Laser induced breakdown spectroscopy (LIBS); On-line analysis; Heavy metal; Enrichment; Instrument system;QUANTITATIVE-ANALYSIS; LIBS; CADMIUM; SAMPLES; LEAD

The enrichment method of heavy metal in water with graphite and aluminum electrode was studied, and combined with plasma restraint device for improving the sensitivity of detection and reducing the limit of detection (LOD) of elements. For aluminum electrode enrichment, the LODs of Cd, Pb and Ni can be as low as several ppb. For graphite enrichment, the measurement time can be less than 3 min. The results showed that the graphite enrichment and aluminum electrode enrichment method can effectively improve the LIBS detection ability. The graphite enrichment method combined with plasma spatial confinement is more suitable for on-line monitoring of industrial waste water, the aluminum electrode enrichment method can be used for trace heavy metal detection in water. A LIBS method and device for soil heavy metals analysis was also developed, and a mobile LIBS system was tested in outfield. The measurement results deduced from LIES and ICP-MS had a good consistency. The results provided an important application support for rapid and on-site monitoring of heavy metals in soil. (C) 2017 Elsevier B.V. All rights reserved.

Laser-induced breakdown spectroscopy; Quantitative analysis; Standard addition method; Curve fitting; Heavy metals;

Quantitative analysis of four heavy metals Pb, Cr, Cu and Cd in soils and solid wastes using independently developed portable system of laser-inducedbreakdown spectroscopy. A Nd: YAG pulse laser with fundamental wavelength of 1 064 nm is used as the excitation source, with the single pulse energy of 100 mJ the pulse width of 6 ns, and the operating frequency 3 Hz. The echelle spectroscopy with high resolution and wide spectral range is used as the spectral separation device, and the intensified charge coupled device GOOD) as the spectral detection device in the experiment, with the detection range of 200 similar to 500 nm and a resolution of 0.08 similar to 0.12 nm. In order to improve the spectral intensity and detection sensitivity, a device of hemisphere spatially bound is used to restrain the plasma and a optical fiber with multi-channel is used collect the signal. The reception angle is 45 degrees. The laserrepetition rate is 2 Hz while the delay is 1.5 mu s, with the gate width of 1.05 ms. Standard addition method is used to effectively solve the quantitative analysis of samples of unknown matrix. The innovation lies in the fact that, a curve fit instead of a straight line fit is used in the standard addition method to quantitative analyze the heavy metals in soils and solid wastes, which effectively improve the measurement results. Especially for the low concentrations of soil samples, linear fitting can not be used in quantitative analysis, in contrast, the correlation coefficient of curve fitting is much higher, more closer to the national standard measurement methods, to meet soil pollution detection. The result of seven soils and solid wastes samples are as follows, line fitting relative error: Pb 1.26%similar to 79.38%, Cr-22. 44%similar to 82.06%, Cu 15.09%similar to 190.50%, Cd 32.76%similar to 167.96%, and curve fitting relative error respectively Pb - 4.19%similar to 11.92%, Cr-38.31%similar to 9.26%, Cu-7.24% similar to 26.86%, Cd-10.52%similar to 12.94%, the average relative error is 10.47%.

LIBS; POLLUTION; CHINA

In this work, a mobile laser-induced breakdown spectroscopy (LIBS) system has been successfully applied to in situ analysis of heavy metals in soil samples. The LIBS system had two working methods, which were a fixed measuring method and a handheld method. For the fixed measuring method, a simple sample pretreatment was needed to reduce the soilmatrix effect generated by moisture and porosity. Experiments proved that this method could be used to semi-quantitatively detect heavy metals when combined with the traditional calibration curve method. The limits of detection for copper, lead, and zinc were all below 10 mg/kg, which satisfied the need of heavy metal detection in soil. Principal component analysis was used for soil classification, which helped to build appropriate calibration curves. On the basis of soil classification, accurate and rapid detection of heavy metals in soil is feasible. For the handheld method, spectrum intensity and stability decreased significantly compared with the fixed measuring method. However, by using the internal standard method, the stability of LIBS data was improved significantly to 6%. For soil samples with serious heavy-metal pollution, the measurement errors were less than 12%, which indicated that handheld LIBS was effective to monitor heavy-metal pollution in soil. The research results provide application support for rapid and on-site monitoring of heavy metals in soil. (C) 2017 Optical Society of America

INDUCTIVELY-COUPLED PLASMA; ATOMIC-ABSORPTION-SPECTROMETRY; COMPOSITE FILM ELECTRODES; RAY-FLUORESCENCE ANALYSIS; HEXAVALENT CHROMIUM; WASTE-WATER; ELECTROCHEMICAL DETECTION; MATRIX CONVERSION; OXIDE COMPOSITES; METAL DETECTION

Traditional laser-induced breakdown spectroscopy (LIES) always fails to directly detect target in aqueous solution due to rapid quenching of emitted light and adsorption of pulse energy by surrounding water. A method is proposed for the in situ underwater LIES analysis of Cr(VI) in aqueous solution freed from the common problems mentioned above by combining a gas-assisted localized liquid discharge apparatus with electrosorption for the first time. In this approach, the introduction of the gas assisted localized liquid discharge apparatus provides an instantaneous gaseous environment for underwater LIES measurement (that is, the transfer of sampling matrix is not needed from aqueous solution to dry state). The preconcentration of Cr(VI) is achieved by electrosorption with a positive potential applied around adsorbents, which can promote the adsorption of Cr(VI) and inhibit that of the coexisting cations leading to a good anti interference. Amino groups functionalized chitosan-modified graphene oxide (CS-GO) is utilized for Cr(VI) enrichment, which can be protonated to form NH3+ in acidic condition promoting the adsorption toward Cr(VI) by electrostatic attraction. The highest detection sensitivity of 5.15 counts mu g(-1) L toward Cr(VI) is found for the optimized electrosorption potential (E-Es = 1.5 V) and electrosorption time (t(Es) = 600 s) without interference from coexisting metal ions. A corresponding limit of detection (LOD) of 12.3 mu g L-1 (3 sigma method) is achieved, which is amazingly improved by 2 or even 3 orders of magnitude compared to the previous reports of LIES.

