications in the analysis of environmental heavy metals. However, direct analysis in water by LIBS faces the problems of droplet splashing and laser energy decay. In this study, a novel liquid–solid conversion method based on agarose films is proposed to provide an easy-to-operate and sensitive detection of heavy metals. First, the water samples were converted into semi-solid hydrogels with the aid of agarose and then dried into agarose films to make the signal intensities stronger. The calibration curves of Cd, Pb and Cr were constructed. The proposed method was validated by standard heavy metal solutions and real water samples. The results showed that the values of R2 were 0.990, 0.989 and 0.975, and the values of the LOD were 0.011, 0.122 and 0.118 mg L−1 for Cd (I) 228.80, Pb (I) 405.78 and Cr (I) 427.48 nm, respectively. The RMSEs of validation were 0.068 (Cd), 0.107 (Pb) and 0.112 mg·L−1 (Cr), and the recovery values were in the range of 91.2–107.9%. The agarose film-based liquid–solid conversion method achieved the desired ease of operation and sensitivity of LIBS in heavy-metal detection, thereby, showing good application prospects in heavy metal monitoring of water.

Ultrasensitive and Simultaneous Detection of Multielements in Aqueous Samples Based on Biomimetic Array Combined with Laser-Induced Breakdown Spectroscopy

Ultrasensitive detection of metallic elements in liquids has attracted considerable attention in fields such as environmental pollution monitoring and drinking water quality control. Hence, it is of great significance to develop a sensitive and simultaneous detection strategy for multiple metal elements in liquid. Laser-induced breakdown spectroscopy (LIBS) technology shows unique advantages because of its simple, rapid, and real-time in situ detection, but the laser energy will be greatly attenuated in the liquids; thus, the sensitivity of LIBS for direct detection of metal elements in liquid samples will decrease sharply. In this study, inspired by the structure of Stenocara beetle's back, a superhydrophobic biomimetic interface with hydrophilic array was prepared for enriching low-concentration targets into detection regions, and the biomimetic array LIBS (BA-LIBS) was successfully established. The ultrasensitive and simultaneous detection of nine metal elements in drinking water was realized based on the effective enrichment method. The limits of detection of the nine metal elements in mixed solution ranged from 8.3 ppt to 13.49 ppb. With these excellent properties, this facile and ultrasensitive BA-LIBS strategy might provide a new idea for the prevention and control of metal hazards in the liquid environment.

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.

Analytical-performance improvement of aqueous solution by chemical replacement combined with surface-enhanced laser-induced breakdown spectroscopy

In this study, chemical replacement combined with surface-enhanced laser-induced breakdown spectroscopy (CR-SENLIBS) was introduced for detecting the trace chromium (Cr) element in an aqueous solution, which could use chemical replacement to change the sample from liquid to solid. In order to illustrate the analytical-performance of the CR-SENLIBS, the direct analysis of the liquid surface by LIBS (LSLIBS) was investigated for comparison. The results show that the spectral intensity of Cr I 357.86 nm, plasma lifetime, and spectral stability were improved. Moreover, the limit of detection of Cr I 357.86 nm was 0.018 μg/mL, which was lower than 1.814 μg/mL for LSLIBS. Furthermore, the accuracy and precision were improved more than 60% and 80%, respectively; for example, the root-mean-square error of cross-validation was improved from 1.09 to 0.75 μg/mL, and the average relative standard deviation of the predicted concentration of Cr was reduced from 22.89% to 4.53% by using CR-SENLIBS. These results suggest that CR-SENLIBS has good analytical-performance, which exhibits great potential in water quality monitoring.

Highly concentrated, ring-shaped phase conversion laser-induced breakdown spectroscopy technology for liquid sample analysis

A highly concentrated, ring-shaped phase conversion (RSPC) method was developed for liquid sample analysis using the laser-induced breakdown spectroscopy (LIBS) technique. In this work, test samples were prepared by mixing the metal particles with polyvinyl alcohol (PVA) supporter in liquid phase. With heat, the PVA solution solidified inside a modified glass petri dish, forming a metal-enriched polymer ring film. Distinguished from other traditional liquid-to-solid conversing methods, the proposed new method takes advantage of enhanced homogeneity for the target elements inside the ring film. The modified glass petri dish was used to control the ring-shaped concentration. Due to the specially designed circular groove at the bottom of this dish, where the PVA solution and liquid sample mixture accumulated, the target elements were concentrated in this small ring, which is beneficial for enhancing and stabilizing the plasma signals compared to the direct liquid sample analysis using LIBS. The limits of detection for Ag, Cu, Cr, and Ba obtained with the RSPC-LIBS technology were 0.098  μg·mL^-1, 0.18  μg·mL^-1, 0.83  μg·mL^-1, and 0.046  μg·mL^-1, respectively, which provided greater improvement than the direct bulk liquid analysis using LIBS.