High Analytical Precision Research Articles

NMR (1H and 13C) based signatures of abnormal choline metabolism in oral squamous cell carcinoma with no prominent Warburg effect

At functional levels, besides genes and proteins, changes in metabolome profiles are instructive for a biological system in health and disease including malignancy. It is understood that metabolomic alterations in association with proteomic and transcriptomic aberrations are very fundamental to unravel malignant micro-ambient criticality and oral cancer is no exception. Hence deciphering intricate dimensions of oral cancer metabolism may be contributory both for integrated appreciation of its pathogenesis and to identify any critical but yet unexplored dimension of this malignancy with high mortality rate. Although several methods do exist, NMR provides higher analytical precision in identification of cancer metabolomic signature. Present study explored abnormal signatures in choline metabolism in oral squamous cell carcinoma (OSCC) using 1H and 13C NMR analysis of serum. It has demonstrated down-regulation of choline with concomitant up-regulation of its break-down product in the form of trimethylamine N-oxide in OSCC compared to normal counterpart. Further, no significant change in lactate profile in OSCC possibly indicated that well-known Warburg effect was not a prominent phenomenon in such malignancy. Amongst other important metabolites, malonate has shown up-regulation but d-glucose, saturated fatty acids, acetate and threonine did not show any significant change. Analyzing these metabolomic findings present study proposed trimethyl amine N-oxide and malonate as important metabolic signature for oral cancer with no prominent Warburg effect.

A semi-automated system for quantifying the oxidative potential of ambient particles in aqueous extracts using the dithiothreitol (DTT) assay: results from the Southeastern Center for Air Pollution and Epidemiology (SCAPE)

Abstract. A variety of methods are used to measure the capability of particulate matter (PM) to catalytically generate reactive oxygen species (ROS) in vivo, also defined as the aerosol oxidative potential. A widely used measure of aerosol oxidative potential is the dithiothreitol (DTT) assay, which monitors the depletion of DTT (a surrogate for cellular antioxidants) as catalyzed by the redox-active species in PM. However, a major constraint in the routine use of the DTT assay for integrating it with large-scale health studies is its labor-intensive and time-consuming protocol. To specifically address this concern, we have developed a semi-automated system for quantifying the oxidative potential of aerosol liquid extracts using the DTT assay. The system, capable of unattended analysis at one sample per hour, has a high analytical precision (coefficient of variation of 15% for positive control, 4% for ambient samples) and reasonably low limit of detection (0.31 nmol min−1). Comparison of the automated approach with the manual method conducted on ambient samples yielded good agreement (slope = 1.08 ± 0.12, r2 = 0.92, N = 9). The system was utilized for the Southeastern Center for Air Pollution & Epidemiology (SCAPE) to generate an extensive data set on DTT activity of ambient particles collected from contrasting environments (urban, roadside, and rural) in the southeastern US. We find that water-soluble PM2.5 DTT activity on a per-air-volume basis was spatially uniform and often well correlated with PM2.5 mass (r = 0.49 to 0.88), suggesting regional sources contributing to the PM oxidative potential in the southeastern US. The correlation may also suggest a mechanistic explanation (oxidative stress) for observed PM2.5 mass-health associations. The heterogeneity in the intrinsic DTT activity (per-PM-mass basis) across seasons indicates variability in the DTT activity associated with aerosols from sources that vary with season. Although developed for the DTT assay, the instrument can also be used to determine oxidative potential with other acellular assays.

Improved precision and spatial resolution of sulfur isotope analysis using NanoSIMS

High precision analyses of all four sulfur isotopes in four pyrite and three sphalerite standards and in working reference samples were carried out using a CAMECA NanoSIMS 50L instrument. The measurements were made using three different settings of the Faraday cup (FC) and/or electron multiplier (EM) detectors, which meet different requirements for spatial resolution. The effects of EM aging and quasi-simultaneous arrival were corrected before the calibration of instrumental mass fractionation by a standard–sample–standard bracket method using the standards measured together with the samples. High analytical precision was achieved by counting 32S, 33S and 34S with the FCs and 36S with the EM (i.e. the FC–FC–FC–EM mode) using a 0.7 μm diameter ∼350 pA Cs+ primary beam and scanning over areas of 5 × 5 μm2. The standard deviations of spot-to-spot and grain-to-grain (external reproducibility 1 SD) measurements were less than 0.3, 0.3 and 0.7‰ for δ33S, δ34S and δ36S, respectively. To achieve a higher lateral resolution of ≤2 × 2 μm2, the Cs+ beam was reduced to 7–10 pA with a diameter of ∼200 nm; 32S was measured with the FC and the other signals were measured with the EMs. The external reproducibility (1 SD) was better than 0.5‰ for both δ33S and δ34S and was 3‰ for δ36S. To achieve the highest lateral resolution for the analysis of submicron-sized sulfides, a ∼0.7 pA Cs+ beam of ∼100 nm diameter was used, scanning over areas of 0.5 × 0.5 μm2, and all 32S, 33S and 34S were counted with the EMs. The external reproducibility (1 SD) was better than 1.5‰ for both δ33S and δ34S. These three modes have important applications in the isotope analysis of micron-sized sulfur samples, such as pyrite framboids and areas of complex zoning in sulfide minerals.

