Pressed Powder Pellets Research Articles

Distinction and quantification of inorganic sulfur species including thiosulfate by X‐ray fluorescence (WD‐XRF)

Sulfur occurs in a variety of inorganic and organic compounds with oxidation states from −II up to +VI. Differentiation of these species in solid geochemical samples can be challenging because of oxidation processes during sample preparation by acidic digestion. Applying pressed powder pellets and an analysis by wavelength‐dispersive X‐ray fluorescence minimises reactions with oxidants and water.Main subjects of this work were five inorganic sulfur species, sulfide −II, elemental sulfur 0, thiosulfate +II, sulfite +IV, and sulfate +VI, and the determination of their fluorescence energies in the sulfur X‐ray spectra. S Kα1,2 and S Kβ1 can be observed for all species, S Kβ′ satellites only for species with coordinated oxygen. The results are in good agreement with previously published data. Yet none of the 38 investigated papers from the past 90 years reported S Kα1,2 of thiosulfate, which was determined as E = 2,309.12 eV in this work apparently for the first time.Binary mixtures of sulfur species are strongly differing in their ability of being quantitatively differentiated, as a reliable quantification requires a sufficient difference of the respective fluorescence energies. Regression equations for each mixture can be used to calculate the ratio of mass fractions of the investigated species from the evaluated fluorescence energy.If boundary conditions are considered, the presented approaches can be applied for analyses of geochemical samples or quality control of technical products. The main advantage of the described methods is the option of implementation to everyday X‐ray fluorescence lab routine without substantial additional effort.

Investigation of a high-pressure pressed powder pellet technique for the analysis of coal by wavelength dispersive X-ray fluorescence spectroscopy

Using the proposed high-pressure pressed powder pellet technique, a coal sample was pressed into an ideal pellet without binders, which provides a solution to the poor self-binding quality of coal for the determination by X-ray fluorescence spectroscopy (XRF). The pellet produced by this method was more compact and smoother, which was particularly meaningful for spectrometer, where the sample is placed over the tube window. Additionally, the high-pressure sample preparation technique effectively eliminated the effect of falling powder and contamination in the Measuring chamber of the spectrometer.Wavelength Dispersive X-ray Fluorescence Spectroscopy (WDXRF) was applied successfully to the determination of carbon, nitrogen and ash content in coal samples. This could provide an alternative method for the rapid analysis of carbon, nitrogen and ash content in the coal rather than the combustion method or the high-frequency infrared absorption with a slow ashing method. Furthermore, WDXRF could provide simultaneous determination of other major, minor and trace elements by X-ray fluorescence spectroscopy. The XRF results indicated that the sensitivity, precision, and limit of detection for most components were improved when the coal sample was pressed at 1600kN compared with preparation at 400kN.

Quantitative analysis of major and trace elements in NH4HF2-modified silicate rock powders by laser ablation - inductively coupled plasma mass spectrometry

In this paper, we described a NH4HF2 digestion method as sample preparation for the rapid determination of major and trace elements in silicate rocks using laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS). Sample powders digested by NH4HF2 at 230 °C for 3 h form ultrafine powders with a typical grain size d80 < 8.5 μm, and various silicate rocks have a consistent grain morphology and size, allowing us to produce pressed powder pellets that have excellent cohesion and homogeneity suitable for laser ablation micro-analysis without the addition of binder. The influences of the digestion parameters were investigated and optimized, including the evaporation stage of removing residual NH4HF2, sample homogenization, selection of the digestion vessel and calibration strategy of quantitative analysis. The optimized NH4HF2 digestion method was applied to dissolve six silicate rock reference materials (BCR-2, BHVO-2, AGV-2, RGM-2, GSP-2, GSR-1) covering a wide range of rock types. Ten major elements and thirty-five trace elements were simultaneously analyzed by LA-ICP-MS. The analytical results of the six reference materials generally agreed with the recommended values, with discrepancies of less than 10% for most elements. The analytical precision is within 5% for most major elements and within 10% for most trace elements. Compared with previous methods of LA-ICP-MS bulk analysis, our method enables the complete dissolution of refractory minerals, such as zircon, in intermediate-acidic intrusive rocks and limits contamination as well as the loss of volatile elements. Moreover, there are many advantages for the new technique, including reducing matrix effects between reference materials and samples, spiking the internal standard simply and feasibly and sample batch processing. The applicability filed of the new technique in this study was focused on the whole-rock analysis of igneous rock samples, which are from basic rocks to acid rocks (45% < SiO2 < 73%). However, we thought that the NH4HF2 digestion method can be used as a new alternative in LA-ICP-MS for a wider range of geological samples, and will significantly accelerate the application of LA-ICP-MS for the whole-rock analysis.

