Marcel Guillong

MPI‐DING reference glasses for in situ microanalysis: New reference values for element concentrations and isotope ratios

We present new analytical data of major and trace elements for the geological MPI-DING glasses KL2-G, ML3B-G, StHs6/80-G, GOR128-G, GOR132-G, BM90/21-G, T1-G, and ATHO-G. Different analytical methods were used to obtain a large spectrum of major and trace element data, in particular, EPMA, SIMS, LA-ICPMS, and isotope dilution by TIMS and ICPMS. Altogether, more than 60 qualified geochemical laboratories worldwide contributed to the analyses, allowing us to present new reference and information values and their uncertainties (at 95% confidence level) for up to 74 elements. We complied with the recommendations for the certification of geological reference materials by the International Association of Geoanalysts (IAG). The reference values were derived from the results of 16 independent techniques, including definitive (isotope dilution) and comparative bulk (e.g., INAA, ICPMS, SSMS) and microanalytical (e.g., LA-ICPMS, SIMS, EPMA) methods. Agreement between two or more independent methods and the use of definitive methods provided traceability to the fullest extent possible. We also present new and recently published data for the isotopic compositions of H, B, Li, O, Ca, Sr, Nd, Hf, and Pb. The results were mainly obtained by high-precision bulk techniques, such as TIMS and MC-ICPMS. In addition, LA-ICPMS and SIMS isotope data of B, Li, and Pb are presented.

Quantitative multi-element analysis of minerals, fluid and melt inclusions by laser-ablation inductively-coupled-plasma mass-spectrometry

Laser-ablation ICPMS has become widely accessible as a powerful and efficient multi-element microanalytical technique. One of its key strengths is the ability to analyse a wide concentration range from major (tens of wt.%) to trace (ng/g) levels in minerals and their microscopic inclusions. An ArF excimer laser system (λ = 193 nm) with imaging optics for controlled UV ablation and simultaneous petrographic viewing was designed specifically for representative sampling and quantitative multi-element analysis of microscopic fluid, melt and mineral inclusions beneath the sample surface. After a review of the requirements and recent technical developments, results are presented which together document the reliability and reproducibility of quantitative microanalysis of complex samples such as zoned crystals or fluid and melt inclusions in various host minerals. Analytical errors due to elemental fractionation are reduced to the typical precision achieved by quadrupole LA-ICPMS in multi-element mode (2–5% RSD). This progress is largely due to the small size of aerosol particles generated by the optimized UV optical system. Depth profiling yields representative and accurate concentration results at a resolution of ∼0.1 μm perpendicular to the ablation surface. Ablation is largely matrix-insensitive for different elements, such that silicate and borate glasses, silicates and oxide minerals, or direct liquid ablation can be used interchangeably for external standardization of any homogeneous or heterogeneous material. The absolute ablation rate is material dependent, however, so that quantitative LA-ICPMS analysis requires an internal standard (i.e., an independent constraint such as the absolute concentration of one element). Our approach to quantifying fluid and melt inclusion compositions is described in detail. Experiments with synthetic fluid inclusions show that accurate results are obtained by combining the LA-ICPMS analysis of element concentration ratios with a microthermometric measurement of the NaCl equivalent concentration and an empirical description of the effect of major cations on the final melting temperatures of ice, hydrohalite or halite. Expected calibration errors for NaCl-H2O-dominated fluids are smaller than the typical analytical scatter within an assemblage of simultaneously trapped fluid inclusions. Analytical precision is limited by representative ablation of all phases in heterogeneous inclusions and the integration of transient ICPMS signals, to typically ±10 to 20% RSD. Element concentrations in devitrified and even coarsely crystallized silicate melt inclusions can be reconstituted from LA-ICPMS signals. Deconvolution of inclusion and host signals with internal standardization automatically corrects for sidewall crystallization after melt entrapment at high temperature. A test using melt inclusions in a midocean ridge basalt, a summary of published geochemical studies and a new application to REE analysis of coexisting fluids and mineral phases in carbonatite-related veins illustrate the versatility and some of the strengths and limitations of LA-ICPMS, in comparison with other microanalytical techniques.

