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Laser-induced breakdown spectroscopy for light elements detection in steel: State of the art
21 February 2013,
15:50:38
1 March 2013
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
The development of a direct, rapid, and sensitive spectroscopic method for the analytical quantification of light (low atomic number) elements represents an important ongoing challenge. For the first time, we review the evolution of laser-induced breakdown spectroscopy (LIBS) technique for trace analysis of light elements in steels. We present studies carried out in both far/vacuum UV and UV–visible spectral regions, and focus on the elements carbon, sulfur, phosphorous, and nitrogen as their presence and content determine key properties of all steel products. In order to facilitate tracking down the evolution of the technique for a particular element/matrix, the review is organized in such a way that a chronological order has always been obeyed. Moreover, important information regarding characterization of a specific element in a given steel sample is tabulated, so that interested readers can easily locate relevant resources. Furthermore, typical examples of recent developments and advances in terms of LIBS instrumentation and systems regarding light elements in steels are summarized. Finally, the article suggests in brief some approaches for further raising the analytical capability and figures of merit of LIBS regarding trace compositional analysis of light elements. In this respect, we suggest combining LIBS with recently developed diode laser-based techniques such as DLIFS and DLAAS.
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
The development of a direct, rapid, and sensitive spectroscopic method for the analytical quantification of light (low atomic number) elements represents an important ongoing challenge. For the first time, we review the evolution of laser-induced breakdown spectroscopy (LIBS) technique for trace analysis of light elements in steels. We present studies carried out in both far/vacuum UV and UV–visible spectral regions, and focus on the elements carbon, sulfur, phosphorous, and nitrogen as their presence and content determine key properties of all steel products. In order to facilitate tracking down the evolution of the technique for a particular element/matrix, the review is organized in such a way that a chronological order has always been obeyed. Moreover, important information regarding characterization of a specific element in a given steel sample is tabulated, so that interested readers can easily locate relevant resources. Furthermore, typical examples of recent developments and advances in terms of LIBS instrumentation and systems regarding light elements in steels are summarized. Finally, the article suggests in brief some approaches for further raising the analytical capability and figures of merit of LIBS regarding trace compositional analysis of light elements. In this respect, we suggest combining LIBS with recently developed diode laser-based techniques such as DLIFS and DLAAS.
Highlights
► We review development of the LIBS technique for trace analysis of light elements. ► This includes recent advances in laser pulse structure and industrial LIBS systems. ► Detection of light elements by LIBS in the optical region is still difficult. ► LIBS combination with either DLIFS or DLAAS would represent a potential solution.A dried urine spot test to simultaneously monitor Mo and Ti levels using solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry
21 February 2013,
15:50:38
1 March 2013
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
Home-based collection protocols for clinical specimens are actively pursued as a means of improving life quality of patients that require frequent controls, such as patients with metallic prosthesis, for whom monitoring the evolution of Mo and Ti in biological fluids may play a decisive role to detect prosthesis mal-functioning. The collection of biological fluids on clinical filter papers provides a simple way to implement these protocols. This work explores the potential of solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry for the simultaneous and direct determination of Mo and Ti in urine, after its deposition onto clinical filter paper, giving rise to a dried urine spot. The approach used for depositing the sample was found crucial to develop a quantitative method, since the filter paper acts as a chromatographic support and produces a differential distribution of the target analytes. Furthermore, the high spreading of urine onto a filter paper results in a small amount of urine per surface unit, and thus, ultimately, in lack of sensitivity. In order to circumvent these problems, the use of an alternative approach based on the use of pre-cut 17×19mm filter paper pieces onto which larger amounts of sample (500μL) can be retained by single deposition was proposed and evaluated. In this way, an approximately 12-fold increase in sensitivity and a more homogeneous distribution of the target analytes were obtained, permitting the development of a quantification strategy based on the use of matrix-matched urine samples of known analyte concentrations, which were subjected to the same procedure as the samples. Accuracy of this method, which provides LODs of 1.5μgL−1 for Mo and 6.5μgL−1 for Ti, was demonstrated after analysis of urine reference materials. Overall, the performance of the method developed is promising, being likely suitable for determination of other analytes in dried urine spots.