Comparison of Fused Glass Beads and Pressed Powder Pellets for the Quantitative Measurement of Al, Fe, Si and Ti in Bauxite by Laser‐Induced Breakdown Spectroscopy

Due to matrix interference and sample particle size effects, some of the most important and difficult issues in laser‐induced breakdown spectroscopy (LIBS) analysis are the calibration and quantitative measurement of a complex matrix. This study proposes the use of borate fusion as an alternative sample preparation procedure for the quantitative measurement of Al, Fe, Si and Ti in bauxite by LIBS. Analytical calibration curves were made using bauxite certified reference materials (CRM), and the precision and accuracy of the methods were evaluated by analysing an additional bauxite CRM, using two different approaches: pressed powder pellets and fused glass beads. The borate fusion method was the most suitable sample preparation technique, since particle size effects and matrix interference could be minimised, obtaining better linearity on the analytical calibration curves (r2), and more accurate and more precise results for bauxite analysis.

Use of X-ray Fluorescence Analysis for the Determination of Rare Earth Elements

AbstractX-ray fluorescence spectrometry (XRF) is a powerful tool for the analysis of solid material. That is the reason why the technique was applied for the determination of rare earth elements (REEs) since about 1970. At present, energy-dispersive XRF and wavelength-dispersive XRF are used for the analysis of pressed powder pellets or fused Li-borate beads containing REEs. The production of reliable results can only be achieved by careful optimization of the parameter, in particular the selection of spectral lines. The quantification is based on a calibration realized by using reference samples.

X‐ray fluorescence determination of sulfur chemical state in sulfide ores

This paper describes the X‐ray fluorescence technique for estimation of the ratio between sulfide and total sulfur in sulfide ores using the influence of sulfur chemical state on positions and intensities of lines (SKα1,2, SKβ1,3) and satellites (SKβ′, SKα3,4) of the sulfur X‐ray emission spectra measured by the wavelength‐dispersive X‐ray fluorescence spectrometer. The samples to be analyzed were prepared as pressed powder pellets on boric acid substrate. The SKα1,2 line chemical shift is the most appropriate parameter for sulfur chemical state estimation because spectral lines in this field are intensive and are almost not affected by spectral overlap of lead spectrum lines. The ratios of line intensities SKβ′/SKβ1,3, SKα3,4/SKα1,2 and SKβ1,3/SKα1,2 were also used as analytical parameters. Forty‐one samples of sulfide ores collected in the Russian Far East and Southern Ural deposits have been analyzed. The results of estimation of sulfur chemical state by gravimetric and proposed X‐ray fluorescence techniques agree fairly well. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Evaluation of Major to Ultra Trace Element Bulk Rock Chemical Analysis of Nanoparticulate Pressed Powder Pellets by LA‐ICP‐MS

