INDUCED BREAKDOWN SPECTROSCOPY; MOLECULAR-EMISSION; LASER; AIR; SPECTROMETRY; CHLORINE

The determination of fluorine in solid samples using Laser Induced Breakdown Spectroscopy (LIBS) is a challenging task due to the low excitation efficiency of this element. Recently, the use of molecular CaF bands was demonstrated to improve the analytical capabilities of LIBS fluorine detection in Ca-containing samples. In this work, a novel approach has been developed to extend this methodology for fluorine quantification in calcium-free samples. In particular, the on-line nebulization of a Ca-containing solution on the surface of a fluorine containing sample has been successfully evaluated to obtain the desired CaF molecular emission. Nebulization parameters have been optimized in order to maximize the molecular emission. A linear relationship between the CaF molecular emission signal and the amount of F in the solid samples has been obtained. The calculated limit of detection for fluorine (about 50 mu g g(-1)) is in the same order of magnitude as that obtained for Ca-containing samples. This novel approach for fluorine quantification opens new ways for the analysis of halogens in solid samples.

LIBS; Gunshot residues; Distance estimation; Forensic analysis; Imaging;INDUCED BREAKDOWN SPECTROSCOPY; FIRING DISTANCE; IMAGE-ANALYSIS; FABRICS; SHOOTER; HANDS; DARK

The study of gunshot residue (GSR) patterns can assist in the reconstruction of shooting incidences. Currently, there is a real need of methods capable of furnishing simultaneous elemental analysis with higher specificity for the GSR pattern visualization. Laser-Induced Breakdown Spectroscopy (LIBS) provides a multi-elemental analysis of the sample, requiring very small amounts of material and no sample preparation. Due to these advantages, this study aims at exploring the potential of LIBS imaging for the visualization of GSR patterns. After the spectral characterization of individual GSR particles, the distribution of Pb, Sb and Ba over clothing targets, shot from different distances, were measured in laser raster mode. In particular, an array of spots evenly spaced at 800 mm, using a stage displacement velocity of 4 mm/s and a laser frequency of 5 Hz was employed (e.g. an area of 130 x 165 mm(2) was measured in less than 3 h). A LIBS set-up based on the simultaneous use of two spectrographs with iCCD cameras and a motorized stage was used. This set-up allows obtaining information from two different wavelength regions (258-289 and 446-463 nm) from the same laser induced plasma, enabling the simultaneous detection of the three characteristic elements (Pb, Sb, and Ba) of GSR particles from conventional ammunitions. The ability to visualize the 2D distribution GSR pattern by LIBS may have an important application in the forensic field, especially for the ballistics area. (C) 2017 Elsevier B.V. All rights reserved.