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
Home-based collection protocols for clinical specimens are actively pursued as a means of improving life quality of patients that require frequent controls, such as patients with metallic prosthesis, for whom monitoring the evolution of Mo and Ti in biological fluids may play a decisive role to detect prosthesis mal-functioning. The collection of biological fluids on clinical filter papers provides a simple way to implement these protocols. This work explores the potential of solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry for the simultaneous and direct determination of Mo and Ti in urine, after its deposition onto clinical filter paper, giving rise to a dried urine spot. The approach used for depositing the sample was found crucial to develop a quantitative method, since the filter paper acts as a chromatographic support and produces a differential distribution of the target analytes. Furthermore, the high spreading of urine onto a filter paper results in a small amount of urine per surface unit, and thus, ultimately, in lack of sensitivity. In order to circumvent these problems, the use of an alternative approach based on the use of pre-cut 17×19mm filter paper pieces onto which larger amounts of sample (500μL) can be retained by single deposition was proposed and evaluated. In this way, an approximately 12-fold increase in sensitivity and a more homogeneous distribution of the target analytes were obtained, permitting the development of a quantification strategy based on the use of matrix-matched urine samples of known analyte concentrations, which were subjected to the same procedure as the samples. Accuracy of this method, which provides LODs of 1.5μgL−1 for Mo and 6.5μgL−1 for Ti, was demonstrated after analysis of urine reference materials. Overall, the performance of the method developed is promising, being likely suitable for determination of other analytes in dried urine spots.
Highlights
► Deposition of urine on clinical filters facilitates home-based collection schemes. ►SS HR CS GFAAS enables direct determination of Mo and Ti in urine dried spots. ► These elements may be used as biomarkers to detect prosthesis malfunctioning. ► The way in which the sample is deposited in the filter is a key to proper quantitation. ► The use of matrix-matched urine standards for calibration is recommended.Production of metastable 23S1 helium in a laser produced plasma at low pressures
21 February 2013,
15:50:38
1 March 2013
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
We used cavity ringdown spectroscopy to study how the laser ablation of various materials (graphite, aluminum and iron) influences production of 23 S 1 metastable helium in the regime of low pressure helium gas. Plasma was produced by nanosecond Nd:YAG laser at 1064nm with irradiance from 0.8 to 10.9×109 W/cm2. Helium pressure ranged from 0.03 to 0.2mbar. It was found that at higher irradiances, metastable production for all materials reaches saturation due to plasma shielding and is more pronounced for graphite. The highest yield of metastables was found in the case of aluminum target (0.05%). For metals, production rate is discussed in terms of work function and ionization potential.
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
We used cavity ringdown spectroscopy to study how the laser ablation of various materials (graphite, aluminum and iron) influences production of 23 S 1 metastable helium in the regime of low pressure helium gas. Plasma was produced by nanosecond Nd:YAG laser at 1064nm with irradiance from 0.8 to 10.9×109 W/cm2. Helium pressure ranged from 0.03 to 0.2mbar. It was found that at higher irradiances, metastable production for all materials reaches saturation due to plasma shielding and is more pronounced for graphite. The highest yield of metastables was found in the case of aluminum target (0.05%). For metals, production rate is discussed in terms of work function and ionization potential.
Highlights
► Production and decay of 23 S 1 metastable He upon laser ablation were studied. ► Various targets in the regime of low helium gas pressures were used. ► CRDS was employed for lineshape measurements of the He 388.8nm transition. ► At larger fluences highest yield of metastables was obtained for aluminum target.Spectroscopic characterization of atmospheric pressure argon plasmas sustained with the Torche à Injection Axiale sur Guide d'Ondes
21 February 2013,
15:50:38
1 March 2013
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
An argon microwave (2.45GHz) plasma produced by a microwave plasma torch known as “Torche à Injection Axiale sur Guide d'Ondes” (TIAGO) in air ambience at atmospheric pressure was experimentally characterized. The conditions for appropriate TIAGO torch operation in argon and flame morphology were researched under several experimental conditions of gas flow (0.15–5.00L·min–1) rates and microwave input powers (100–1000W). Gas temperature and electron density values were studied by means of optical emission spectroscopy. Besides, the processes inside the discharge and their interaction with the surrounding atmosphere were described according to the recorded spectra.
