Applied Geochemistry (v.21, #5)

Frontiers in Analytical Geochemistry – An IGC 2004 perspective by Russell Harmon; Riccardo Vannucci (727-729).

Laser-induced breakdown spectroscopy – An emerging chemical sensor technology for real-time field-portable, geochemical, mineralogical, and environmental applications by Russell S. Harmon; Frank C. DeLucia; Catherine E. McManus; Nancy J. McMillan; Thomas F. Jenkins; Marianne E. Walsh; Andrzej Miziolek (730-747).
Laser induced breakdown spectroscopy (LIBS) is a simple spark spectrochemical sensor technology in which a laser beam is directed at a sample surface to create a high-temperature microplasma and a detector used to collect the spectrum of light emission and record its intensity at specific wavelengths. LIBS is an emerging chemical sensor technology undergoing rapid advancement in instrumentation capability and in areas of application. Attributes of a LIBS sensor system include: (i) small size and weight; (ii) technologically mature, inherently rugged, and affordable components; (iii) real-time response; (iv) in situ analysis with no sample preparation required; (v) a high sensitivity to low atomic weight elements which are difficult to determine by other field-portable sensor techniques, and (vi) point sensing or standoff detection. Recent developments in broadband LIBS provide the capability for detection at very high resolution (0.1 nm) of all elements in any unknown target material because all chemical elements emit in the 200–980 nm spectral region. This progress portends a unique potential for the development of a rugged and reliable field-portable chemical sensor that has the potential to be utilized in variety of geochemical, mineralogical, and environmental applications.

Double pulse, calibration-free laser-induced breakdown spectroscopy: A new technique for in situ standard-less analysis of polluted soils by Michela Corsi; Gabriele Cristoforetti; Montserrat Hidalgo; Stefano Legnaioli; Vincenzo Palleschi; Azenio Salvetti; Elisabetta Tognoni; Chiara Vallebona (748-755).
Laser-induced breakdown spectroscopy (LIBS) is a promising technique for in situ environmental analysis. The potential of this technique for accurate quantitative analysis could be greatly improved using an innovative experimental setup – based on the use of two laser pulses suitably retarded – and analyzing the results with a standard-less procedure which overcomes the problems related to matrix effects. A new mobile instrument for soil analysis, developed at the Applied Laser Spectroscopy Laboratory in Pisa, is presented, and some experimental results are given.

The continuous flow elemental analyzer-isotopic ratio mass spectrometer (EA-IRMS) technique provides a significant improvement over conventional extraction methods for the determination of C- and S-isotope ratios in geological materials. It is faster and requires much smaller quantities of material for analysis. Sample preparation is simple, with little or no need for chemical or complete mechanical mineral phase separation, and EA-IRMS sample introduction is rapid. However, because of its simplicity and the fact that data quality depends on the control of a variety of factors, the technique requires rigid adherence to a careful sample analysis protocol.The matching of sample and reference peak heights by sample weight adjustment minimizes non-linearity effects. An accurate calibration should be determined by using standards having a wide range of isotopic compositions, ideally bracketing the samples analysed to both low and high isotopic ratios, and a regular analysis of standards undertaken to maintain the accuracy of the calibration. The calibration equation must be monitored throughout the run by regular analysis of standards, and performance of the Cu-reduction reactor regularly checked to avoid O2 saturation. With this level of attention to analytical detail, measured precision on replicates of isotopic standards is in the order of ±0.1‰ for both C and S isotopic analyses. For S this is a significant improvement over conventional techniques, with 53% of natural samples analysed replicating to better than ±0.1‰.

