Discriminating organic carbon from endokarstic moonmilk-type deposits by LIBS. The case of a natural carbonated Martian analogue.

Moonmilk-type deposits exemplify carbonated Martian analogues existing in the subsurface of Earth, an endokarstic speleothem with a possible biochemical origin composed principally by carbonates, mainly huntite and dolomite. In this work, samples of moonmilk located in Nerja Cave (southern Spain) have been studied by LIBS with the aim of identifying carbon of biogenic origin by establishing a relationship between a molecular emission indicator, CN signal, and the organic carbon content. The characterization of this kind of carbonate deposit with a multiple mineralogical composition has been completed using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray diffraction techniques for qualitative and semi-quantitative analysis. The information attained from LIBS regarding energy thresholds and time-resolved kinetics of CN emissions provides useful insight into the identification of different molecular emitters, namely organic and inorganic CN, depending on the laser irradiance and time settings conditions. These promising results are of application in the search and identification of biosignatures in upcoming planetary missions with astrobiological purposes.

Multi-analytical characterization of an oncoid from a high altitude hypersaline lake using techniques employed in the Mars2020 and Rosalind Franklin missions on Mars.

In this work, a geological sample of great astrobiological interest was studied through analytical techniques that are currently operating in situ on Mars and others that will operate in the near future. The sample analyzed consisted of an oncoid, which is a type of microbialite, collected in the Salar Carachi Pampa, Argentina. The main peculiarity of microbialites is that they are organo-sedimentary deposits formed by the in situ fixation and precipitation of calcium carbonate due to the growth and metabolic activities of microorganisms. For this reason, the Carachi Pampa oncoid was selected as a Martian analog for astrobiogeochemistry study. In this sense, the sample was characterized by means of the PIXL-like, SuperCam-like and SHERLOC-like instruments, which represent instruments on board the NASA Perseverance rover, and by means of RLS-like and MOMA-like instruments, which represent instruments on board the future ESA Rosalind Franklin rover. It was possible to verify that the most important conclusions and discoveries have been obtained from the combination of the results. Likewise, it was also shown that Perseverance rover-like remote-sensing instruments allowed a first detailed characterization of the biogeochemistry of the Martian surface. With this first characterization, areas of interest for in-depth analysis with Rosalind Franklin-like instruments could be identified. Therefore, from a first remote-sensing elemental identification (PIXL-like instrument), followed by a remote-sensing molecular characterization (SuperCam and SHERLOC-like instruments) and ending with an in-depth microscopic analysis (RLS and MOMA-like instruments), a wide variety of compounds were found. On the one hand, the expected minerals were carbonates, such as aragonite, calcite and high-magnesium calcite. On the other hand, unexpected compounds consisted of minerals related to the Martian/terrestrial surface (feldspars, pyroxenes, hematite) and organic compounds related to the past biological activity related to the oncoid (kerogen, lipid biomarkers and carotenes). Considering samples resembling microbialites have already been found on Mars and that one of the main objectives of the missions is to identify traces of past life, the study of microbialites is a potential way to find biosignatures protected from the inhospitable Martian environment. In addition, it should be noted that in this work, further conclusions have been obtained through the study of the results as a whole, which could also be carried out on Mars.

Spectrochemical study for the in situ detection of oil spill residues using laser-induced breakdown spectroscopy.

Laser-induced breakdown spectroscopy (LIBS) has been used to identify the differences or similarities between crude oil and fuel residues. Firstly, a man portable LIBS analyzer was used for the on-site environmental control and analysis of the oil spill from The Prestige. An exhaustive analysis of crude oil and oil spill residues (collected during the field campaign in the Galician Coast) was performed in the laboratory. Characteristics elements in petroleum such as C, H, N, O, Mg, Na, Fe and V were detected. In addition, contributions from Ca, Si and Al in the composition of residues have been found. The use of intensity ratios of line and band emissions in the original fuel (crude oil) and in the aged residues allowed a better characterization of the samples than the simple use of peak intensities. The chemical composition between the crude oil and the fuel residues was found completely different. As well, a statistical method was employed in order to discriminate residues. Although significant differences were observed, no conclusions in terms of age and provenance could be reached due to the unknowledgment in the origin of the samples.