LIES; Spatial confinement; Enrichment of graphite; Heavy metal in water;INDUCED BREAKDOWN SPECTROSCOPY; CHROMIUM; CHINA

According to the need of heavy metal pollution detection in waste water. Pure graphite flake is selected as matrix material, the LIBS method of multiple enrichment of samples combined with spatial confinement is adopted to detect the heavy metals contained in the waste water, and spectral stability and limit of detection of Pb, Cu, Cd and Ni are also analyzed. The experiments uses a wavelength of 1 064 nm Nd : YAG Laser, and a optical spectrometer, which the resolution is less than 0. 1 nm to detect the characteristic spectrum of heavy metal elements content in water. The result shows that this method serves to improve sensitivity and spectral stability of heavy metal in waste water while reducing the limit of detection of heavy metals. The intensity of characteristic spectrum are about 2. 5 times better than it under the condition of non-confinement, the spectral stability has also been improved, RSD is reduced from 11.34% to 8.77% compared with non-confinement condition. The calibration curves of four heavy metal elements have been established, the limits of detection of Pb, Cu, Cd and Ni are lower than 1/6 of discharge standard of national industrial waste water, meeting the demand of heavy metal in industrial waste water online monitoring. This method provides a convincing support for discharge control and online monitoring of warning excessive discharge of heavy metal elements in industrial waste water.

Laser-induced breakdown spectroscopy(LIBS); Electrode enrichment; Limit of detection; Heavy metal in water;INDUCED BREAKDOWN SPECTROSCOPY

In order to improve the detection sensitivity of laser-induced breakdown spectroscopy (LIES) and lower the limit of the detection of elements, LIBS combined with Aluminum electrode enrichment method is adopted to analyze heavy metals such as Pb, Cdand Ni in the water. The relationship between the characteristic spectral intensity and the key parameters-voltage of electrode method is discussed, the spectral intensity increases first and then decreases with the increase of voltage. The spectral intensity reaches-the maximum value when the enrichment voltage is 1.2 V while the optimal enrichment voltage value is 1.2 V. The stability of characteristic spectral lines of heavy metals is studied, and the relative standard deviation(RSD) of spectral intensity of Pb, Cd and Ni is 5.98%, 4.25 % and 5.27% respectively, the result shows that the spectral line obtained by this method has high stability. A series of samples in the range of 0 similar to 0.13mg.L-1 are prepared and quantitatively analyzed, the limit of detection of Pb, Cd and Ni is obtained 1.2, 3.1 and 1.7 ppb respectively. The above result shows that LTBS combined with aluminum electrode enrichment method can effectively improve the stability of characteristic spectral lines and lower the limit of detection of Pb,Cd and Ni. This research also provides a method to further improve detection sensitivity of LIES and analysis ability of heavy metal in the water.

Laser-induced breakdown spectroscopy; Orthogonal dual-pulse; Spectral enhancement; Signal-to-background ratio; Plasma temperature; Electron density;OPTICAL-EMISSION; ENHANCEMENT

In order to improve the detection sensitivity and spectral characteristic of laser-induced breakdown spectroscopy (LIES), re-heating orthogonal dual-pulse configuration is adopted to analyze Fe, Pb, Ca and Mg contained in the sample and soil sample contained different concentrations of heavy mental Cr. Variation relationship between spectral intensity, signal-to-background(SBR) of four characteristic spectral lines Fe I : 404. 581 nm, Pb I : 405. 78 nm, Ca I 422. 67 rim and Mg I : 518. 361 nm and time interval of two laser pulses is discussed, the best time interval of two laser pulses is obtained 1. 0 s. In the condition of single pulse and dual-pulse, the enhancement factor of spectral intensity of four characteristic spectral lines Fe I : 404. 581 nm, Pb I : 405. 78 nm, Ca I : 422. 67 nm and Mg I : 518. 361 nm is respectively 2. 23, 2. 31, 2. 42 and 2. 10; The time evolution characteristic of spectral intensity of characteristic spectral lines Fe I : 404. 581 nm and Ca I : 422. 67 rim is considered, and also the variation relationship between spectral acquisition delay time and SBR of-four characteristic spectral lines, dual-pulse can prolong decay time of spectral intensity and improve the SBR of characteristic spectral lines; time evolution characteristic of plasma temperature and electron density is compared in the condition of single pulse and dual-pulse, maximum elevation of plasma temperature is found to be 730 K, and the maximum increase of electron density is 1. 8 X 10(16) cm(-3). The limits of detection of heavy mental Cr are obtained 38 and 20 mu g center dot g(-1) respectively in condition of single and double pulse, limit of detection of Cr is reduced approximately 2 times by the condition of re-heating orthogonal dual pulse. Results above indicate that reheating orthogonal dual-pulse can improve detection sensibility and spectral characteristic of LIBS technique, which provides an effective method for decreasing the limit of detection of elements.