One-step kinetics-based immunoassay for the highly sensitive detection of C-reactive protein in less than 30 min

This article reveals a rapid sandwich enzyme-linked immunosorbent assay (ELISA) for the highly sensitive detection of human C-reactive protein (CRP) in less than 30min. It employs a one-step kinetics-based highly simplified and cost-effective sandwich ELISA procedure with minimal process steps. The procedure involves the formation of a sandwich immune complex on capture anti-human CRP antibody-bound Dynabeads in 15min, followed by two magnet-assisted washings and one enzymatic reaction. The developed sandwich ELISA detects CRP in the dynamic range of 0.3 to 81ngml−1 with a limit of detection of 0.4ngml−1 and an analytical sensitivity of 0.7ngml−1. It detects CRP spiked in diluted human whole blood and serum with high analytical precision, as confirmed by conventional sandwich ELISA. Moreover, the results of the developed ELISA for the determination of CRP in the ethylenediaminetetraacetic acid plasma samples of patients are in good agreement with those obtained by the conventional ELISA. The developed immunoassay has immense potential for the development of rapid and cost-effective in vitro diagnostic kits.

Abstract 18733: Evaluation of a Super-Sensitivity Cardiac Troponin I Assay for Diagnosing Non ST-Segment Elevation Myocardial Infarction

Introduction: Acute myocardial infarction (AMI) is defined by cardiac troponin (cTn) elevation. According to current guidelines the diagnosis of AMI requires a rise or fall of cTn (delta) with at least one value above the diagnostic cutoff, i.e. the 99th percentile (P99) of a reference population. Lately, cTn assays with high analytical precision have become available. Use of high-sensitivity cTn showed improved diagnostic accuracy with absolute deltas being superior compared to relative deltas. The diagnostic utility of super-sensitivity cTn assays, that are capable of cTn detection in >95% of the general population, has not been sufficiently elucidated. Hypothesis: We assessed the hypothesis that a super-sensitivity cTnI assay combined with a diagnostic algorithm that incorporates an absolute delta provides sufficient detection of non ST-segment elevation myocardial infarction (NSTEMI). Methods: The study comprised 1566 patients with new-onset chest pain (246 with NSTEMI, 222 with unstable angina pectoris, 1097 with non-coronary chest pain). On admission and 3 hours later cTnI was measured by a super-sensitivity assay (Erenna® cTnI immunoassay, Singulex, Inc., Alameda, CA, USA). Diagnostic performance was assessed via a two-step algorithm: First, 3h-cTnI had to exceed a certain cutoff concentration (P99 as well as arbitrarily chosen cTnI concentrations) and, when this criterion was fulfilled, secondly, an absolute delta criterion was applied. Results: A 3h-cTnI cutoff concentration of 40 ng/l provided a negative predictive value of 99.1% and a sensitivity of 95.5% indicating confident rule-out of NSTEMI, when this criterion was not fulfilled (n=1256). For patients with 3h-cTnI >40 ng/l (n=310) an absolute delta of ≥50 ng/l resulted in a positive predictive value, i.e. diagnostic certainty for ruling in NSTEMI, of 84.2%. Application of this algorithm to the overall study population yielded a negative predictive value of 96.1%, positive predictive value of 84.2%, sensitivity of 81.8% and a specificity of 97.1%. Conclusion: In conclusion, the super-sensitivity cTnI assay showed a clinically acceptable performance in diagnosing NSTEMI by use of an algorithm that is P99-independent and includes an absolute delta.

