Spatial confinement of laser-induced plasma to enhance LIBS sensitivity for trace elements determination in soils

To improve analytical figures-of-merit of the single-pulse LIBS for determination of trace elements in soil samples, a new configuration for spatial confinement based on a special designed device described recently in our work (A.M. Popov, F. Colao and R. Fantoni, J. Anal. At. Spectrom., 2009, 24, 602–604) was studied. The confinement tool realized is a small chamber (about 4 mm in diameter) equipped with polished brass walls and high efficiency collecting optics. A specific analytical procedure was developed to clean the chamber from impurities of microparticles deposited on surface of its walls after each experiment. Investigating the influence of focusing conditions on the stability of LIBS emission signal we have found that the relative standard deviation (RSD) of LIBS signal decreased as the distance between the focus position and the sample surface increased. So, the optimal position of the focus was found below the sample surface as a compromise between the need of collecting intense emission signals and of avoiding breakdown from the ejected microparticles. A significant intensity enhancement was observed inside the chamber, its use as an analytical tool was deeply investigated. The intensity enhancement, obtained on several major (Fe, Mg, Si) and trace elements (As, Ba, Cr, Hg, Mn, Ni, P, Pb, Ti, V) in the examined samples was significantly larger than the decrease of signal-to-noise ratio associated with the slightly worst statistics in the reproducibility of single-shot spectra inside the chamber. The 3σ-limits of detection (LOD) of As, Hg, Pb, Mn, V and Ba in soil by using the confined plasma were 30, 25, 90, 140, 1 and 50 ppm, respectively, resulting 2–5 times lower than LODs obtained for a free-expanding plasma under the same experimental conditions.

[1]  A. K. Rai,et al.  Screening of brick-kiln area soil for determination of heavy metal Pb using LIBS , 2009, Environmental monitoring and assessment.

[2]  C. Fotakis,et al.  On-Line Monitoring of Laser Cleaning of Limestone by Laser-Induced Breakdown Spectroscopy and Laser-Induced Fluorescence , 1997 .

[3]  Ralph Greif,et al.  Laser–plasma interactions in fused silica cavities , 2003 .

[4]  Z. H. Yamani,et al.  Measurement Of Nutrients In Green House Soil With Laser Induced Breakdown Spectroscopy , 2007, Environmental monitoring and assessment.

[5]  M. Gondal,et al.  Monitoring and assessment of toxic metals in Gulf War oil spill contaminated soil using laser-induced breakdown spectroscopy , 2007, Environmental monitoring and assessment.

[6]  Wolfgang L. Wiese,et al.  Experimental Stark Widths and Shifts for Spectral Lines of Neutral and Ionized Atoms (A Critical Review of Selected Data for the Period 1989 Through 2000) , 2002 .

[7]  R. Noll,et al.  New approach to online monitoring of the Al depth profile of the hot-dip galvanised sheet steel using LIBS , 2006, Analytical and bioanalytical chemistry.

[8]  Roberta Fantoni,et al.  Determination of heavy metals in soils by Laser Induced Breakdown Spectroscopy , 2002 .

[9]  V. Kiris,et al.  Application of emission spectrometer with laser sampler to microanalysis of pigments from Hubert Robert’s canvas painting , 2006 .

[10]  B. Bousquet,et al.  Laser-induced breakdown spectroscopy of composite samples: comparison of advanced chemometrics methods. , 2006, Analytical chemistry.

[11]  S. Amoruso,et al.  Characterization of laser-ablation plasmas , 1999 .

[12]  Yongfeng Lu,et al.  Optical emission in magnetically confined laser-induced breakdown spectroscopy , 2006 .

[13]  David A. Cremers,et al.  Detection of Metals in the Environment Using a Portable Laser-Induced Breakdown Spectroscopy Instrument , 1996 .

[14]  David A. Banks,et al.  Paleo-fluid composition determined from individual fluid inclusions by Raman and LIBS: Application to mid-proterozoic evaporitic Na–Ca brines (Alligator Rivers Uranium Field, northern territories Australia) , 2007 .

