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Thermodynamic equilibrium states in laser-induced plasmas: From the general case to laser-induced breakdown spectroscopy plasmas
28 October 2013,
09:52:48
Publication date: 1 December
2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 90
Author(s): G. Cristoforetti , E. Tognoni , L.A. Gizzi
Applications, present and potential, of laser-induced plasmas are today widespread in a large range of fields and continue to extend each day because of the advancement of laser science and technology. These circumstances call for a better knowledge and characterization of physical and chemical processes occurring in a plasma. The spectrum of the radiation emitted by the plasmas is a mine of information about the plasma state and therefore spectroscopy remains one of the key techniques for its investigation. The interpretation of emission spectra, however, requires a deep knowledge of the elementary processes determining the atomic state population and the fractional ion densities, and of their balance. The transient character of laser-induced plasmas and the presence of spatial gradients introduce time-dependent and non-local effects in the energy level population, and thus increase the complexity of the plasma modeling. The thermodynamic approach, describing the atomic and ionic state population by statistical distributions, is the easiest and the most widely used way to model the plasma state but does not account for non-local and non-steady-state effects. It is therefore in many cases unfit for this purpose. As a consequence, kinetic modeling of the plasma is often needed, which must be in many cases integrated by hydrodynamic modeling of plasma expansion and appropriate equations describing the transport of radiation and charged particles into the plasma. In this complex framework, this paper aims at giving a concise description of theoretical issues, redirecting to the key literature for more details, and to delineate possible scenarios occurring in the wide range of laser-induced plasmas. Examples of different classes of laser-induced plasmas are reported, including some experimental results for completeness. Special attention is devoted to the case of ‘cold’ or thermal plasmas, in particular those produced in laser-induced breakdown spectroscopy. The occurrence of local thermodynamic equilibrium is, in that case, discussed as well as the relevance of phenomena leading the system out of equilibrium, such as radiative, transient and diffusive processes. The most important directions for future work, in particular regarding non-stationary and diffusive effects, are also suggested.
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 90
Author(s): G. Cristoforetti , E. Tognoni , L.A. Gizzi
Applications, present and potential, of laser-induced plasmas are today widespread in a large range of fields and continue to extend each day because of the advancement of laser science and technology. These circumstances call for a better knowledge and characterization of physical and chemical processes occurring in a plasma. The spectrum of the radiation emitted by the plasmas is a mine of information about the plasma state and therefore spectroscopy remains one of the key techniques for its investigation. The interpretation of emission spectra, however, requires a deep knowledge of the elementary processes determining the atomic state population and the fractional ion densities, and of their balance. The transient character of laser-induced plasmas and the presence of spatial gradients introduce time-dependent and non-local effects in the energy level population, and thus increase the complexity of the plasma modeling. The thermodynamic approach, describing the atomic and ionic state population by statistical distributions, is the easiest and the most widely used way to model the plasma state but does not account for non-local and non-steady-state effects. It is therefore in many cases unfit for this purpose. As a consequence, kinetic modeling of the plasma is often needed, which must be in many cases integrated by hydrodynamic modeling of plasma expansion and appropriate equations describing the transport of radiation and charged particles into the plasma. In this complex framework, this paper aims at giving a concise description of theoretical issues, redirecting to the key literature for more details, and to delineate possible scenarios occurring in the wide range of laser-induced plasmas. Examples of different classes of laser-induced plasmas are reported, including some experimental results for completeness. Special attention is devoted to the case of ‘cold’ or thermal plasmas, in particular those produced in laser-induced breakdown spectroscopy. The occurrence of local thermodynamic equilibrium is, in that case, discussed as well as the relevance of phenomena leading the system out of equilibrium, such as radiative, transient and diffusive processes. The most important directions for future work, in particular regarding non-stationary and diffusive effects, are also suggested.