Effect of particle size distribution on ICP-induced elemental fractionation in laser ablation-inductively coupled plasma-mass spectrometry

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) has become one of the well-accepted analytical techniques for in situ trace element analysis and a large number of successful applications have shown its potential. Each commonly employed laser wavelength (1064, 266, 213, 193, 157 nm) leads to some degree of non-stoichiometric ablation, which makes quantification using non-matrix-matched calibration standards difficult for some elements. Time-dependent changes in elemental ratios (so-called elemental fractionation) have been ascribed mostly to processes occurring at the ablation site. Therefore, wavelengths and related irradiance are the major variables that have been used to study this phenomenon in detail. However, there are a large number of parameters that influence the ablation process, aerosol transport, and the excitation process within the ICP. Each process can contribute to elemental fractionation, making the effects of each difficult to separate and to study in detail. The influence of the ICP as one possible source has not been studied thoroughly. The aim of this study was the determination of the source of elemental fractionation using a 266 nm Nd∶YAG laser ablation system. The sample transport system was designed to keep gas flows and plasma conditions constant. Various ablation procedures (single hole drilling and scanning) were tested to investigate the influence of the particle size on the excitation process within the ICP. Mineral wool was used to filter various fractions of the laser-induced aerosol to study signal behaviour as a function of the mass load of the ICP. Uranium and thorium, two elements with very similar properties (ionisation potential and concentration) in the NIST 600 Glass standard series, were used in particular to study ICP processes. It is shown that the particle size distribution is dependent on the wavelength of the laser and the absorption behaviour of the sample. The 266 nm Nd∶YAG laser produces a particle size distribution which is significantly larger in comparison with aerosols produced using a laser wavelength of 193 nm. Signals related to the ablated volume show that the larger particle fractions are not completely vaporised and ionised in the ICP. Filtering certain particle fractions allows final stoichiometric excitation and ionisation, but is accompanied by a loss of 50–80% of the total signal. For single hole ablation, the particle size distribution becomes smaller with increasing depth of the crater. Therefore, scanning mode ablation (which takes place always at the surface) produces a constant supply of larger particles, which results in significantly higher matrix effects within the ICP, as shown by significant changes in the elemental ratio of U∶Th. These studies indicate that the secondary effect of incomplete aerosol or particle excitation within the ICP is the dominant process influencing elemental fractionation during LA-ICP-MS. The effect was observed to be different for individual ICP sources and, therefore, the requirement for matrix-matched quantification in LA-ICP-MS remains instrument-dependent.

A comparison of 266 nm, 213 nm and 193 nm produced from a single solid state Nd:YAG laser for laser ablation ICP-MS

Laser ablation using wavelengths of 266 nm, 213 nm and 193 nm as a sampling method for ICP-MS was compared. Unlike previous studies, this was performed under essentially identical laser ablation conditions with the exception of wavelength. This was achieved by using a single solid state laser source (1064 nm Nd:YAG) for harmonic generation together with sum frequency mixing and optical parametric oscillation. Experiments were carried out on the NIST 600 series silicate glasses. Particle size distributions for all three wavelength were measured and increased in the order 193 nm 150 nm are produced in comparison to longer wavelengths when ablating with 193 nm. Due to the decreased amount of particles above 0.15 µm vaporisation induced elemental fractionation within the ICP, especially for more transparent samples is reduced. Data on the behaviour of 213 nm ablation and resulting ICP-MS response demonstrated that this wavelength is intermediate between 193 nm and 266 nm, but biased towards 193 nm for more opaque samples and biased towards 266 nm for those more transparent. This study (maintaining laser parameter constant and not exceeding depth to diameter ratios of 2∶1) shows that the wavelengths in first instance are responsible for particle size distribution and that their distribution leads to enhanced vaporisation, atomisation and ionisation effects within the ICP. Until now, only 193 nm produced particle sizes (as shown for the selection of silicate samples) can be stoichiometrically converted into ions using common ICP-MS instruments.