An efficient, clean procedure for the measurement of element mass fractions in bulk rock nanoparticulate pressed powder pellets (PPPs) by 193 nm laser ablation ICP‐MS is presented. Samples were pulverised by wet milling and pelletised with microcrystalline cellulose as a binder, allowing non‐cohesive materials such as quartz or ceramics to be processed. The LA‐ICP‐MS PPP analytical procedure was optimised and evaluated using six different geological reference materials (JP‐1, UB‐N, BCR‐2, GSP‐2, OKUM and MUH‐1), with rigorous procedural blank quantification employing synthetic quartz. Measurement trueness of the procedure was equivalent to that achieved by solution ICP‐MS and LA‐ICP‐MS analysis of glass. The measurement repeatability was as low as 0.5–2% (1s, n = 6) and, accordingly, PPP homogeneity could be demonstrated. Calibration based on the reference glasses NIST SRM 610, NIST SRM 612, BCR‐2G and GSD‐1G revealed matrix effects for glass and PPP measurement with NIST SRM 61×; using basalt glasses eliminated this problem. Most significantly, trace elements not commonly measured (flux elements Li, B; chalcophile elements As, Sb, Tl, In, Bi) could be quantified. The PPP‐LA‐ICP‐MS method overcomes common problems and limitations in analytical geochemistry and thus represents an efficient and accurate alternative for bulk rock analysis.

Empirical Approach for Estimating Reference Material Heterogeneity and Sample Minimum Test Portion Mass for "Nuggety" Precious Metals (Au, Pd, Ir, Pt, Ru).

Quantification of precious metal content is important for studies of ore deposits, basalt petrogenesis, and precious metal geology, mineralization, mining, and processing. However, accurate determination of metal concentrations can be compromised by microheterogeneity commonly referred to as the "nugget effect", i.e., spatially significant variations in the distribution of precious metal minerals at the scale of instrumental analytical beam footprints. There are few studies focused on the spatial distribution of such minerals and its detrimental effects on quantification of the existing suite of relevant reference materials (RM). In order to assess the nugget effect in RM, pressed powder pellets of MASS-1, MASS-3, WMS-1a, WMS-1, and KPT-1 (dominantly sulfides) as well as CHR-Pt+ and CHR-Bkg (chromite-bearing) were mapped with micro-XRF. The number of verified nuggets observed was used to recalculate an effective concentration of precious metals for the analytical aliquot, allowing for an empirical estimate of a minimum mass test portion. MASS-1, MASS-3, and WMS-1a did not contain any nuggets; therefore, a convenient small test portion could be used here (<0.1 g), while CHR-Pt+ would require 0.125 g and WMS-1 would need 23 g to be representative. For CHR-Bkg and KPT-1, the minimum test portion mass would have to be ∼80 and ∼342 g, respectively. Minimum test portions masses may have to be greater still in order to provide detectable analytical signals. Procedures for counteracting the detrimental manifestations of microheterogeneity are presented. It is imperative that both RM and pristine samples are treated in exactly the same way in the laboratory, lest powders having an unknown nugget status (in effect all field samples for analysis) can not be documented to be representing a safe minimum mass basis.

Underestimation of chromium and zirconium in soils by hydrofluoric acid digestion and inductively coupled plasma-mass spectrometry