Production of aerosols by optical catapulting: Imaging, performance parameters and laser-induced plasma sampling rate
28 October 2013,
09:52:48
Publication date: 1 November
2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): M. Abdelhamid , F.J. Fortes , A. Fernández-Bravo , M.A. Harith , J.J. Laserna
Optical catapulting (OC) is a sampling and manipulation method that has been extensively studied in applications ranging from single cells in heterogeneous tissue samples to analysis of explosive residues in human fingerprints. Specifically, analysis of the catapulted material by means of laser-induced breakdown spectroscopy (LIBS) offers a promising approach for the inspection of solid particulate matter. In this work, we focus our attention in the experimental parameters to be optimized for a proper aerosol generation while increasing the particle density in the focal region sampled by LIBS. For this purpose we use shadowgraphy visualization as a diagnostic tool. Shadowgraphic images were acquired for studying the evolution and dynamics of solid aerosols produced by OC. Aluminum silicate particles (0.2–8μm) were ejected from the substrate using a Q-switched Nd:YAG laser at 1064nm, while time-resolved images recorded the propagation of the generated aerosol. For LIBS analysis and shadowgraphy visualization, a Q-switched Nd:YAG laser at 1064nm and 532nm was employed, respectively. Several parameters such as the time delay between pulses and the effect of laser fluence on the aerosol production have been also investigated. After optimization, the particle density in the sampling focal volume increases while improving the aerosol sampling rate till ca. 90%.
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): M. Abdelhamid , F.J. Fortes , A. Fernández-Bravo , M.A. Harith , J.J. Laserna
Optical catapulting (OC) is a sampling and manipulation method that has been extensively studied in applications ranging from single cells in heterogeneous tissue samples to analysis of explosive residues in human fingerprints. Specifically, analysis of the catapulted material by means of laser-induced breakdown spectroscopy (LIBS) offers a promising approach for the inspection of solid particulate matter. In this work, we focus our attention in the experimental parameters to be optimized for a proper aerosol generation while increasing the particle density in the focal region sampled by LIBS. For this purpose we use shadowgraphy visualization as a diagnostic tool. Shadowgraphic images were acquired for studying the evolution and dynamics of solid aerosols produced by OC. Aluminum silicate particles (0.2–8μm) were ejected from the substrate using a Q-switched Nd:YAG laser at 1064nm, while time-resolved images recorded the propagation of the generated aerosol. For LIBS analysis and shadowgraphy visualization, a Q-switched Nd:YAG laser at 1064nm and 532nm was employed, respectively. Several parameters such as the time delay between pulses and the effect of laser fluence on the aerosol production have been also investigated. After optimization, the particle density in the sampling focal volume increases while improving the aerosol sampling rate till ca. 90%.
Use of portable X-ray fluorescence instrument for bulk alloy analysis on low corroded indoor bronzes
28 October 2013,
09:52:48
Publication date: 1 November
2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): D. Šatović , V. Desnica , S. Fazinić
One of the most often used non-destructive methods for elemental analysis when performing field measurements on bronze sculptures is X-ray fluorescence (XRF) analysis based on portable instrumentation. However, when performing routine in-situ XRF analysis on corroded objects obtained results are sometimes considerably influenced by the corrosion surface products. In this work the suitability of portable XRF for bulk analysis of low corroded bronzes, which were initially precisely characterized using sophisticated and reliable laboratory methods, was investigated and some improvements in measuring technique and data processing were given. Artificially corroded bronze samples were analyzed by a portable XRF instrument using the same methodology and procedures as when performing in-situ analysis on real objects. The samples were first investigated using sophisticated complementary laboratory techniques: Scanning Electron Microscopy, Proton-Induced X-ray Emission Spectroscopy and Rutherford Backscattering Spectrometry, in order to gain precise information on the formation of the corrosion product layers and in-depth elemental profile of corrosion layers for different aging parameters. It has been shown that for corrosion layers of up to ca. 25μm a portable XRF can yield very accurate quantification results.
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): D. Šatović , V. Desnica , S. Fazinić
One of the most often used non-destructive methods for elemental analysis when performing field measurements on bronze sculptures is X-ray fluorescence (XRF) analysis based on portable instrumentation. However, when performing routine in-situ XRF analysis on corroded objects obtained results are sometimes considerably influenced by the corrosion surface products. In this work the suitability of portable XRF for bulk analysis of low corroded bronzes, which were initially precisely characterized using sophisticated and reliable laboratory methods, was investigated and some improvements in measuring technique and data processing were given. Artificially corroded bronze samples were analyzed by a portable XRF instrument using the same methodology and procedures as when performing in-situ analysis on real objects. The samples were first investigated using sophisticated complementary laboratory techniques: Scanning Electron Microscopy, Proton-Induced X-ray Emission Spectroscopy and Rutherford Backscattering Spectrometry, in order to gain precise information on the formation of the corrosion product layers and in-depth elemental profile of corrosion layers for different aging parameters. It has been shown that for corrosion layers of up to ca. 25μm a portable XRF can yield very accurate quantification results.