Sensitivity enhancement in laser ablation ICP-MS using small amounts of hydrogen in the carrier gas

The addition of 4–9 ml min−1 of hydrogen to the helium carrier gas flow in 193 nm excimer laser ablation increases the sensitivity for most of 47 investigated elements by a factor of 2–4. The sensitivity enhancement for some elements, including beryllium, phosphorus, arsenic, platinum and gold, is even 5–7 fold. This effect can be explained by a higher electron temperature in the plasma. A correlation exists between the enhancement factor and the 1st ionization energy. Limits of detection are improved for all elements except those with hydrogen based polyatomic interferences, such as silicon, potassium, calcium and selenium, thus opening up new applications in LA-ICP-MS. A similar but weaker effect was found for the addition of methane; almost no sensitivity enhancement was found for nitrogen addition.

Application of a particle separation device to reduce inductively coupled plasma-enhanced elemental fractionation in laser ablation- inductively coupled plasma-mass spectrometry

The particle size distribution of laser ablation aerosols are a function of the wavelength, the energy density and the pulse duration of the laser, as well as the sample matrix and the gas environment. Further the size of the particles affects the vaporization and ionization efficiency in the inductively coupled plasma (ICP). Some matrices produce large particles, which are not completely vaporized and ionized in the ICP. The previous work has shown that analytical results such as matrix-independent calibration, accuracy and precision can be significantly influenced by the particle sizes of the particles. To minimize the particle size related incomplete conversion of the sample to ions in the ICP a particle separation device was developed, which allows effective particle separation using centrifugal forces in a thin coiled tube. In this device, the particle cut-off size is varied by changing the number of turns in the coil, as well as by changing the gas flow and the tube diameter. The interaction of the laser with the different samples leads to varying particle size distributions. When carrying out quantitative analysis with non-matrix matched calibration reference materials, it was shown that different particle cut-off sizes were required depending on the ICP conditions and the instrument used for analysis. Various sample materials were investigated in this study to demonstrate the applicability of the device. For silicate matrices, the capability of the ICP to produce ions was significantly reduced for particles larger than 0.5 mm, and was dependent on the element monitored. To reduce memory effects caused by the separated particles, a washout procedure was developed, which additionally allowed the analysis of the trapped particles. These results clearly demonstrate the very important particle size dependent ICP- MS signal response and the potential of the described particle size based separator for the reduction of ICP induced elemental fractionation. 2002 Elsevier Science B.V. All rights reserved.

Quasi ‘non-destructive’ laser ablation-inductively coupled plasma-mass spectrometry fingerprinting of sapphires

Abstract A homogenized 193 nm excimer laser with a flat-top beam profile was used to study the capabilities of LA-ICP-MS for ‘quasi’ non-destructive fingerprinting and sourcing of sapphires from different locations. Sapphires contain 97–99% of Al 2 O 3 (corundum), with the remainder composed of several trace elements, which can be used to distinguish the origin of these gemstones. The ablation behavior of sapphires, as well as the minimum quantity of sample removal that is required to determine these trace elements, was investigated. The optimum ablation conditions were a fluency of 6 J cm −2 , a crater diameter of 120 μm, and a laser repetition rate of 10 Hz. The optimum time for the ablation was determined to be 2 s, equivalent to 20 laser pulses. The mean sample removal was 60 nm per pulse (approx. 3 ng per pulse). This allowed satisfactory trace element determination, and was found to cause the minimum amount of damage, while allowing for the fingerprinting of sapphires. More than 40 isotopes were measured using different spatial resolutions (20–120 μm) and eight elements were reproducibly detected in 25 sapphire samples from five different locations. The reproducibility of the trace element distribution is limited by the heterogeneity of the sample. The mean of five or more replicate analyses per sample was used. Calibration was carried out using NIST 612 glass reference material as external standard. The linear dynamic range of the ICP-MS (nine orders of magnitude) allowed the use of Al, the major element in sapphire, as an internal standard. The limits of detection for most of the light elements were in the μg g −1 range and were better for heavier elements (mass >85), being in the 0.1 μg g −1 range. The accuracy of the determinations was demonstrated by comparison with XRF analyses of the same set of samples. Using the quantitative analyses obtained using LA-ICP-MS, natural sapphires from five different origins were statistically classified using ternary plots and principal multi-component analysis.