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
An argon microwave (2.45GHz) plasma produced by a microwave plasma torch known as “Torche à Injection Axiale sur Guide d'Ondes” (TIAGO) in air ambience at atmospheric pressure was experimentally characterized. The conditions for appropriate TIAGO torch operation in argon and flame morphology were researched under several experimental conditions of gas flow (0.15–5.00L·min–1) rates and microwave input powers (100–1000W). Gas temperature and electron density values were studied by means of optical emission spectroscopy. Besides, the processes inside the discharge and their interaction with the surrounding atmosphere were described according to the recorded spectra.
Highlights
► Ar discharges generated with microwave TIAGO torch were studied by OES. ► Great influence of atmosphere surrounding the flame on discharge parameters ► Electron densities ranging from 1014 cm−3 to 1015 cm−3 depending on argon flow rate ► Gas temperatures ranging from 2500K to 6000K depending on gas flow rate ► Small impact of input power on electron density and gas temperatureThe influence of the sample introduction system on signals of different tin compounds in inductively coupled plasma-based techniques
21 February 2013,
15:50:38
1 March 2013
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
The influence of the sample introduction system on the signals obtained with different tin compounds in inductively coupled plasma (ICP) based techniques, i.e., ICP atomic emission spectrometry (ICP–AES) and ICP mass spectrometry (ICP–MS) has been studied. Signals for test solutions prepared from four different tin compounds (i.e., tin tetrachloride, monobutyltin, dibutyltin and di-tert-butyltin) in different solvents (methanol 0.8% (w/w), i-propanol 0.8% (w/w) and various acid matrices) have been measured by ICP–AES and ICP–MS. The results demonstrate a noticeable influence of the volatility of the tin compounds on their signals measured with both techniques. Thus, in agreement with the compound volatility, the highest signals are obtained for tin tetrachloride followed by di-tert-butyltin/monobutyltin and dibutyltin. The sample introduction system exerts an important effect on the amount of solution loading the plasma and, hence, on the relative signals afforded by the tin compounds in ICP–based techniques. Thus, when working with a pneumatic concentric nebulizer, the use of spray chambers affording high solvent transport efficiency to the plasma (such as cyclonic and single pass) or high spray chamber temperatures is recommended to minimize the influence of the tin chemical compound. Nevertheless, even when using the conventional pneumatic nebulizer coupled to the best spray chamber design (i.e., a single pass spray chamber), signals obtained for di-tert-butyltin/monobutyltin and dibutyltin are still around 10% and 30% lower than the corresponding signal for tin tetrachloride, respectively. When operating with a pneumatic microconcentric nebulizer coupled to a 50°C-thermostated cinnabar spray chamber, all studied organotin compounds provided similar emission signals although about 60% lower than those obtained for tin tetrachloride. The use of an ultrasonic nebulizer coupled to a desolvation device provides the largest differences in the emission signals, among all tested systems.
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
The influence of the sample introduction system on the signals obtained with different tin compounds in inductively coupled plasma (ICP) based techniques, i.e., ICP atomic emission spectrometry (ICP–AES) and ICP mass spectrometry (ICP–MS) has been studied. Signals for test solutions prepared from four different tin compounds (i.e., tin tetrachloride, monobutyltin, dibutyltin and di-tert-butyltin) in different solvents (methanol 0.8% (w/w), i-propanol 0.8% (w/w) and various acid matrices) have been measured by ICP–AES and ICP–MS. The results demonstrate a noticeable influence of the volatility of the tin compounds on their signals measured with both techniques. Thus, in agreement with the compound volatility, the highest signals are obtained for tin tetrachloride followed by di-tert-butyltin/monobutyltin and dibutyltin. The sample introduction system exerts an important effect on the amount of solution loading the plasma and, hence, on the relative signals afforded by the tin compounds in ICP–based techniques. Thus, when working with a pneumatic concentric nebulizer, the use of spray chambers affording high solvent transport efficiency to the plasma (such as cyclonic and single pass) or high spray chamber temperatures is recommended to minimize the influence of the tin chemical compound. Nevertheless, even when using the conventional pneumatic nebulizer coupled to the best spray chamber design (i.e., a single pass spray chamber), signals obtained for di-tert-butyltin/monobutyltin and dibutyltin are still around 10% and 30% lower than the corresponding signal for tin tetrachloride, respectively. When operating with a pneumatic microconcentric nebulizer coupled to a 50°C-thermostated cinnabar spray chamber, all studied organotin compounds provided similar emission signals although about 60% lower than those obtained for tin tetrachloride. The use of an ultrasonic nebulizer coupled to a desolvation device provides the largest differences in the emission signals, among all tested systems.