Common analyte internal standardization as a tool for correction for mass discrimination in multi-collector inductively coupled plasma-mass spectrometry
28 October 2013,
09:52:48
Publication date: 1 November
2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Veerle Devulder , Lara Lobo , Karen Van Hoecke , Patrick Degryse , Frank Vanhaecke
It is well known that to achieve accurate isotope ratio data using multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS), mass discrimination needs to be adequately corrected for. In this work, the capabilities and limitations of common analyte internal standardization (CAIS) as a method for correction for mass discrimination were assessed for two target elements, one in the low mass region (boron) and another in the medium mass region (antimony). CAIS has already been used in the context of element determination and, more recently, also in isotope ratio measurements with quadrupole-based ICP-MS, but it has, to the best of the authors' knowledge, never been applied to isotope ratio determination via MC-ICP-MS so far. Results obtained relying on CAIS were compared with those obtained via more established correction models, i.e. external correction in a standard-sample bracketing approach (SSB) and internal correction based on both the Russell's law (original and empirical) and the revised Russell's law. To the best of the authors' knowledge, such comparison has not been done before, especially not for low mass elements. Also the robustness of these approaches with respect to concomitant matrix elements was assessed using synthetic solutions, containing various concentrations of the matrix elements Be, Cs, Be+Cs or Fe. Whereas for B, the isotope ratio result did not seem to be significantly affected by the matrix, thus suggesting that complete separation of B from a matrix might not be necessary, at least in the cases studied, the mass discrimination observed for Sb was influenced by the presence of Cs. The experiments carried out demonstrate that the CAIS technique can be successfully applied for mass bias correction in MC-ICP-MS, providing data of the same quality as the revised Russell's law, while being more transparent and accessible. While for B, all mass bias correction approaches tested provided similar data quality (external correction with SSB gives slightly better precision), for Sb, CAIS and the revised Russell's law provide better precision and accuracy.
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Veerle Devulder , Lara Lobo , Karen Van Hoecke , Patrick Degryse , Frank Vanhaecke
It is well known that to achieve accurate isotope ratio data using multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS), mass discrimination needs to be adequately corrected for. In this work, the capabilities and limitations of common analyte internal standardization (CAIS) as a method for correction for mass discrimination were assessed for two target elements, one in the low mass region (boron) and another in the medium mass region (antimony). CAIS has already been used in the context of element determination and, more recently, also in isotope ratio measurements with quadrupole-based ICP-MS, but it has, to the best of the authors' knowledge, never been applied to isotope ratio determination via MC-ICP-MS so far. Results obtained relying on CAIS were compared with those obtained via more established correction models, i.e. external correction in a standard-sample bracketing approach (SSB) and internal correction based on both the Russell's law (original and empirical) and the revised Russell's law. To the best of the authors' knowledge, such comparison has not been done before, especially not for low mass elements. Also the robustness of these approaches with respect to concomitant matrix elements was assessed using synthetic solutions, containing various concentrations of the matrix elements Be, Cs, Be+Cs or Fe. Whereas for B, the isotope ratio result did not seem to be significantly affected by the matrix, thus suggesting that complete separation of B from a matrix might not be necessary, at least in the cases studied, the mass discrimination observed for Sb was influenced by the presence of Cs. The experiments carried out demonstrate that the CAIS technique can be successfully applied for mass bias correction in MC-ICP-MS, providing data of the same quality as the revised Russell's law, while being more transparent and accessible. While for B, all mass bias correction approaches tested provided similar data quality (external correction with SSB gives slightly better precision), for Sb, CAIS and the revised Russell's law provide better precision and accuracy.