Using titanium-in-quartz geothermometry and geospeedometry to recover temperatures in the aureole of the Ballachulish Igneous Complex, NW Scotland

Abstract ‘Titanium-in-Quartz’ geothermometry suggests quartzites could yield reliable temperature estimates. We here apply four calibrations of the titanium-in-quartz geothermometer to contact-metamorphosed quartzites surrounding the Ballachulish Igneous Complex, Scotland. Two agree broadly with thermal modelling and pre-existing geothermometry; two give temperatures consistently too low. As reported in earlier studies, the technique suffers from difficulties in analysing low titanium (Ti) levels with high spatial and analytical precision. However, this study finds that the critical problem is one of Ti heterogeneity, which poses difficulties in constraining the chemical activity of Ti during quartz growth under metamorphic conditions. Scanning electron microscope-cathodoluminescence (SEM-CL) textures support an interpretation of extensive Ti disequilibrium despite the presence of rutile, indicating dynamic interplay between grain boundary diffusion, fluid/melt percolation and grain growth. The strong zonation suggests a possible geothermometer based on apparent volume diffusion of Ti-in-quartz to derive grain growth histories. Analysis of rutile–quartz interaction implies peak contact temperatures of 645±12 °C, precise but reliant on external estimates of cooling rate from thermal models. Our conclusions support caution in applying Ti-in-quartz geothermometry in aureole settings. However, rutile–quartz juxtaposition prior to heating to >600 °C defines a Ti diffusion couple, employable as a thermometer if cooling rates are constrained by other means.

A revised calibration of the clumped isotope thermometer

A growing number of materials and environmental settings are studied using the carbonate clumped isotope (Δ47) thermometer. The method has been applied in both biogenic and non-biogenic carbonate systems, in marine and terrestrial settings, over a wide range of geological timescales. The current Δ47 temperature calibration gives good temperature estimates for most biogenic materials, however, systematic biases are commonly observed at low temperatures.In this study we report additional calibration data, that covers a wider temperature range, at more evenly distributed temperatures, and are measured at higher analytical precision than the original calibration. Combining these data with the original calibration yields a Δ47–T relationship that is similar to the original calibration, though slightly less steep: Δ47=(0.0526±0.0025)×106/T2+(0.0520±0.0284). This revised calibration is in better agreement with biogenic carbonates, including those grown at low temperatures. The difference between the original and revised calibrations is significant for carbonates forming below 16 °C or above 49 °C (Δ47 values of 0.68‰ and 0.56‰). Additionally, we include a comprehensive analysis of the sources of error associated with Δ47 measurements and estimated temperatures and recommend measurement strategies for obtaining the desired precision.As an illustration, we apply the revised calibration and uncertainty analysis to 3 previously published studies. At low temperatures, the revised calibration results in significant differences from the original calibration and hence affects the interpretation of the environmental signal recorded. In light of our Δ47 errors analysis, in cases where the temperature signals are small, we find that replicate analyses are critical to identify a temperature signal.

High throughput method for Sr extraction from variable matrix waters and 87Sr/86Sr isotope analysis by MC-ICP-MS

Natural isotope tracers, such as strontium (Sr), can facilitate the tracking of brine migration caused by CO2 injection in carbon storage sites and assist in identifying the origin of formation waters associated with oil and gas exploration. However, it might be necessary to analyze tens of samples with complex chemical compositions over a short period to identify subsurface reactions and respond to unexpected fluid movement in the host formation. These conditions require streamlined Sr separation chemistry for samples ranging from pristine groundwaters to those containing high total dissolved solids, followed by rapid measurement of isotope ratios with high analytical precision. Here we describe a method useful for the separation of Sr from energy related geofluids and the rapid measurements of Sr isotopic ratios by MC-ICP-MS. Existing vacuum-assisted Sr separation procedures were modified by using inexpensive disposable parts that also eliminate cross contamination. These improvements will allow an operator to independently prepare samples for Sr isotope analysis using fast, low cost separation procedures and commercially available components. We optimized the elution chemistry by adjusting acid normality and elution rates to provide better separation of Sr from problematic matrices (e.g. Rb, Ca, Ba, K) associated with oilfield brines and formation waters. The separation procedure is designed for high sample throughputs that are ready for immediate Sr isotope measurements by MC-ICP-MS. Precise Sr isotope results can be achieved by MC-ICP-MS with a throughput of 4 to 5 samples per hour. Fluids from a range of geologic environments analyzed by this method yielded results within the analytical uncertainty of 87Sr/86Sr ratios previously determined by standard column separation and TIMS. This method provides a fast and effective way to use isolate Sr in a variety of geologic fluids for isotopic analysis by MC-ICP-MS.

Experimental calibration of Mg isotope fractionation between aragonite and seawater