Determination of sulfur in fluid inclusions by laser ablation ICP-MS

The quantification capabilities for sulfur microanalysis in quartz-hosted fluid inclusions were investigated with laser ablation (LA) inductively coupled plasma quadrupole mass spectrometry (ICP-Q-MS) and ICP sector field mass spectrometry (ICP-SF-MS) allowing resolution of sulfur from polyatomic interferences. A scapolite mineral sample was used to determine the sulfur concentration in NIST SRM 610 (570 ± 70 µg g−1), which was further validated using EPMA and then used as standard reference material for the fluid inclusion analysis. The sulfur concentration in an assemblage of brine inclusions from a quartz–molybdenum vein was determined to be 5900 ± 2000 µg g−1 measuring 17 inclusions with the ICP-SF-MS and 13 inclusions with the ICP-Q-MS instrument. The agreement between the two ICP-MS instruments for sulfur was ∼5% and well within the overall precision of 35% relative standard deviation. The precision and accuracy was not limited by interferences, but by a so far unknown sulfur contamination source when ablating the host mineral quartz. Due to this contamination, a careful baseline correction is necessary which is described and discussed in detail. Nevertheless, the method developed to determine sulfur maintains the multi-element capabilities for individual fluid inclusions. Limits of detection for sulfur are correlated with the inclusion mass and were found to be ∼ 30–100 µg g−1 for 60 μm inclusions.

LA-ICP-MS Pb–U dating of young zircons from the Kos–Nisyros volcanic centre, SE Aegean arc

Zircon Pb–U dating has become a key technique for answering many important questions in geosciences. This paper describes a new LA-ICP-MS approach. We show, using previously dated samples of a large quaternary rhyolitic eruption in the Kos–Nisyros volcanic centre (the 161 ka Kos Plateau Tuff), that the precision of our LA-ICP-MS method is as good as via SHRIMP, while ID-TIMS measurements confirm the accuracy. Gradational age distribution over >140 ka of the Kos zircons and the near-absence of inherited cores indicate near-continuous crystallisation in a growing magma reservoir with little input from wall rocks. Previously undated silicic eruptions from Nisyros volcano (Lower Pumice, Nikia Flow, Upper Pumice), which are stratigraphically constrained to have happened after the Kos Plateau Tuff, are dated to be younger than respectively 124 ± 35 ka, 111 ± 42 ka and 70 ± 24 ka. Samples younger than 1 Ma were corrected for initial thorium disequilibrium using a new formula that also accounts for disequilibrium in 230Th decay.

The zircon ‘matrix effect’: evidence for an ablation rate control on the accuracy of U–Pb age determinations by LA-ICP-MS

Many studies now acknowledge the occurrence of systematic discrepancies between U–Pb ages determined in zircons in situ by LA-ICP-MS and the benchmark analytical method ID-TIMS. In this study, we present detailed investigations into the ablation characteristics of zircons that suggest an underlying mechanism responsible for these age biases relative to ID-TIMS. Confocal laser scanning microscopy of laser ablation pits reveals that there are small but significant differences in the amount of material removed by the laser between different zircons. Based on numerous pit depth and LA-ICP-MS 206Pb/238U ratio measurements of a suite of natural zircon reference materials and samples, we demonstrate that a systematic age bias is strongly correlated with the offset in ablation rates between the primary reference material and sample zircons. We offer further insights concerning the effects of thermal annealing on the ablation behaviour of zircons and demonstrate that, although there is a change in laser ablation rates for annealed zircons, the variations between different zircons are not eliminated. Finally, we show that slight variations in laser focus also influence the ablation behaviour of zircons and may further degrade the accuracy of U–Pb age determinations.