Considerations of particle vaporization and analyte diffusion in single-particle inductively coupled plasma-mass spectrometry
28 October 2013,
09:52:48
Publication date: 1 November
2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Koon-Sing Ho , Kwok-On Lui , Kin-Ho Lee , Wing-Tat Chan
The intensity of individual gold nanoparticles with nominal diameters of 80, 100, 150, and 200nm was measured using single-particle inductively coupled plasma-mass spectrometry (ICP-MS). Since the particles are not perfectly monodisperse, a distribution of ICP-MS intensity was obtained for each nominal diameter. The distribution of particle mass was determined from the transmission electron microscopy (TEM) image of the particles. The distribution of ICP-MS intensity and the distribution of particle mass for each nominal diameter were correlated to give a calibration curve. The calibration curves are linear, but the slope decreases as the nominal diameter increases. The reduced slope is probably due to a smaller degree of vaporization of the large particles. In addition to the degree of particle vaporization, the rate of analyte diffusion in the ICP is an important factor that determines the measured ICP-MS intensity. Simulated ICP-MS intensity versus particle size was calculated using a simple computer program that accounts for the vaporization rate of the gold nanoparticles and the diffusion rate and degree of ionization of the gold atoms. The curvature of the simulated calibration curves changes with sampling depth because the effects of particle vaporization and analyte diffusion on the ICP-MS intensity are dependent on the residence time of the particle in the ICP. Calibration curves of four hypothetical particles representing the four combinations of high and low boiling points (2000 and 4000K) and high and low analyte diffusion rates (atomic masses of 10 and 200Da) were calculated to further illustrate the relative effects of particle vaporization and analyte diffusion. The simulated calibration curves show that the sensitivity of single-particle ICP-MS is smaller than that of the ICP-MS measurement of continuous flow of standard solutions by a factor of 2 or more. Calibration using continuous flow of standard solution is semi-quantitative at best. An empirical equation is formulated for the estimation of the position of complete vaporization of a particle in the ICP. The equation takes into account the particle properties (diameter, density, boiling point, and molecular weight of the constituents of the particle) and the ICP operating parameters (ICP forward power and central channel gas flow rate). The proportional constant and exponents of the variables in the equation were solved using literature values of ICP operating conditions for single-particle inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-atomic emission spectrometry (ICP-AES) measurements of 6 kinds of particles in 12 studies. The calculated position is a useful guide for the selection of sampling depth or observation height for ICP-MS and ICP-AES measurements of single particles as well as discrete particles in a flow, such as laser-ablated materials and airborne particulates.
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Koon-Sing Ho , Kwok-On Lui , Kin-Ho Lee , Wing-Tat Chan
The intensity of individual gold nanoparticles with nominal diameters of 80, 100, 150, and 200nm was measured using single-particle inductively coupled plasma-mass spectrometry (ICP-MS). Since the particles are not perfectly monodisperse, a distribution of ICP-MS intensity was obtained for each nominal diameter. The distribution of particle mass was determined from the transmission electron microscopy (TEM) image of the particles. The distribution of ICP-MS intensity and the distribution of particle mass for each nominal diameter were correlated to give a calibration curve. The calibration curves are linear, but the slope decreases as the nominal diameter increases. The reduced slope is probably due to a smaller degree of vaporization of the large particles. In addition to the degree of particle vaporization, the rate of analyte diffusion in the ICP is an important factor that determines the measured ICP-MS intensity. Simulated ICP-MS intensity versus particle size was calculated using a simple computer program that accounts for the vaporization rate of the gold nanoparticles and the diffusion rate and degree of ionization of the gold atoms. The curvature of the simulated calibration curves changes with sampling depth because the effects of particle vaporization and analyte diffusion on the ICP-MS intensity are dependent on the residence time of the particle in the ICP. Calibration curves of four hypothetical particles representing the four combinations of high and low boiling points (2000 and 4000K) and high and low analyte diffusion rates (atomic masses of 10 and 200Da) were calculated to further illustrate the relative effects of particle vaporization and analyte diffusion. The simulated calibration curves show that the sensitivity of single-particle ICP-MS is smaller than that of the ICP-MS measurement of continuous flow of standard solutions by a factor of 2 or more. Calibration using continuous flow of standard solution is semi-quantitative at best. An empirical equation is formulated for the estimation of the position of complete vaporization of a particle in the ICP. The equation takes into account the particle properties (diameter, density, boiling point, and molecular weight of the constituents of the particle) and the ICP operating parameters (ICP forward power and central channel gas flow rate). The proportional constant and exponents of the variables in the equation were solved using literature values of ICP operating conditions for single-particle inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-atomic emission spectrometry (ICP-AES) measurements of 6 kinds of particles in 12 studies. The calculated position is a useful guide for the selection of sampling depth or observation height for ICP-MS and ICP-AES measurements of single particles as well as discrete particles in a flow, such as laser-ablated materials and airborne particulates.