Man-portable laser-induced breakdown spectroscopy system for in situ characterization of karstic formations.

This paper reports the development and field testing of a man-portable instrument based on laser-induced breakdown spectrometry (LIBS) for inspection and analysis of speleothems. The 50 mJ of a Q-switched Nd:YAG laser operating at 1064 nm was used to generate a plasma on the sample. Plasma emission was then guided using a fiber-optic cable to a 1/10 m spectrometer equipped with a charge-coupled device (CCD) array detector. Plasma light was automatically processed in order to obtain surface and in-depth information from the speleothems. A field campaign in the interior of Nerja Cave (a large karstic formation in the South of Spain) has been carried out, aimed at evaluating the analytical performance of the instrument when operating in an unfriendly environment. Identification analysis of the speleothems' alteration layers and depth profiles of Sr and Ca is carried out and reported.

Optical restriction of plasma emission light for nanometric sampling depth and depth profiling of multilayered metal samples.

Improvement in depth profiling capabilities of laser-induced breakdown spectrometry (LIBS) for multilayered samples has been attempted. For this purpose, in a typical LIBS experiment, an optical restriction consisting of a pinhole placed between the dichroic mirror and the collecting lenses has been used. This new optical approach allows observing only the light emission coming from the central region of the plume. The microplasma was created on the sample by a pulsed Nd:YAG laser operating at 1064 nm with a homogeneous distribution of energy across the beam. Light emitted by the microplasma was detected with an intensified charge-coupled device (iCCD) multichannel detector. The effect of pinhole diameter and the delay time influence on depth analysis have been assessed. An ablation range of only a few nanometers per pulse has been achieved. Depth profiles of various metals (Cr, Ni, Cu) from multilayered samples have been generated by LIBS and depth resolution at different delay times using various pinhole diameters have been calculated and compared.

In situ analytical assessment and chemical imaging of historical buildings using a man-portable laser system.

In this work, the capability of laser-induced breakdown spectrometry for the in situ analytical assessment and chemical mapping of the façade of the cathedral of Malaga (Spain) has been demonstrated. The task required the use of a portable laser analyzer that allowed real-time spectral acquisitions in the field. A man-portable laser, based on a Q-switched Nd:YAG laser operating at its fundamental wavelength, has been utilized to generate a LIBS plasma of the sample surface. A chemical characterization of the different materials employed in the construction of this building has been performed. The purpose of this study was to use LIBS spectrochemical analysis to qualitatively discriminate between sandstone, limestone, marble, and cement mortar, which are the main components used in this class of historical monument. The field analysis was performed in two zones: the northern façade and the "girola"; the total areas of analysis of the two regions were 250 m(2) and 650 m(2), respectively. Chemical images of Si/Ca and Ca/Mg ratios from both parts of the building were generated. During the measurement campaign, a protocol of analysis was chosen so as to achieve an accurate description of the building materials with respectable spatial resolutions.

Automated line-focused laser ablation for mapping of inclusions in stainless steel.

An automated line imaging arrangement for two-dimensional (2D) and three-dimensional (3D) generation of chemical maps of inclusions in stainless steel by laser-induced plasma spectrometry (LIPS) is presented. The plasma was generated in air at atmospheric pressure by focusing a flat-top Nd:YAG laser beam operating at 532 nm to a microline on the sample surface. The emitted light from the microline plasma was projected through an imaging spectrograph onto a charge-coupled device (CCD) detector to generate a spatially and spectrally resolved data set. Compositional distribution maps of inclusion constituents (Mn, Mg, Ca, Al, and Ti) in stainless steel of different grades have been generated. Comparative studies with the point-to-point LIPS mapping method have been performed, resulting in a 51-fold reduction in the number of pulses and analysis time when the microline imaging approach is employed. The results illustrate the capability of microline imaging LIPS for fast-automated acquisition of tomographic maps with spatial resolution of 50 microm between adjacent craters and 4.8 microm along the microline.

Chemical imaging using microline laser ablation: performance comparison of Gaussian and flat top lasers.