[15]  D. Cremers,et al.  Matrix Effects in the Detection of Pb and Ba in Soils Using Laser-Induced Breakdown Spectroscopy , 1996 .

[16]  Reinhard Noll,et al.  Analysis of heavy metals in soils using laser-induced breakdown spectrometry combined with laser-induced fluorescence , 2001 .

[17]  Israel Schechter,et al.  Detector for trace elemental analysis of solid environmental samples by laser plasma spectroscopy , 1994 .

[18]  Robert Fedosejevs,et al.  Detection of lead in water using laser-induced breakdown spectroscopy and laser-induced fluorescence. , 2008, Analytical chemistry.

[19]  Akshaya Kumar,et al.  Effect of steady magnetic field on laser-induced breakdown spectroscopy. , 2003, Applied optics.

[20]  D. Bhadra.  EXPANSION OF A RESISTIVE PLASMOID IN A MAGNETIC FIELD. , 1968 .

[21]  N. B. Zorov,et al.  Selection of an analytical line for determining lithium in aluminum alloys by laser induced breakdown spectrometry , 2007 .

[22]  Stephen H. Lieberman,et al.  A real-time fiber-optic LIBS probe for the in situ delineation of metals in soils† , 1998 .

[23]  David A. Cremers,et al.  Laser-Induced Breakdown Spectroscopy Analysis of Solids Using a Long-Pulse (150 ns) Q-Switched Nd:YAG Laser , 2005, Applied spectroscopy.

[24]  D. Cremers,et al.  Use of the vacuum ultraviolet spectral region for laser-induced breakdown spectroscopy-based Martian geology and exploration , 2005 .

[25]  R. Reuter,et al.  Resonance fluorescence spectroscopy in laser-induced cavitation bubbles , 2006, Analytical and bioanalytical chemistry.

[26]  R. K. Thareja,et al.  Instabilities in laser-produced carbon plasma expanding in a nonuniform magnetic field , 2001 .

[27]  S. N. Isakov,et al.  Analysis of lead and sulfur in environmental samples by double pulse laser induced breakdown spectroscopy , 2009 .

[28]  J. Goldberg,et al.  Production and initial characterization of a laser-induced plasma in a pulsed magnetic field for atomic spectrometry , 1987 .

[29]  Demetrios Anglos,et al.  Laser-induced breakdown spectroscopy (LIBS) in archaeological science—applications and prospects , 2007, Analytical and bioanalytical chemistry.

[30]  D. E. Poulain,et al.  Quantitative Analysis of the Detection Limits for Heavy-Metal-Contaminated Soils by Laser-Induced Breakdown Spectroscopy. , 1997 .

[31]  V. Babushok,et al.  Double pulse laser ablation and plasma: Laser induced breakdown spectroscopy signal enhancement , 2006 .

[32]  Roberta Fantoni,et al.  Enhancement of LIBS signal by spatially confining the laser-induced plasma , 2009 .

[33]  Ronald G. Pinnick,et al.  Aerosol-induced laser breakdown thresholds: wavelength dependence. , 1988, Applied optics.

[34]  Stefano Legnaioli,et al.  Effect of Laser-Induced Crater Depth in Laser-Induced Breakdown Spectroscopy Emission Features , 2005, Applied spectroscopy.

[35]  Yongfeng Lu,et al.  Spectroscopic study of laser-induced Al plasmas with cylindrical confinement , 2007 .

[36]  Roger C. Wiens,et al.  Evaluation of a compact spectrograph for in-situ and stand-off Laser-Induced Breakdown Spectroscopy analyses of geological samples on Mars missions , 2005 .

[37]  David A. Cremers,et al.  Remote Elemental Analysis by Laser-Induced Breakdown Spectroscopy Using a Fiber-Optic Cable , 1995 .

[38]  S. Angel,et al.  Emission enhancement mechanisms in dual-pulse LIBS. , 2006, Analytical chemistry.