Multiple emission line analysis for improved isotopic determination of uranium — a computer simulation study
28 October 2013,
09:52:48
Publication date: 1 November
2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): George C.-Y. Chan , Xianglei Mao , Inhee Choi , Arnab Sarkar , Oanh P. Lam , David K. Shuh , Richard E. Russo
Forty-three atomic emission lines for 235U and 238U were compiled for computer simulation of isotopic analysis using laser induced breakdown spectroscopy (LIBS). The spectral line profile was assumed to be Lorentzian in shape and the magnitude of three common types of noises (detector-read, photon-shot and flicker) were experimentally determined and incorporated into the simulation. Precision and root mean square error of prediction (RMSEP) for isotopic analysis of a single U line were simulated, and it was found that analytical performance (precision) primarily depended on the signal-to-background ratio (SBR) and net intensity of the emission line, rather than on the magnitude of isotopic splitting (IS), when partial least squares (PLS) was used for calibration. This is because PLS multivariate calibration can be performed correctly even when the spectra are only partially resolved, which in turn relaxes the requirement on having IS larger than the spectral resolution. The analytical performance was found to improve with multiple-line analysis. Depending on the criteria (e.g., SBR, net intensity, magnitude of IS, or best single-line performance) used in sorting the spectral lines into the multiline pool, improvement factors ranging from 2× to 9× were obtained. The absolute uncertainty of isotopic analysis is practically constant and independent of isotopic abundance, which makes experimental estimation of the detection limit in isotopic analysis straightforward because one can experimentally measure this uncertainty with one arbitrary and conveniently chosen isotopic standard and then estimate the detection limit through simple extrapolation.
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): George C.-Y. Chan , Xianglei Mao , Inhee Choi , Arnab Sarkar , Oanh P. Lam , David K. Shuh , Richard E. Russo
Forty-three atomic emission lines for 235U and 238U were compiled for computer simulation of isotopic analysis using laser induced breakdown spectroscopy (LIBS). The spectral line profile was assumed to be Lorentzian in shape and the magnitude of three common types of noises (detector-read, photon-shot and flicker) were experimentally determined and incorporated into the simulation. Precision and root mean square error of prediction (RMSEP) for isotopic analysis of a single U line were simulated, and it was found that analytical performance (precision) primarily depended on the signal-to-background ratio (SBR) and net intensity of the emission line, rather than on the magnitude of isotopic splitting (IS), when partial least squares (PLS) was used for calibration. This is because PLS multivariate calibration can be performed correctly even when the spectra are only partially resolved, which in turn relaxes the requirement on having IS larger than the spectral resolution. The analytical performance was found to improve with multiple-line analysis. Depending on the criteria (e.g., SBR, net intensity, magnitude of IS, or best single-line performance) used in sorting the spectral lines into the multiline pool, improvement factors ranging from 2× to 9× were obtained. The absolute uncertainty of isotopic analysis is practically constant and independent of isotopic abundance, which makes experimental estimation of the detection limit in isotopic analysis straightforward because one can experimentally measure this uncertainty with one arbitrary and conveniently chosen isotopic standard and then estimate the detection limit through simple extrapolation.