Highlights
► Tin ICP-based signals depend on the compound chemical form. ► Signal differences are related to the compound volatility. ► Signal differences are reduced using high efficient sample introduction systems.Laser ablation methods for analysis of urinary calculi: Comparison study based on calibration pellets
21 February 2013,
15:50:38
1 March 2013
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
Methods based on laser ablation, such as Laser-Induced Breakdown Spectroscopy (LIBS) and Laser-Ablation Inductively Coupled Plasma Mass/Optical Emission Spectrometry (LA-ICP-MS/OES) are particularly suitable for urinary calculi bulk and micro analysis. Investigation of spatial distribution of matrix and trace elements can help to explain their emergence and growth. However, quantification is still very problematic and these methods are often used only for qualitative elemental mapping. There are no commercially available standards, which would correspond to the urinary calculi matrix. Internal standardization is also difficult, mainly due to different crystalline phases in one kidney stone. The aim of this study is to demonstrate the calibration capabilities and examine the limitations of laser ablation based techniques. Calibration pellets were prepared from powdered human urinary calculi with phosphate, oxalate and urate matrix. For this comparative study, the most frequently used laser-ablation based analytical techniques were chosen, such as LIBS and LA-ICP-MS. Moreover, some alternative techniques such as simultaneous LIBS–LA-ICP-OES and laser ablation LA-LIBS were also utilized.
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
Methods based on laser ablation, such as Laser-Induced Breakdown Spectroscopy (LIBS) and Laser-Ablation Inductively Coupled Plasma Mass/Optical Emission Spectrometry (LA-ICP-MS/OES) are particularly suitable for urinary calculi bulk and micro analysis. Investigation of spatial distribution of matrix and trace elements can help to explain their emergence and growth. However, quantification is still very problematic and these methods are often used only for qualitative elemental mapping. There are no commercially available standards, which would correspond to the urinary calculi matrix. Internal standardization is also difficult, mainly due to different crystalline phases in one kidney stone. The aim of this study is to demonstrate the calibration capabilities and examine the limitations of laser ablation based techniques. Calibration pellets were prepared from powdered human urinary calculi with phosphate, oxalate and urate matrix. For this comparative study, the most frequently used laser-ablation based analytical techniques were chosen, such as LIBS and LA-ICP-MS. Moreover, some alternative techniques such as simultaneous LIBS–LA-ICP-OES and laser ablation LA-LIBS were also utilized.
Highlights
► In this study we compare several laser-ablation based analytical techniques. ► The aim is to prove the calibration capabilities and limitations of these methods. ► Calibration pellets were prepared from human urinary calculi. ► Simultaneous LIBS–LA-ICP-OES, LA-ICP-MS and LA-LIBS were utilized.Backscattered electron images, X-ray maps and Monte Carlo simulations applied to the study of plagioclase composition in volcanic rocks
21 February 2013,
15:50:38
1 March 2013
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
Zoning patterns in plagioclases are related to abrupt changes in the anorthite content along the crystal growing direction. Accurate characterization of these patterns by electron microprobe is useful to identify magma chamber processes such as recharge, mingling and whole-chamber overturn events. In this work, a new procedure to obtain high resolution quantitative maps of anorthite concentration in single plagioclase crystals is developed. The methodology consists of performing a calibration of backscattered electron images using quantitative X-ray maps. The ultimate resolution of characteristic X-rays and backscattered electron signals is studied by Monte Carlo simulation. The method is applied to characterize the chemical composition of a volcanic plagioclase from the Cerro Vilama, Argentina. The results obtained are more precise than the values given by the methods commonly used in the study of plagioclase composition, i.e. the classical profiling by electron microprobe point analysis or the modern backscattered electron image calibration by means of quantitative energy or wavelength dispersive X-ray analysis at a few selected points.