In previous studies, the potential of a microline imaging arrangement for surface characterization of solid samples in air at atmospheric pressure using laser-induced plasma spectrometry (LIPS) has been demonstrated. An improvement of this approach to obtain a uniform ablation along the microline focus that leads to a representative spatial distribution of elements on the sample surface is presented. For this purpose, the influence of beam energy distribution of two types of Nd:YAG pulsed lasers (a Gaussian laser and a flat top laser) on lateral resolution, intensity profiles of elements, chemical distribution maps, and plasma electron temperature has been investigated. As models of homogeneous and compositionally patterned samples, a stainless steel sample and a photovoltaic cell were chosen for this study. The results demonstrated that the Gaussian laser provides the best lateral resolution, but more redeposition at both sides of the microline crater, while the chemical maps obtained with the flat top laser matched with the distribution of the constituents of the sample surface.

Time-resolved laser-induced plasma spectrometry for determination of minor elements in steelmaking process samples.

A pulsed Nd:YAG laser operating on the fourth (266 nm) and second (532 nm) harmonics has been used to generate plasmas on the target surface in air at atmospheric pressure. The influence of wavelength on quantitative analysis of 4 minor elements in stainless steel samples (Si, Ti, Nb and Mo) was investigated. Stainless steel samples with different elemental concentrations were prepared and analyzed by laser-induced plasma spectrometry (LIPS). The effect of laser wavelength on analytical figures of merit (calibration curves, correlation coefficients, linear dynamic ranges, analytical precision, and accuracy values) was found to be negligible when internal standardization (an Fe line) and time-resolved laser-induced plasma are employed. For both wavelengths, the calibration curves presented a good linearity and an acceptable linear dynamic range in the concentration interval investigated. For the four elements studied, limits of detection lower than 150 microg g(-1) were achieved. To evaluate the influence of wavelength on precision and accuracy, a set of fifteen high-alloyed steel samples from different stages of steelmaking process have been analyzed. Finally, the long-term stability of the analytical measurements for Mo with 532 nm wavelength has been discussed. RSD values were lower than 5.3% for the elements studied.

Laser induced breakdown spectrometry of vanadium in titania supported silica catalysts.

The capability of laser induced breakdown spectrometry (LIBS) for vanadium determination in a xV-2TiO(2)-SiO(2) catalyst is presented. The microplasma was generated onto the sample surface using a pulsed Nd:YAG laser operating in the second harmonic (532 nm). Laser produced plasmas were collected and detected using a charge-coupled device (CCD). In order to minimize the complex spectral interferences of emission lines and matrix effects a wide spectral range (210-660 nm) was studied. The focusing of the laser beam on the surface was optimized to improve the signal-to-background ratio, and consequently the limit of detection. The analytical lines selected were used to evaluate the calibration curve. The detection limit for V was estimated to be 38 mug g(-1) in 2TiO(2)-SiO(2). The method precision expressed as relative standard deviation (RSD) was better than 6% in the concentration range 200-1000 mug g(-1).

Sample illumination configurations for spatially resolved Raman spectrometry using a charge-coupled device detector.

In this paper two simple configurations for sample illumination using a charge-coupled device (CCD) detector have been shown. The choice of an appropriate sample illumination can be crucial to obtain spatial and spectral information of complex samples. It is demonstrated that simultaneous Raman spectra of a heterogeneous sample of three compounds can be obtained using a vertical sample illumination. Spatially resolved resonant Raman and surface-enhanced resonant Raman spectra of a complex (Ni-PAPH) have been observed with a low integration time. Dividing the CCD in two region; and with horizontal multiline sample illumination (argon-ion laser at 488 nm and HeNe laser at 632.8 nm) spatially resolved fluorescence spectra of a homogeneous mixture of dyes have been obtained. The total image was acquired in only 1 s.

Surface-enhanced Raman spectrometry for detection in liquid chromatography using a windowless flow cell.

A windowless flow cell has been developed for surface-enhanced Raman (SER) detection in liquid chromatography. Using colloidal silver as an active substrate, SER spectrometry of banned drugs in sport is presented. The experimental factors of primary influence on the analytical performance of the cell have been studied. The results of SER detection with the proposed cell have been compared to UV detection.