Compound-specific chlorine isotope ratios of TCE, PCE and DCE isomers by direct injection using CF-IRMS by Orfan Shouakar-Stash; Robert J. Drimmie; Min Zhang; Shaun K. Frape (766-781).
A method for determining compound-specific Cl isotopic compositions (δ 37Cl) was developed for tetrachloroethene (PCE), trichloroethene (TCE), cis-dichloroethene (cis-DCE), trans-dichloroethene (trans-DCE) and 1,1-dichloroethene (1,1-DCE). The isotope ratio mass spectrometry (IRMS) used in this study has nine collectors, including two for m/z 50 and 52 (CH3Cl) and two for m/z 94 and 96 (CH3Br). The development of this method is based on the fact that fragments with mass ratios of 94/96, 95/97 and 96/98 are produced from PCE, TCE and DCE isomers during ion bombardment in the source of a mass spectrometer. Using continuous flow isotope ratio mass spectrometry coupled with gas chromatography (GC–CF-IRMS), it is possible to separate these compounds on-line and directly measure the Cl isotopic ratios of the fragments with the specific mass ratios.Both pure phase and aqueous samples were used for Cl isotopic analysis. For pure phase samples, a vapour phase of the chlorinated ethenes was injected directly into the GC, whereas the solid phase micro extraction (SPME) method was used to extract these compounds from aqueous solutions. The precisions of this analytical technique were ±0.12‰ (1σ, n  = 30), ±0.06‰ (1σ, n  = 30), and ±0.08‰ (1σ, n  = 15) for PCE, TCE and DCE isomers, respectively. The limits of quantification (LOQ) for analyzing Cl isotopic composition in aqueous solutions were 20, 5, and 5 μg/L for PCE, TCE and DCE isomers, respectively. This corresponds to 6–9 nano-mole of Cl, which is approximately 80 times lower than the most sensitive existing method. Compared to methods previously available, this new development offers the following advantages: (1) The much lower LOQ make it possible to extract these compounds directly from aqueous solutions using SPME without pre-concentration; (2) The linking of a GC with an IRMS eliminates off-line separation; and (3) Because the fragments used for isotopic ratio measurement are produced during ion bombardment in the mass spectrometer, there is no need to convert chlorinated ethenes to methyl chloride. As a result, this technique greatly enhances the efficiency for isotopic analysis by eliminating procedures for pre-concentration, off-line separation and sample preparation. In addition, it also reduces the potential for isotopic fractionation introduced during these procedures.Compound-specific Cl stable isotope analysis can be used as a tool to study the sources of organic contaminants in groundwater and their behaviour in the subsurface environments. It may also assist in understanding processes such as transport, mixing, and degradation reactions.

In situ sulfur isotope analysis by laser ablation MC-ICPMS by Chris Bendall; Yann Lahaye; Jens Fiebig; Stefan Weyer; Gerhard Peter Brey (782-787).
A new method for in situ S isotopic analysis was tested using a laser ablation system together with a multi-collector (MC)-ICPMS. The method was tested for the analysis of pyrite, pyrrhotite, chalcopyrite and pentlandite using a large pyrite crystal as an in-house standard. Repeated measurements of Py, Pn, Po and Cpy provide an average internal precision of less than 0.1‰ (2σ). The method was also applied to a pyrite-bearing orogenic Au deposit to display the ability of the method to resolve minor variations in δ 34S across growth zoning in pyrite.