ABSTRACTThe concentrations of chromium (Cr) and zirconium (Zr) in 503 soil samples collected from 78 site in Japan were determined by using two utterly different methods. The first was the relatively widely used inductively coupled plasma-mass spectrometry (ICP-MS) combined with digestion with hydrofluoric acid (HF) and perchloric acid (HClO4). The second was a non-destructive polarizing energy dispersive X-ray fluorescence spectrometric method (EDXRF) using pressed powder pellets. The Cr concentrations obtained by EDXRF were higher than those obtained by ICP-MS in ~75% of the samples. The EDXRF/ICP-MS ratios ranged from 0.48 to 9.65, and the geometric mean was 1.23. A typical example having big a difference in Cr content between the two methods was found in seven samples taken from a podzolic soil developed on sand dunes in northern Hokkaido. This sampling site is around 20 km from the northern edge of a serpentinite area that extends from north to south, forming the backbone mountain range of Hokkaido. The Cr concentrations obtained by ICP-MS for the seven samples were 27.9–52.2 mg kg−1, similar to the average for all the samples, whereas those obtained by EDXRF were 101–460 mg kg−1, falling within the range between the third quartile and the maximum for all the samples. It would be difficult to predict these results from the analytical data of other elements because the samples were high in silica (SiO2) and low in magnesia (MgO), and did not show any characteristics typical of soils derived from serpentinite. X-ray adsorption near-edge structure (XANES) showed that Zr occurred as zircon (ZrSiO4) in soils. The differences between the two methods were greater for Zr than for Cr. Zirconium concentrations obtained by EDXRF were higher than those by ICP-MS for all samples except three. The difference between the two methods was more pronounced in soils derived from granite that is widespread in western Japan. The EDXRF/ICP-MS ratios for seven soil samples from different horizons at a single sampling site ranged from 4.82 to 6.94 and were generally higher at the A horizon (Apg and Ag) and decreased with depth. Our results indicate that there is a high possibility of underestimation of Cr and Zr contents in soils for a considerable number of samples if determined with ICP-MS, and it could also overlook some important chemical characteristics of soils.

Determination of Sulfide and Total Sulfur in Ore by Wavelength-Dispersive X-ray Fluorescence

ABSTRACTThis paper describes the determination of total sulfur and sulfide in ore by X-ray fluorescence. The X-ray emission spectra of sulfur were measured by a wavelength-dispersive spectrometer. The samples were prepared as pressed powder pellets on boric acid substrates. The SKα1,2 line was used to determine total sulfur. The ratio between sulfide and total sulfur was measured by the ratio of satellite SKβ′ and SKβ1,3 line intensities. The total relative standard deviation (SD) of the measurements and preparation repeatability was less than 2%. Sample preparation was contributed to the error of the analysis. To determine total sulfur, the calibration curve was obtained from the samples of certified reference materials of gold-bearing sulfide-containing ore. The accuracy was verified by comparison with a gravimetric method. The relative SD was 6% for sulfur concentrations from 1 to 8 wt%. The calibration curve was defined using pure reagents to determine sulfide. The ore was analyzed by a gravimetric procedure with a relative SD of 6.5% for the sulfide concentration from 1 to 6 wt%.

In situ sulfur isotopes (δ34S and δ33S) analyses in sulfides and elemental sulfur using high sensitivity cones combined with the addition of nitrogen by laser ablation MC-ICP-MS

The sulfur isotope is an important geochemical tracer in diverse fields of geosciences. In this study, the effects of three different cone combinations with the addition of N2 on the performance of in situ S isotope analyses were investigated in detail. The signal intensities of S isotopes were improved by a factor of 2.3 and 3.6 using the X skimmer cone combined with the standard sample cone or the Jet sample cone, respectively, compared with the standard arrangement (H skimmer cone combined with the standard sample cone). This signal enhancement is important for the improvement of the precision and accuracy of in situ S isotope analysis at high spatial resolution. Different cone combinations have a significant effect on the mass bias and mass bias stability for S isotopes. Poor precisions of S isotope ratios were obtained using the Jet and X cones combination at their corresponding optimum makeup gas flow when using Ar plasma only. The addition of 4–8 ml min−1 nitrogen to the central gas flow in laser ablation MC-ICP-MS was found to significantly enlarge the mass bias stability zone at their corresponding optimum makeup gas flow in these three different cone combinations. The polyatomic interferences of OO, SH, OOH were also significantly reduced, and the interference free plateaus of sulfur isotopes became broader and flatter in the nitrogen mode (N2 = 4 ml min−1). However, the signal intensity of S was not increased by the addition of nitrogen in this study. The laser fluence and ablation mode had significant effects on sulfur isotope fractionation during the analysis of sulfides and elemental sulfur by laser ablation MC-ICP-MS. The matrix effect among different sulfides and elemental sulfur was observed, but could be significantly reduced by line scan ablation in preference to single spot ablation under the optimized fluence. It is recommended that the d90 values of the particles in pressed powder pellets for accurate and precise S isotope analysis should be less than 10 μm. Under the selected optimized analytical conditions, excellent agreements between the determined values and the reference values were achieved for the IAEA-S series standard reference materials and a set of six well-characterized, isotopic homogeneous sulfide standards (PPP-1, MoS2, MASS-1, P-GBW07267, P-GBW07268, P-GBW07270), validating the capability of the developed method for providing high-quality in situ S isotope data in sulfides and elemental sulfur.