Optical emission spectroscopy for quantification of ultraviolet radiations and biocide active species in microwave argon plasma jet at atmospheric pressure
28 October 2013,
09:52:48
Publication date: 1 November
2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): G. Wattieaux , M. Yousfi , N. Merbahi
This work deals with absorption and mainly emission spectrometry of a microwave induced surfatron plasma jet launched in ambient air and using an Argon flow carrier gas. The Ar flow rate varies between 1 and 3L/min and the microwave power between 40 and 60W. The analysis of the various spectra has led to the determination of the ozone and atomic oxygen concentrations, ultraviolet (UV) irradiance separating UVA, UVB and UVC, gas temperature, plasma electron density and excitation temperature. Most of these diagnostics are spatially resolved along the plasma jet axis. It is shown more particularly that rotational temperature obtained from OH(A-X) spectra ranges between 800K to 1000K while the apparent temperature of the plasma jet remains lower than about 325K which is compatible with biocide treatment without significant thermal effect. The electron density reaches 1.2×1014 cm−3, the excitation temperature is about 4000K, the UVC radiation represents only 5% of the UV radiations emitted by the device, the ozone concentration is found to reach 88±27ppm in the downstream part of the plasma jet at a distance of 30mm away from the quartz tube outlet of the surfatron and the atomic oxygen concentration lies between 10 and 80ppm up to a distance of 20mm away from the quartz tube outlet. Ozone is identified as the main germicidal active species produced by the device since its concentration is in accordance with bacteria inactivation durations usually reported using such plasma devices. Human health hazard assessment is carried out all along this study since simple solutions are reminded to respect safety standards for exposures to ozone and microwave leakage. In this study, an air extraction unit is used and a Faraday cage is set around the quartz tube of the surfatron and the plasma jet. These solutions should be adopted by users of microwave induced plasma in open air conditions because according to the literature, this is not often the case.
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): G. Wattieaux , M. Yousfi , N. Merbahi
This work deals with absorption and mainly emission spectrometry of a microwave induced surfatron plasma jet launched in ambient air and using an Argon flow carrier gas. The Ar flow rate varies between 1 and 3L/min and the microwave power between 40 and 60W. The analysis of the various spectra has led to the determination of the ozone and atomic oxygen concentrations, ultraviolet (UV) irradiance separating UVA, UVB and UVC, gas temperature, plasma electron density and excitation temperature. Most of these diagnostics are spatially resolved along the plasma jet axis. It is shown more particularly that rotational temperature obtained from OH(A-X) spectra ranges between 800K to 1000K while the apparent temperature of the plasma jet remains lower than about 325K which is compatible with biocide treatment without significant thermal effect. The electron density reaches 1.2×1014 cm−3, the excitation temperature is about 4000K, the UVC radiation represents only 5% of the UV radiations emitted by the device, the ozone concentration is found to reach 88±27ppm in the downstream part of the plasma jet at a distance of 30mm away from the quartz tube outlet of the surfatron and the atomic oxygen concentration lies between 10 and 80ppm up to a distance of 20mm away from the quartz tube outlet. Ozone is identified as the main germicidal active species produced by the device since its concentration is in accordance with bacteria inactivation durations usually reported using such plasma devices. Human health hazard assessment is carried out all along this study since simple solutions are reminded to respect safety standards for exposures to ozone and microwave leakage. In this study, an air extraction unit is used and a Faraday cage is set around the quartz tube of the surfatron and the plasma jet. These solutions should be adopted by users of microwave induced plasma in open air conditions because according to the literature, this is not often the case.
Vibrational emission analysis of the CN molecules in laser-induced breakdown spectroscopy of organic compounds
28 October 2013,
09:52:48
Publication date: 1 November
2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Ángel Fernández-Bravo , Tomás Delgado , Patricia Lucena , J. Javier Laserna
Laser-induced breakdown spectroscopy (LIBS) of organic materials is based on the analysis of atomic and ionic emission lines and on a few molecular bands, the most important being the CN violet system and the C2 Swan system. This paper is focused in molecular emission of LIBS plasmas based on the CN (B2Σ–X2Σ) band, one of the strongest emissions appearing in all carbon materials when analyzed in air atmosphere. An analysis of this band with sufficient spectral resolution provides a great deal of information on the molecule, which has revealed that valuable information can be obtained from the plume chemistry and dynamics affecting the excitation mechanisms of the molecules. The vibrational emission of this molecular band has been investigated to establish the dependence of this emission on the molecular structure of the materials. The paper shows that excitation/emission phenomena of molecular species observed in the plume depend strongly on the time interval selected and on the irradiance deposited on the sample surface. Precise time resolved LIBS measurements are needed for the observation of distinctive CN emission. For the organic compounds studied, larger differences in the behavior of the vibrational emission occur at early stages after plasma ignition. Since molecular emission is generally more complex than that involving atomic emission, local plasma conditions as well as plume chemistry may induce changes in vibrational emission of molecules. As a consequence, alterations in the distribution of the emissions occur in terms of relative intensities, being sensitive to the molecular structure of every single material.