Laser ablation multicollector ICPMS determination of δ 11B in geological samples by Massimo Tiepolo; Claudia Bouman; Riccardo Vannucci; Johannes Schwieters (788-801).
A method for the in situ single spot δ 11B characterisation of geological materials with laser ablation multicollector ICP mass spectrometry (LA-MC-ICPMS) has been developed. The mass spectrometer was equipped with both Faradays and multiple ion counters. Four samples with different B contents (12–31,400 ppm) and isotopic compositions (δ 11B are between −8.71 and +13.6‰) were analysed. Samples include the B4 tourmaline and 3 MPI-DING glasses (StHs6/80-G, GOR132-G and GOR128-G).All sources of B isotopic fractionation during the analysis (mass bias, laser-induced isotopic fractionation and detector efficiency drift) have been evaluated and quantified. Instrumental mass bias is the major source of fractionation, altering the original isotopic ratio up to 13%. Fractionation related to laser sampling and transport to the ICP was found to be very low (less than 0.0015% s−1). Fractionation effects due to drift in ion counter efficiencies were found to be significant. Nevertheless, the “standard-sample-standard” bracketing approach could be used to correct for the above fractionation effects using NIST SRM 610 as external standard.With spot sizes of 60–80 μm in diameter, geologically meaningful results can be achieved on samples containing at least 10 ppm B, i.e., results with precisions that can discriminate between the different reservoirs on Earth. Data obtained with Faraday detectors on NIST SRM 610 and B4 tourmaline show high precision (down to 0.04‰, 1σ) and accuracy. Boron isotope ratios measured in the glass samples using multiple ion counting show significantly higher standard deviations (up to 2.5‰, 1σ), but they are very close to the values that can be expected from counting statistics. No significant variations with spot size or B contents were observed. Most of the values are within 1σ level of the reference values.The developed method was applied to a series of ashes from Mt. Etna erupted in 1995 having B contents between 14 and 20 ppm. The B isotope compositions of the ashes are between −4.8 and −10.7‰, with a weighted average value of −8.0 ± 1.9‰ (1σ).

Influence of composition and thermal history of volcanic glasses on water content as determined by micro-Raman spectrometry by A. Di Muro; D. Giordano; B. Villemant; G. Montagnac; B. Scaillet; C. Romano (802-812).
Development of Raman spectrometry for quantification of water content in natural glasses requires the assessment of the dependence of the technique on glass composition and thermal history. In the low frequency domain, Raman spectra topology varies due to glass depolymerization and substitution in the framework of (Si4+)IV by alkali-balanced (Al3+)IV and (Fe3+)IV in calcalkaline (rhyolite to basaltic andesite) and alkaline (trachyte, phonolite to alkali basalt) glasses. These processes result in strong dependence of previous analytical procedure (internal calibration) on glass composition. Here, we show that an analytical procedure based on calibration to an external standard is only faintly composition-dependent for Si-rich alkaline glasses (trachytes–phonolites). For a given glass composition, thermal history also plays a fundamental role in the choice of Raman procedure for water analysis. Repeated cycles of thermal annealing induce microcrystallization of hydrous trachyte glasses and modify cation distribution in the glass structure. Application of these concepts to analysis of banded obsidians suggests that small-scale heterogeneities in glasses are not simply related to magma degassing, but could depend on thermal history and consequent relaxation paths in the melt.
Keywords: Raman; Glasses; Alkaline magmas; Volatiles; Water; Obsidian; Viscous dissipation;

Combined investigations of fluid inclusions in opaque ore minerals by NIR/SWIR microscopy and microthermometry and synchrotron radiation X-ray fluorescence by Francisco Javier Rios; James V. Alves; Carlos A. Pérez; Éden C. Costa; Carlos A. Rosière; Kazuo Fuzikawa; José M. Correia Neves; Alexandre de O. Chaves; Sônia P. Prates; Raul E. de Barrio (813-819).
An alternative IR microscopy system in the NIR (near infrared, up to 10 μm) and SWIR (short wavelength infrared, up to 1.4 μm) ranges has been developed for the study of opaque ore minerals. The system uses either IR LED or IR light bulb sources depending on the degree of opacity of the investigated minerals. This paper presents the methodology and the promising results obtained in studies of opaque ore minerals such as Ag minerals (pyrargyrite) from epithermal deposits and Nb-tantalates (columbite) from pegmatites. It also presents results on the internal features of hematites from Fe ore banded formations and tungstates from granite–greenstone belt deposits. The data obtained on fluid inclusions from pyrargyrite and hematite crystals have been integrated by complementary information from X-ray fluorescence analysis using synchrotron radiation (μ-SXRF) under conditions specifically designed for the study of opaque ore minerals.