Determination of halogen levels in marine geological samples

ABSTRACTA method for determining levels of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I) in marine geological samples using wavelength dispersive X-ray fluorescence is presented here. Samples are prepared as pressed powder pellets. The method makes full use of the advantages of the ability of the modern X-ray fluorescence spectrometer to detect ultra-light elements and high-powered X-rays. A series of calibration standards with an appropriate concentration range was developed using a standard addition method. Empirical coefficients were used to correct for matrix effects in the case of F and Cl, the rhodium Kα -Compton peak was used as internal standard for Br matrix corrections, and the rhodium Kb-Compton peak was used to correct for the matrix effect on I. For % concentration of the analyte, the precision (relative standard deviation) of the method was <5%. For concentrations <0.1%, the relative standard deviation depended heavily on the count rates (or concentration). The accuracy of the method was validated by comparison of the results to similar reference materials. The detection levels of this method (counting time100 s) were 100, 5, 0.5, and 10 µg g−1 for F, Cl, Br, and I, respectively. The method was here used to determine the levels of halogens in samples of 19 marine sediments (China, Russia, Canada, American), 10 marine manganese nodules (China, Russia, American, Germany, India, Japan), 4 cobalt-rich crust reference materials (Russia, China), reference materials, and 3 phosphorites.

Determination of tungsten in tantalum–tungsten alloy by X-ray fluorescence spectrometry using fusion, thin layer, and pressed powder pellet techniques

A method is described for the X-ray fluorescence (XRF) determination of tungsten in tantalum–tungsten alloy over the range of 10.5%–13.5%. The sample was prepared by three methods, namely, borate fusion, filter paper disk, and pressed powder pellet, respectively. We compared the feature of the three methods of specimen preparation and found that filter paper disk method was the most suitable technique for specimen preparation. Furthermore, the results were compared with those given by inductively coupled plasma optical emission spectrometry (ICP-OES), and the relative standard deviation was less than 2%, which could meet the requirement of this application.

The suppression of fluorescence peaks in energy-dispersive X-ray diffraction

A novel method to separate diffraction and fluorescence peaks in energy-dispersive X-ray diffraction (EDXRD) is described. By tuning the excitation energy of an X-ray tube source to just below an elemental absorption edge, the corresponding fluorescence peaks of that element are completely suppressed in the resulting spectrum. SinceBremsstrahlungphotons are present in the source spectrum up to the excitation energy, any diffraction peaks that lie at similar energies to the suppressed fluorescence peaks are uncovered. This technique is an alternative to the more usual method in EDXRD of altering the scattering angle in order to shift the energies of the diffraction peaks. However, in the back-reflection EDXRD technique [Hansford (2011).J. Appl. Cryst.44, 514–525] changing the scattering angle would lose the unique property of insensitivity to sample morphology and is therefore an unattractive option. The use of fluorescence suppression to reveal diffraction peaks is demonstrated experimentally by suppressing the Ca Kfluorescence peaks in the back-reflection EDXRD spectra of several limestones and dolomites. Three substantial benefits are derived: uncovering of diffraction peak(s) that are otherwise obscured by fluorescence; suppression of the Ca Kescape peaks; and an increase in the signal-to-background ratio. The improvement in the quality of the EDXRD spectrum allows the identification of a secondary mineral in the samples, where present. The results for a pressed-powder pellet of the geological standard JDo-1 (dolomite) show the presence of crystallite preferred orientation in this prepared sample. Preferred orientation is absent in several unprepared limestone and dolomite rock specimens, illustrating an advantage of the observation of rocks in their natural state enabled by back-reflection EDXRD.