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
Zoning patterns in plagioclases are related to abrupt changes in the anorthite content along the crystal growing direction. Accurate characterization of these patterns by electron microprobe is useful to identify magma chamber processes such as recharge, mingling and whole-chamber overturn events. In this work, a new procedure to obtain high resolution quantitative maps of anorthite concentration in single plagioclase crystals is developed. The methodology consists of performing a calibration of backscattered electron images using quantitative X-ray maps. The ultimate resolution of characteristic X-rays and backscattered electron signals is studied by Monte Carlo simulation. The method is applied to characterize the chemical composition of a volcanic plagioclase from the Cerro Vilama, Argentina. The results obtained are more precise than the values given by the methods commonly used in the study of plagioclase composition, i.e. the classical profiling by electron microprobe point analysis or the modern backscattered electron image calibration by means of quantitative energy or wavelength dispersive X-ray analysis at a few selected points.
Highlights
► High resolution maps of anorthite content in single plagioclase crystals were obtained. ► The procedure was tested on volcanic rocks and is suitable for more evolved plagioclases. ► The ultimate resolution of X-rays and BE signal were studied by Monte Carlo simulations. ► MC simulations allowed to explain the BE contrast enhancement due to interface crossing.Separate K-line contributions to fluorescence enhancement in electron probe microanalysis
21 February 2013,
15:50:38
1 March 2013
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
The behaviour of the fluorescence enhancement correction factor in electron probe microanalysis, as a function of incident electron energy and take-off angle, is assessed for different binary samples in a wide range of compositions. Monte Carlo simulations are employed to validate Reed's correction algorithm [S.J.B. Reed, Characteristic fluorescence corrections in electron-probe microanalysis, Br. J. Appl. Phys. 16 (1965) 913-926], by means of estimating the primary excited radiation volume and the volume corresponding to secondary fluorescence generation. Then, Reed's expression for the fluorescence enhancement has been modified to account for Kα and Kβ line contributions separately. It is clearly shown that in certain cases the assignment of all fluorescent contribution to the Kα lines may be inadequate, particularly when trace element analysis imposes an accurate determination of elemental concentrations.
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
The behaviour of the fluorescence enhancement correction factor in electron probe microanalysis, as a function of incident electron energy and take-off angle, is assessed for different binary samples in a wide range of compositions. Monte Carlo simulations are employed to validate Reed's correction algorithm [S.J.B. Reed, Characteristic fluorescence corrections in electron-probe microanalysis, Br. J. Appl. Phys. 16 (1965) 913-926], by means of estimating the primary excited radiation volume and the volume corresponding to secondary fluorescence generation. Then, Reed's expression for the fluorescence enhancement has been modified to account for Kα and Kβ line contributions separately. It is clearly shown that in certain cases the assignment of all fluorescent contribution to the Kα lines may be inadequate, particularly when trace element analysis imposes an accurate determination of elemental concentrations.
Highlights
► The fluorescence enhancement correction factor in EPMA is studied. ► Reed's correction formulae were modified to account for Kβ and Kα lines separately. ► The differences evidenced encourage the implementation of complete F corrections. ► Trace elemental concentrations may demand complete assessment of fluorescence factor.Application of multivariate curve resolution-alternating least squares for the determination of boron isotope ratios by inductively coupled plasma-optical emission spectrometry
21 February 2013,
15:50:38
1 March 2013
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
Multivariate curve resolution-alternating least squares (MCR-ALS) was applied to atomic emission data obtained from inductively coupled plasma-optical emission spectrometry analysis of boron for the quantification of 10B/11B ratios. The determination of isotopic composition of boron is based on the isotopic shift of 10B and 11B in the emission line of 208.957nm. After recording of the emission spectra in the range of 208.940–208.970 nm, evaluation of isotopic composition of boron containing samples was performed with MCR-ALS algorithm. MCR-ALS was able to resolve the emission spectra of 10B and 11B mixtures. The performance of the proposed methods was tested by determination of 10B/11B ratios in synthetic mixtures and also water samples.