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Ángel Fernández-Bravo , Tomás Delgado , Patricia Lucena , J. Javier Laserna
Laser-induced breakdown spectroscopy (LIBS) of organic materials is based on the analysis of atomic and ionic emission lines and on a few molecular bands, the most important being the CN violet system and the C2 Swan system. This paper is focused in molecular emission of LIBS plasmas based on the CN (B2Σ–X2Σ) band, one of the strongest emissions appearing in all carbon materials when analyzed in air atmosphere. An analysis of this band with sufficient spectral resolution provides a great deal of information on the molecule, which has revealed that valuable information can be obtained from the plume chemistry and dynamics affecting the excitation mechanisms of the molecules. The vibrational emission of this molecular band has been investigated to establish the dependence of this emission on the molecular structure of the materials. The paper shows that excitation/emission phenomena of molecular species observed in the plume depend strongly on the time interval selected and on the irradiance deposited on the sample surface. Precise time resolved LIBS measurements are needed for the observation of distinctive CN emission. For the organic compounds studied, larger differences in the behavior of the vibrational emission occur at early stages after plasma ignition. Since molecular emission is generally more complex than that involving atomic emission, local plasma conditions as well as plume chemistry may induce changes in vibrational emission of molecules. As a consequence, alterations in the distribution of the emissions occur in terms of relative intensities, being sensitive to the molecular structure of every single material.
Application of laser ablation inductively coupled plasma multicollector mass spectometry in determination of lead isotope ratios in common glass for forensic purposes
28 October 2013,
09:52:48
Publication date: 1 November
2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Knut-Endre Sjåstad , Tom Andersen , Siri Lene Simonsen
Samples of glass used as trace evidence in criminal cases are commonly small, with particle sizes below a millimeter. To perform chemical analysis suitable for forensic purposes, methods capable of analyzing such small samples are required. In this paper, analyses of lead isotope ratios by means of laser ablation inductively coupled multicollector mass spectrometry (LA-MC-ICP-MS) are presented. Sampling by use of laser ablation allows fragments down to 0.1mg to be analyzed with sufficient precision to discriminate between glasses of different origin. In fact, the use of lead isotopes determined by LA-MC-ICP-MS approaches the discrimination attainable by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) analysis of dissolved samples of 5mg or more. Further, we have obtained a probability distribution by two dimensional kernel density estimates for the collected data set as an alternative presentation method to the well-established bivariate plot. The underlying information available from kernel density estimates is of importance for forensic scientists involved in probabilistic interpretation of physical evidence.
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Knut-Endre Sjåstad , Tom Andersen , Siri Lene Simonsen
Samples of glass used as trace evidence in criminal cases are commonly small, with particle sizes below a millimeter. To perform chemical analysis suitable for forensic purposes, methods capable of analyzing such small samples are required. In this paper, analyses of lead isotope ratios by means of laser ablation inductively coupled multicollector mass spectrometry (LA-MC-ICP-MS) are presented. Sampling by use of laser ablation allows fragments down to 0.1mg to be analyzed with sufficient precision to discriminate between glasses of different origin. In fact, the use of lead isotopes determined by LA-MC-ICP-MS approaches the discrimination attainable by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) analysis of dissolved samples of 5mg or more. Further, we have obtained a probability distribution by two dimensional kernel density estimates for the collected data set as an alternative presentation method to the well-established bivariate plot. The underlying information available from kernel density estimates is of importance for forensic scientists involved in probabilistic interpretation of physical evidence.
Atomic emission spectroscopy method for mixing studies in high power thermal plasmas
28 October 2013,
09:52:48
Publication date: 1 November
2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Jochen Altenberend , Guy Chichignoud , Yves Delannoy
Atomic emission spectrometry was used to measure the distribution of concentration ratios and temperature in thermal plasmas produced by high power torches for process engineering. The spectroscopic method is based on absolute line intensity measurement and Abel inversion. Assuming local thermal equilibrium, the temperature is deduced from the absolute emission of an argon line and the concentration ratio is deduced from the emission ratio of two lines. Using the two dimensions of the camera for spatial and spectral resolution, fast measurements with high resolution can be done. The method has been tested on a 60kW inductively coupled plasma torch at atmospheric pressure. The results show that the concentration ratios n(O)/n(Ar) and n(H)/n(Ar) can be measured with an accuracy of 25% and that errors due to deviations from LTE are small. Demixing occurs in the induction zone. The application of the method showed that hydrogen diffuses much more than oxygen. The main disadvantage of this method is that, using emission, it does not permit to measure the concentration in the “cold” zones in the center and at the edge of the plasma.
