laser-induced breakdown spectroscopy; phosphate rocks; organomineral fertilizers; principal components analysis; partial least squares regression;ELEMENTAL ANALYSIS; PLANT MATERIALS; SOIL; CHEMOMETRICS

A number of phosphate rocks and organomineral P fertilizers was analyzed comparatively by laser-induced breakdown spectroscopy (LIBS) in both single- and double-pulse modes associated with two chemometric methods, i.e., principal components analysis (PCA) and partial least squares regression (PLSR). PCA was demonstrated to be a valuable method for the identification of spectral differences between similar samples with only minor compositional differences. The raw and normalized LIBS spectra were able to provide effective identification and discrimination at a 95% confidence level and in good agreement with the reference concentrations. Results obtained confirm the promising potential of LIBS for the rapid classification of P fertilizers in situ.

Coffee global quality; BGS; Classes discrimination; NIRS; LIBS;NEAR-INFRARED SPECTROSCOPY; MARKER COMPOUNDS; CUP QUALITY; BEANS; DEFECTS

Coffee is an important commodity and a very popular beverage around the world. Its economic value as well as beverage quality are strongly dependent of the quality of beans. The presence of defective beans in coffee blends has caused a negative impact on the beverage Global Quality (GQ) assessed by cupping tests. The main defective beans observed in the productive chain has been those Blacks, Greens and Sours (BGS). Chemical composition of BGS has a damaging impact on beverage GQ That is why analytical tools are needed for monitoring and controlling the GQ in coffee agro-industry. Near Infrared Spectroscopy (NIRS) has been successfully applied for assessment of coffee quality. Another potential technique for direct, clean and fast measurement of coffee GQ is Laser Induced Breakdown Spectroscopy (LIBS). Elements and diatomic molecules commonly present in organic compounds (structure) can be assessed by using LIBS. In this article is reported an evaluation of LIBS for the main interferents of GQ (BGS defects). Results confirm the great potential of LIBS for discriminating good beans from those with BGS defects by using emission lines of C, CN, C-2 and N. Most importantly, some emission lines presented strong linear correlation (r > 0.9) with NIRS absorption bands assigned to proteins, lipids, sugar and carboxylic adds, suggesting LIBS potential to estimate these compounds in unroasted and ground coffee samples. (C) 2017 Elsevier B.V. All rights reserved.

Nutritional evaluation; laser-induced breakdown spectroscopy; LIBS; Huanglongbing; HLB; phytosanitary control; diagnosis; data analysis; citrus diseases;GREENING DISEASE; FLUORESCENCE; LIBS; LEAVES; TOOLS

Huanglongbing (HLB) is the most recent and destructive bacterial disease of citrus and has no cure yet. A promising alternative to conventional methods is to use laser-induced breakdown spectroscopy (LIBS), a multi-elemental analytical technique, to identify the nutritional changes provoked by the disease to the citrus leaves and associate the mineral composition profile with its health status. The leaves were collected from adult citrus trees and identified by visual inspection as healthy, HLB-symptomatic, and HLB-asymptomatic. Laser-induced breakdown spectroscopy measurements were done in fresh leaves without sample preparation. Nutritional variations were evaluated using statistical tools, such as Student's t-test and analysis of variance applied to LIBS spectra, and the largest were found for Ca, Mg, and K. Considering the nutritional profile changes, a classifier induced by classification via regression combined with partial least squares regression was built resulting in an accuracy of 73% for distinguishing the three categories of leaves.

Soil; Plant; Fertilizer; DP LIBS analysis; Orthogonal geometry; Ablative energy;SIGNAL ENHANCEMENT; PLANT MATERIALS; PLASMA; LIBS; FERTILIZERS; ABLATION; SOILS; QUANTIFICATION; CONTAMINANTS; DEPENDENCE

A soil, a plant and a fertilizer sample were investigated by double-pulse (DP) laser-induced breakdown spectroscopy (LIBS) in orthogonal beam geometry using a reheating configuration. The DP-LIBS signal enhancement was evaluated with respect to the corresponding single-pulse (SP) LIBS as a function of the interpulse delay at various ablation energies. The maximum signal enhancement measured was 155-fold when low ablation energy (4 mJ) and an interpulse delay of 10 mu s were used. At high laser energies (>= 16 mJ) and interpulse delay of 0.6 mu s, the maximum signal enhancement was up to 3-fold. The effect of excitation energies and interpulse delays on emission line intensities was discussed in the various conditions used. The emission line enhancement measured for ionic lines was always higher than that of atomic lines. Plasma excitation temperature and electron density measured as a function of interpulse delays at various ablation energies were shown to be related to the emission line intensities. (C) 2017 Elsevier B.V. All rights reserved.

SOILS; AGE; LIBS

Laser-induced breakdown spectroscopy (LIBS) is showing to be a promising, quick, accurate, and practical technique to detect and measure metal contaminants and nutrients in urban wastes and landfill leachates. Although conventional LIBS presents some limitations, such as low sensitivity, when used in the single pulse configuration if compared to other spectroscopic techniques, the use of the double-pulse (DP) configuration represents an adequate alternative. In this work DP LIBS has been applied to the qualitative and quantitative analysis of mercury (Hg) in landfill leachates. The correlation analysis performed between each intensified charge-coupled device pixel and the Hg concentration allowed us to choose the most appropriate Hg emission line to be used for its measure. The normalization process applied to LIBS spectra to correct physical matrix effects and small fluctuations increased from 0.82 to 0.98 the linear correlation of the calibration curve between LIBS and the reference data. The limit of detection for Hg estimated using DP LIBS was 76 mg Kg(-1). The cross validation (leave-one-out) analysis yielded an absolute average error of about 21%. These values showed that the calibration models were close to the optimization limit and satisfactory for Hg quantification in landfill leachate. (C) 2017 Optical Society of America

SIGNAL ENHANCEMENT; LIBS; DEPENDENCE; SOIL; MICROANALYSIS; EMISSION; ABLATION; LIQUIDS

Laser-induced breakdown spectroscopy (LIBS) is a technique increasingly used to perform fast semi-quantitative multi-elemental analyses of various materials without any complex sample preparation, being also suitable for in situ analyses. Few studies have been performed to understand the influence of laserwavelength on LIBS analytical performance on environmental samples. The main goal of this study was to perform a comparative elemental analysis of a number of soils, citrus leaves, and synthetic solid matrices using two different wavelengths, i.e., 532 and 1064 nm of Nd: YAG lasers, and a spectrometer coupled to a non-intensified charge-coupled device camera as the detection system. The emission lines with higher upper energy level, i.e., C I-193.03 (7.685 eV) and Si I-212.41 nm (6.616 eV), were more intense when using the 532 nm than the 1064 nm laser light, whereas the opposite occurred for elements with lower upper energy level, i.e., Ti I-336.12 nm (3.716 eV) and Fe I-368.75 nm (4.220 eV). The observed increase in LIBS signal between the two wavelengths is about 30-50%. The relationship between the line emission intensities and the used excitation wavelengths were associated to the upper level energy of the element.