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 81
Multivariate curve resolution-alternating least squares (MCR-ALS) was applied to atomic emission data obtained from inductively coupled plasma-optical emission spectrometry analysis of boron for the quantification of 10B/11B ratios. The determination of isotopic composition of boron is based on the isotopic shift of 10B and 11B in the emission line of 208.957nm. After recording of the emission spectra in the range of 208.940–208.970 nm, evaluation of isotopic composition of boron containing samples was performed with MCR-ALS algorithm. MCR-ALS was able to resolve the emission spectra of 10B and 11B mixtures. The performance of the proposed methods was tested by determination of 10B/11B ratios in synthetic mixtures and also water samples.
Highlights
► A new method for the determination of boron isotope ratios by ICP-OES is proposed. ► It is based on the isotopic shift of 10B and 11B in the emission line of 208.957nm. ► MCR-ALS was used for the resolution of the atomic emission spectra of boron isotopes. ► The proposed method presents good statistical parameters.Pre-Flight Calibration and Initial Data Processing for the ChemCam Laser-Induced Breakdown Spectroscopy Instrument on the Mars Science Laboratory Rover
21 February 2013,
15:50:38
Available online 18 February
2013
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy
The ChemCam instrument package on the Mars Science Laboratory (MSL) rover, Curiosity, is the first planetary science instrument to employ laser-induced breakdown spectroscopy (LIBS) to determine the compositions of geological samples on another planet. Pre-processing of the spectra involves subtracting the ambient light background, removing noise, removing the electron continuum, calibrating for the wavelength, correcting for the variable distance to the target, and applying a wavelength-dependent correction for the instrument response. Further processing of the data uses multivariate and univariate comparisons with a LIBS spectral library developed prior to launch as well as comparisons with several on-board standards post-landing. The level-2 data products include semi-quantitative abundances derived from partial least squares (PLS) regression. A LIBS spectral library was developed using 69 rock standards in the form of pressed powder disks, glasses, and ceramics to minimize heterogeneity on the scale of the observation (350-550μm dia.). The standards covered typical compositional ranges of igneous materials and also included sulfates, carbonates, and phyllosilicates. The provenance and elemental and mineralogical compositions of these standards are described. Spectral characteristics of this data set are presented, including the size distribution and integrated irradiances of the plasmas, and a proxy for plasma temperature as a function of distance from the instrument. Two laboratory-based clones of ChemCam reside in Los Alamos and Toulouse for the purpose of adding new spectra to the database as the need arises. Sensitivity to differences in wavelength correlation to spectral channels and spectral resolution has been investigated, indicating that spectral registration needs to be within half a pixel and resolution needs to match within 1.5 to 2.6 pixels. Absolute errors are tabulated for derived compositions of each major element in each standard using PLS regression. Sources of errors are investigated and discussed, and methods for improving the analytical accuracy of compositions derived from ChemCam spectra are discussed.
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy
The ChemCam instrument package on the Mars Science Laboratory (MSL) rover, Curiosity, is the first planetary science instrument to employ laser-induced breakdown spectroscopy (LIBS) to determine the compositions of geological samples on another planet. Pre-processing of the spectra involves subtracting the ambient light background, removing noise, removing the electron continuum, calibrating for the wavelength, correcting for the variable distance to the target, and applying a wavelength-dependent correction for the instrument response. Further processing of the data uses multivariate and univariate comparisons with a LIBS spectral library developed prior to launch as well as comparisons with several on-board standards post-landing. The level-2 data products include semi-quantitative abundances derived from partial least squares (PLS) regression. A LIBS spectral library was developed using 69 rock standards in the form of pressed powder disks, glasses, and ceramics to minimize heterogeneity on the scale of the observation (350-550μm dia.). The standards covered typical compositional ranges of igneous materials and also included sulfates, carbonates, and phyllosilicates. The provenance and elemental and mineralogical compositions of these standards are described. Spectral characteristics of this data set are presented, including the size distribution and integrated irradiances of the plasmas, and a proxy for plasma temperature as a function of distance from the instrument. Two laboratory-based clones of ChemCam reside in Los Alamos and Toulouse for the purpose of adding new spectra to the database as the need arises. Sensitivity to differences in wavelength correlation to spectral channels and spectral resolution has been investigated, indicating that spectral registration needs to be within half a pixel and resolution needs to match within 1.5 to 2.6 pixels. Absolute errors are tabulated for derived compositions of each major element in each standard using PLS regression. Sources of errors are investigated and discussed, and methods for improving the analytical accuracy of compositions derived from ChemCam spectra are discussed.