Rapid Determination of Trace and Ultra Trace Level Elements in Diverse Silicate Rocks in Pressed Powder Pellet Targets by LA-ICP-MS using a Matrix-Independent Protocol

A simple, single sample preparation involving pressed rock powder pellets was utilised to determine the trace and ultra trace abundances of petrogenetically important elements including high field-strength elements and REEs by laser ablation-ICP-MS. One of the elements predetermined by XRF spectrometry served as an internal standard. The influence of sample preparation parameters (grain size, pellet compactness and amount of binding media) on analytical performance was also investigated, including sample homogeneity issues at the laser sampling scale. Line scanning with a high repetition frequency (20 Hz) and large beam diameter (200 μm) ensured ablation from a larger sample surface area, eliminating issues related to sample heterogeneity. A median grain size of about 10 μm for silicate rock powders was found to be sufficiently representative at this scale of laser sampling. Granitic rocks or samples containing resistant minerals such as zircon needed extra grinding to achieve grain sizes down to < 5 μm for better precision for elements that are concentrated in these phases. Using 137Ba as an internal standard, reasonable accuracies within 15–20% for most of the high mass trace elements were achieved; in the case of low mass elements, it may deviate up to 40%. Precision of measurements rarely exceeded 15% RSD. Une preparation simple d'echantillon individuel impliquant des pastilles de poudre de roche pressees a ete utilisee pour determiner les abondances en traces et ultra traces d'elements petrogenetiquement importants dont des «HFSE» et des «REE» par ablation laser-ICP-MS. L'un des elements predetermines par spectrometrie de fluorescence X a servi d'etalon interne. L'influence des parametres de preparation des echantillons (taille des grains, compacite des pastilles et quantite de liant) sur la performance analytique a egalement ete etudiee, y compris les questions d'homogeneite des echantillons a l'echelle d'echantillonnage du laser. Un balayage en ligne avec une frequence de repetition elevee (20 Hz) et un grand diametre de faisceau (200 μm) assure l'ablation d'une plus grande surface d'echantillon, ce qui elimine les problemes lies a l'heterogeneite de de ce dernier. Une taille moyenne de grain d'environ 10 μm pour les poudres de roches silicatees a ete juge suffisamment representative a cette echelle d'echantillonnage du laser. Les roches granitiques ou des echantillons contenant des mineraux resistants tels que le zircon necessitent un broyage supplementaire pour obtenir des tailles de grains plus petites, jusqu'a moins de 5 μm et ceci afin d'obtenir une meilleure precision pour les elements qui sont concentres dans ces phases. Avec le Ba137 utilise comme etalon interne, une precision raisonnable avec une marge d'erreur de 15 a 20% pour la plupart des elements-traces de masse eleves a ete atteinte, dans le cas d'elements de faible masse, l'erreur peut aller jusqu'a 40%. La precision des mesures a rarement depasse un ecart type relatif, «RSD», de 15%.

Electrical properties of multidoped ceria

Multidoped nanosized ceria powders were prepared by either modified glycine nitrate procedure (MGNP) or self-propagating reaction at room temperature (SPRT). As the dopants to CeO2, trivalent rare earth oxides such as Nd2O3, Sm2O3, Gd2O3, Dy2O3 and Y2O3 were used, with the total molar fraction of 20%. The pressed powder pellets were subjected to the densification by sintering at 1500°C, in an air atmosphere. A single-phase crystalline form was evidenced by X-ray diffractometry for both sintered materials. By means of complex impedance measurements, the conductivity of the sintered samples was determined as a function of temperature. At 700°C, the conductivity amounted to 2.19×10−2 and 1.40×10−2Ω−1cm−1 for the SPRT and for the MGNP sample, respectively. The corresponding values of activation energies of conductivity amounted to 0.72 (MGNP) and 0.59 (SPRT)eV in the temperature range 550–700°C.