Determination and significance of the Mn(II) Zero-Field Splitting (ZFS) interaction in the geochemistry of travertines by G. Montegrossi; F. Di Benedetto; A. Minissale; M. Paladini; L.A. Pardi; M. Romanelli; F. Romei (820-825).
An analytical approach, based on the electron paramagnetic resonance (EPR) spectroscopy of Mn(II) in travertines, has been developed in order to obtain relevant information about the local inhomogeneity of calcite and about the thermodynamic conditions which control the formation of travertine deposits. This information is crucial to constrain the precipitation of travertine under different geochemical contexts. An empirical correlation between the spectral features and the zero-field splitting (ZFS) interaction has been established through numerical simulations of EPR spectra. The variability of the investigated parameters and the applicability of the method have been tested on several travertines from Central Italy.

Recent progress in X-ray CT as a geosciences tool by V. Cnudde; B. Masschaele; M. Dierick; J. Vlassenbroeck; L. Van Hoorebeke; P. Jacobs (826-832).
For many years X-ray computed tomography has been widely used as a medical diagnostical tool. This non-destructive technique was soon found to be very useful in rock material research. In the 1970s CT was introduced in material research while in the 1990s, micro-CT became an important non-destructive research technique. Presently nano-CT is being developed creating even more possibilities for the 3D visualization of small objects. In this paper CT, micro-CT and nano-CT are specified and discussed. Several applications illustrate the possibilities, specific advantages and limitations of each instrument. As with every technique some restrictions occur, but X-ray CT is found to be an emerging non-destructive analytical technique with many possibilities in material research.

A new low-interference characterization method for hydrocarbons occluded inside asphaltene structures by Zewen Liao; Alain Graciaa; Ansong Geng; Anna Chrostowska; Patrice Creux (833-838).
Some hydrocarbons occluded inside asphaltene structures can be considered to be “original oil”, and are very important especially for severely post-altered crude oil in related geochemical studies such as oil/oil, oil/source correlation. The use of oxidising reagents could properly release these occluded hydrocarbons, and make possible direct study of these compounds without interference from the segments chemically bonded to the asphaltene molecule. Interference from adsorbed and/or co-precipitated compounds can be avoided by applying an asphaltene purification procedure.

Direct quantification of rare earth element concentrations in natural waters by ICP-MS by Michael G. Lawrence; Alan Greig; Kenneth D. Collerson; Balz S. Kamber (839-848).
A direct quadrupole ICP-MS technique has been developed for the analysis of the rare earth elements and yttrium in natural waters. The method has been validated by comparison of the results obtained for the river water reference material SLRS-4 with literature values. The detection limit of the technique was investigated by analysis of serial dilutions of SLRS-4 and revealed that single elements can be quantified at single-digit fg/g concentrations. A coherent normalised rare earth pattern was retained at concentrations two orders of magnitude below natural concentrations for SLRS-4, demonstrating the excellent inter-element accuracy and precision of the method. The technique was applied to the analysis of a diluted mid-salinity estuarine sample, which also displayed a coherent normalised rare earth element pattern, yielding the expected distinctive marine characteristics.

A new, rapid and reliable method for the determination of reduced sulphur (S2−) species in natural water discharges by Giordano Montegrossi; Franco Tassi; Orlando Vaselli; Eva Bidini; Angelo Minissale (849-857).
The determination of reduced S species in natural waters is particularly difficult due to their high instability and chemical and physical interferences in the current analytical methods. In this paper a new, rapid and reliable analytical procedure is presented, named the Cd–IC method, for their determination as ΣS2− via oxidation to SO 4 2 - after chemical trapping with an ammonia–cadmium solution that allows precipitation of all the reduced S species as CdS. The S2−–SO4 is analysed by ion-chromatography. The main advantages of this method are: low cost, high stability of CdS precipitate, absence of interferences, low detection limit (0.01 mg/L as SO4 for 10 mL of water) and low analytical error (about 5%). The proposed method has been applied to more than 100 water samples from different natural systems (water discharges and cold wells from volcanic and geothermal areas, crater lakes) in central-southern Italy.