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Jochen Altenberend , Guy Chichignoud , Yves Delannoy
Atomic emission spectrometry was used to measure the distribution of concentration ratios and temperature in thermal plasmas produced by high power torches for process engineering. The spectroscopic method is based on absolute line intensity measurement and Abel inversion. Assuming local thermal equilibrium, the temperature is deduced from the absolute emission of an argon line and the concentration ratio is deduced from the emission ratio of two lines. Using the two dimensions of the camera for spatial and spectral resolution, fast measurements with high resolution can be done. The method has been tested on a 60kW inductively coupled plasma torch at atmospheric pressure. The results show that the concentration ratios n(O)/n(Ar) and n(H)/n(Ar) can be measured with an accuracy of 25% and that errors due to deviations from LTE are small. Demixing occurs in the induction zone. The application of the method showed that hydrogen diffuses much more than oxygen. The main disadvantage of this method is that, using emission, it does not permit to measure the concentration in the “cold” zones in the center and at the edge of the plasma.
In situ atom trapping of Bi on W-coated slotted quartz tube flame atomic absorption spectrometry and interference studies
28 October 2013,
09:52:48
Publication date: 1 November
2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Ersin Kılınç , Sezgin Bakırdere , Fırat Aydın , O. Yavuz Ataman
Analytical performances of metal coated slotted quartz tube flame atomic absorption spectrometry (SQT-FAAS) and slotted quartz tube in situ atom trapping flame atomic absorption spectrometry (SQT-AT-FAAS) systems were evaluated for determination of Bi. Non-volatile elements such as Mo, Zr, W and Ta were tried as coating materials. It was observed that W-coated SQT gave the best sensitivity for the determination of Bi for SQT-FAAS and SQT-AT-FAAS. The parameters for W-coated SQT-FAAS and W-coated SQT-AT-FAAS were optimized. Sensitivity of FAAS for Bi was improved as 4.0 fold by W-coated SQT-FAAS while 613 fold enhancement in sensitivity was achieved by W-coated SQT-AT-FAAS using 5.0min trapping with respect to conventional FAAS. MIBK was selected as organic solvent for the re-atomization of Bi from the trapping surface. Limit of detection values for W-coated SQT-FAAS and W-coated SQT-AT-FAAS was obtained as 0.14μgmL−1 and 0.51ngmL−1, respectively. Linear calibration plot was obtained in the range of 2.5–25.0ngmL−1 for W-coated SQT-AT-FAAS. Accuracy of the W-coated SQT-AT-FAAS system was checked by analyzing a standard reference material, NIST 1643e.
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Ersin Kılınç , Sezgin Bakırdere , Fırat Aydın , O. Yavuz Ataman
Analytical performances of metal coated slotted quartz tube flame atomic absorption spectrometry (SQT-FAAS) and slotted quartz tube in situ atom trapping flame atomic absorption spectrometry (SQT-AT-FAAS) systems were evaluated for determination of Bi. Non-volatile elements such as Mo, Zr, W and Ta were tried as coating materials. It was observed that W-coated SQT gave the best sensitivity for the determination of Bi for SQT-FAAS and SQT-AT-FAAS. The parameters for W-coated SQT-FAAS and W-coated SQT-AT-FAAS were optimized. Sensitivity of FAAS for Bi was improved as 4.0 fold by W-coated SQT-FAAS while 613 fold enhancement in sensitivity was achieved by W-coated SQT-AT-FAAS using 5.0min trapping with respect to conventional FAAS. MIBK was selected as organic solvent for the re-atomization of Bi from the trapping surface. Limit of detection values for W-coated SQT-FAAS and W-coated SQT-AT-FAAS was obtained as 0.14μgmL−1 and 0.51ngmL−1, respectively. Linear calibration plot was obtained in the range of 2.5–25.0ngmL−1 for W-coated SQT-AT-FAAS. Accuracy of the W-coated SQT-AT-FAAS system was checked by analyzing a standard reference material, NIST 1643e.
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