Rapid Determination of Trace and Ultra-Trace Level Elements in Diverse Silicate Rocks in Pressed Powder Pellet Targets by LA-ICP-MS using a Matrix Independent Protocol

A simple, single sample preparation involving pressed rock powder pellets was utilised to determine the trace and ultra trace abundances of petrogenetically important elements including high field-strength elements and REEs by laser ablation-ICP-MS. One of the elements predetermined by XRF spectrometry served as an internal standard. The influence of sample preparation parameters (grain size, pellet compactness and amount of binding media) on analytical performance was also investigated, including sample homogeneity issues at the laser sampling scale. Line scanning with a high repetition frequency (20 Hz) and large beam diameter (200 μm) ensured ablation from a larger sample surface area, eliminating issues related to sample heterogeneity. A median grain size of about 10 μm for silicate rock powders was found to be sufficiently representative at this scale of laser sampling. Granitic rocks or samples containing resistant minerals such as zircon needed extra grinding to achieve grain sizes down to < 5 μm for better precision for elements that are concentrated in these phases. Using 137Ba as an internal standard, reasonable accuracies within 15–20% for most of the high mass trace elements were achieved; in the case of low mass elements, it may deviate up to 40%. Precision of measurements rarely exceeded 15% RSD. Une preparation simple d'echantillon individuel impliquant des pastilles de poudre de roche pressees a ete utilisee pour determiner les abondances en traces et ultra traces d'elements petrogenetiquement importants dont des «HFSE» et des «REE» par ablation laser-ICP-MS. L'un des elements predetermines par spectrometrie de fluorescence X a servi d'etalon interne. L'influence des parametres de preparation des echantillons (taille des grains, compacite des pastilles et quantite de liant) sur la performance analytique a egalement ete etudiee, y compris les questions d'homogeneite des echantillons a l'echelle d'echantillonnage du laser. Un balayage en ligne avec une frequence de repetition elevee (20 Hz) et un grand diametre de faisceau (200 μm) assure l'ablation d'une plus grande surface d'echantillon, ce qui elimine les problemes lies a l'heterogeneite de de ce dernier. Une taille moyenne de grain d'environ 10 μm pour les poudres de roches silicatees a ete juge suffisamment representative a cette echelle d'echantillonnage du laser. Les roches granitiques ou des echantillons contenant des mineraux resistants tels que le zircon necessitent un broyage supplementaire pour obtenir des tailles de grains plus petites, jusqu'a moins de 5 μm et ceci afin d'obtenir une meilleure precision pour les elements qui sont concentres dans ces phases. Avec le Ba137 utilise comme etalon interne, une precision raisonnable avec une marge d'erreur de 15 a 20% pour la plupart des elements-traces de masse eleves a ete atteinte, dans le cas d'elements de faible masse, l'erreur peut aller jusqu'a 40%. La precision des mesures a rarement depasse un ecart type relatif, «RSD», de 15%.