Highlights
► We describe a LIBS spectral training set of 69 geological standards. ► ChemCam Mars LIBS data processing is described. Detection limits are given. ► Laser coupling, plasma temperature, accuracy, and precision are detailed.Non-linear signal response functions and their effects on the statistical and noise cancellation properties of isotope ratio measurements by multi-collector plasma mass spectrometry
21 February 2013,
15:50:38
Available online 16 February
2013
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy
A nebulizer-centric response function model of the analytical inductively coupled argon plasma ion source was used to investigate the statistical frequency distributions and noise reduction factors of simultaneously measured flicker noise limited isotope ion signals and their ratios. The response function model was extended by assuming i) a single gaussian distributed random noise source (nebulizer gas pressure fluctuations) and ii) the isotope ion signal response is a parabolic function of the nebulizer gas pressure. Model calculations of ion signal and signal ratio histograms were obtained by applying the statistical method of translation to the non-linear response function model of the plasma. Histograms of Ni, Cu, Pr, Tl and Pb isotope ion signals measured using a multi-collector plasma mass spectrometer were, without exception, negative skew. Histograms of the corresponding isotope ratios of Ni, Cu, Tl and Pb were either positive or negative skew. There was complete agreement between the measured and model calculated histogram skew properties. The nebulizer-centric response function model was also used to investigate the effect of non-linear response functions on the effectiveness of noise cancellation by signal division. An alternative noise correction procedure suitable for parabolic signal response functions was derived and applied to measurements of isotope ratios of Cu, Ni, Pb and Tl. The largest noise reduction factors were always obtained when the non-linearity of the response functions was taken into account by the isotope ratio calculation. Possible applications of the nebulizer-centric response function model to other types of analytical instrumentation, large amplitude signal noise sources (e.g., lasers, pumped nebulizers) and analytical error in isotope ratio measurements by multi-collector plasma mass spectrometry are discussed.
Publication year: 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy
A nebulizer-centric response function model of the analytical inductively coupled argon plasma ion source was used to investigate the statistical frequency distributions and noise reduction factors of simultaneously measured flicker noise limited isotope ion signals and their ratios. The response function model was extended by assuming i) a single gaussian distributed random noise source (nebulizer gas pressure fluctuations) and ii) the isotope ion signal response is a parabolic function of the nebulizer gas pressure. Model calculations of ion signal and signal ratio histograms were obtained by applying the statistical method of translation to the non-linear response function model of the plasma. Histograms of Ni, Cu, Pr, Tl and Pb isotope ion signals measured using a multi-collector plasma mass spectrometer were, without exception, negative skew. Histograms of the corresponding isotope ratios of Ni, Cu, Tl and Pb were either positive or negative skew. There was complete agreement between the measured and model calculated histogram skew properties. The nebulizer-centric response function model was also used to investigate the effect of non-linear response functions on the effectiveness of noise cancellation by signal division. An alternative noise correction procedure suitable for parabolic signal response functions was derived and applied to measurements of isotope ratios of Cu, Ni, Pb and Tl. The largest noise reduction factors were always obtained when the non-linearity of the response functions was taken into account by the isotope ratio calculation. Possible applications of the nebulizer-centric response function model to other types of analytical instrumentation, large amplitude signal noise sources (e.g., lasers, pumped nebulizers) and analytical error in isotope ratio measurements by multi-collector plasma mass spectrometry are discussed.
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