X-ray diffraction without sample preparation: Proof-of-principle experiments

The properties of a novel X-ray diffraction (XRD) technique having very low sensitivity to the sample morphology were previously elucidated through theoretical considerations and model simulations (Hansford, 2011 [1]). This technique opens up the possibility of mineralogical analysis by XRD without sample preparation. Here, the results of proof-of-principle experimental tests are presented. Two sets of experiments were performed using a vacuum chamber equipped with an X-ray tube source, sample holder and charge-coupled detector. Firstly, a pressed-powder pellet of α-quartz was placed in three different positions relative to the X-ray source and detector. The changes in position represent gross sample movements which would be inconceivable in conventional XRD analysis. The resulting back-reflection energy-dispersive spectra show a very high degree of correspondence other than an overall intensity factor dependent on the distance between the sample and detector. Secondly, the back-reflection spectrum of an unprepared limestone hand specimen, having mm-scale surface morphology, was compared to the spectrum of a calcite pressed-powder pellet. The correspondence of the diffraction peaks in the spectra demonstrate that the limestone is comprised dominantly of calcite. In both cases, the claims of the earlier paper are fully supported by the results of these experimental tests.

Simultaneous Determination of Major and Trace Elements in Fused Volcanic Rock Powders Using a Hermetic Vessel Heater and LA‐ICP‐MS

Fused glass prepared without the addition of a flux is generally more homogeneous than a pressed powder pellet and thus ideal for analysis of bulk samples by LA‐ICP‐MS. In this work, a new glass‐making method using a boron nitride crucible was developed to prepare homogenous glass samples from silicate rock powder. The apparatus consisted of a small boron nitride vessel with net volume of about 34 mm3 and two molybdenum strips. Applying the summed metal oxide normalisation technique, both major and trace element contents in the fused glass were measured by LA‐ICP‐MS. Analyses of five geochemical reference materials (spanning the compositional range basalt–andesite–rhyolite) indicated that the measured SiO2, Al2O3 and P2O5 contents matched the preferred values to within 5%, and the other major elements generally matched the preferred values to within 8%. Except for the transition metals, the measured trace element contents generally matched the preferred values to within 10%. Compared with the iridium heater method developed by Stoll et al. (2008), element volatilisation during high‐temperature melting was effectively suppressed in our method, but metal segregation caused by reduction of BN may cause loss of Cr, Ni and Cu. Although analysis with a large spot size has the advantage of improving counting statistics, matrix effects induced by mass loading of the ICP may hamper the accurate determination of some elements.

The quantification and application of handheld energy-dispersive x-ray fluorescence (ED-XRF) in mudrock chemostratigraphy and geochemistry

Traditionally, analytical techniques such as wavelength-dispersive x-ray fluorescence (WD-XRF), inductively-coupled plasma (ICP) and mass spectrometry (ICP-MS), instrumental neutron activation analysis (INAA), or stationary (bench-top) energy-dispersive x-ray fluorescence (ED-XRF) have been used to generate quantitative geochemical results. However, a more efficient means of data collection using portable ED-XRF instrumentation now allows the investigator to acquire rapid, non-destructive, quantitative measurements on drill core and clean, flat rock surfaces, in addition to pressed powder pellets typically used in WD-XRF analysis. Similar to traditional XRF methods, quantification using the handheld ED-XRF requires a matrix-specific calibration. Unfortunately, very few internationally-accepted mudrock or shale reference materials exist, and their elemental ranges provide inadequate coverage for the geochemical diversity of mudrocks. In order to return reliable, calibrated results, a unique set of reference materials has been developed that incorporates a wide range of mudrock elemental compositions. The current method provides elemental calibrations for major elements heavier than sodium, and the following trace elements: Ba, V, Cr, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Mo, Th, and U.A comparison of handheld energy-dispersive and wavelength-dispersive x-ray fluorescence (ED-XRF and WD-XRF) results from pressed powder pellets of Mississippian-age Barnett Shale of North-Central Texas, USA, is presented in order to evaluate the reliability of the reference calibration and the quantification of unknown samples using two different instrument platforms. It will be demonstrated that calibrated results from the handheld ED-XRF effectively define chemostratigraphic changes in real-time. As a consequence, quantified results can be used immediately to assess changes in bulk mineralogy, paleo-redox conditions, and to link down-core geochemical changes to stratigraphic, sedimentological, and paleoenvironmental observations.