The detectable magnesium (Mg) isotope fractionation between biogenic aragonite (including aragonitic corals, bivalves, scaphopod, and sclerosponges) and seawater can potentially be applied to reconstruct sea surface temperature (SST) in the past. To calibrate this thermometer, eight sets of inorganic precipitation experiments (‘free-drift’) in seawater (Mg/Ca=5 or 10) have been carried out at 25–55°C over a range of degassing rate. A cleaning procedure was adopted to remove Mg contamination by sea salt, surface absorbed Mg and silicate dust as nucleation centers. The Mg isotope fractionation between cleaned aragonite and seawater-like aqueous solution varies insignificantly with Mg/Ca ratios and Mg isotope compositions of the initial solution, and the CO2-degassing rate (0–75cc/min), but decreases noticeably with increasing temperatures having a temperature sensitivity of ∼0.008–0.01‰/°C in the following form: Δaragonite–Mg(aq)≈1000lnαaragonite–Mg(aq)=1.67(±0.36)-0.82(±0.11)×1000T where αaragonite-seawater is the fractionation factor, and T is the absolute temperature in Kelvin. It is consistent with equilibrium fractionation between Mg2+ aquo-complex and magnesite predicted by one theoretical calculation. Qualitative comparison among Mg-bearing carbonates based on Mg–O bond strengths show the relative sequence of 26Mg enrichment is aragonite>dolomite>magnesite>calcite. Thus, the surprising agreement indicates either the calculation overestimated Mg fractionation between magnesite and fluid, or both theoretical calculation and our calibration represent Mg isotope fractionation between MgCO30–H2O cluster and Mg2+ aquo complexes. Comparison of our calibration with the Mg isotope fractionation between biogenic aragonite and seawater suggests Mg and oxygen isotope fractionations of some biogenic aragonites (e.g., Porites sp. corals) agree with our calibration within analytical uncertainty, whereas others deviate significantly, indicating biological and/or kinetic isotope fractionation effects. Thus, although the precision of this temperature proxy is ∼±3–4°C (2σ) given our current analytical precision and temperature sensitivity of the calibration, several factors are limiting the application of this proxy to extract precise sea-surface temperatures (SSTs) from the biogenic aragonite, including the requirement for high analytical precision, proper sample cleaning procedures, uncertainty in δ26Mg values of seawater, and possible kinetic and/or biological isotope fractionation.

Reference Measurement Procedures for Alzheimer’s Disease Cerebrospinal Fluid Biomarkers: Definitions and Approaches With Focus on Amyloid β42

Cerebrospinal fluid (CSF) biomarkers for Alzheimer's disease (AD) are increasingly used in clinical settings, research and drug trials. However, their broad-scale use on different technology platforms is hampered by the lack of standardization at the level of sample handling, determination of concentrations of analytes and the absence of well-defined performance criteria for in vitro diagnostic or companion diagnostic assays, which influences the apparent concentration of the analytes measured and the subsequent interpretation of the data. There is a need for harmonization of CSF AD biomarker assays that can reliably, across centers, quantitate CSF biomarkers with high analytical precision, selectivity and stability over long time periods. In this position paper, we discuss reference procedures for the measurement of CSF AD biomarkers, especially amyloid β42 and tau. We describe possible technical approaches, focusing on a selected reaction monitoring mass spectrometry assay as a candidate reference method for quantification of CSF amyloid β42.

An update on in situ cosmogenic 14C analysis at ETH Zürich

We present the improved performance of the modified in situ cosmogenic 14C extraction system at ETH Zürich. Samples are now processed faster (2days in total) and are measured with a high analytical precision of usually <2% using the gas ion source of the MICADAS AMS facility. Measurements of the PP-4 standard sample show a good reproducibility and consistency with published values. Procedural blanks are very low at currently ∼4.0×10414C atoms. Analyses of samples from a ∼300year old rock avalanche prove that we can successfully apply in situ14C exposure dating to very young surfaces. Additionally, we present a modified calculation scheme for in situ14C concentrations which differs from that used for conventional radiocarbon dating. This new approach explicitly accounts for the characteristics of in situ14C production.

Standardisation of Rock–Eval pyrolysis for the analysis of recent sediments and soils

Rock–Eval 6 analysis, a well established screening tool for petroleum geochemistry, is being increasingly used to characterise the varying species of organic matter (OM) in the bulk samples of recent aquatic sediments. This is particularly important due to recent scientific attention on the role of OM in biogeochemical distribution of environmentally hazardous compounds (e.g., trace metals) in recent sediment archives. Rock–Eval’s automated use, low sample volume requirements and its high analytical accuracy and precision makes it an ideal tool for relatively rapid screening of OM in sediment cores. However, to date, there has been no broad scale standardisation to determine what may be contributing to each signal (e.g., S1,S2,S3,RC). We have selected a wide variety of representative, pure biochemicals (proteins, lipids, carbohydrates and lignins) and biological standards (phytoplankton, copepods, tree bark and conifer needles) to better understand the Rock–Eval 6’s measured organic matter parameters in the unconventional environmental samples. These data have been corroborated with organic petrographical and elemental (CHNS/O) data. Our results show that small organic molecules (<500Da) are largely responsible for the S1 hydrocarbon peak while lipids and aquatic biological standards are contributing most in the S2 signal, and in particular the more labile “S2a” signal. Furthermore, carbohydrates, lignins and terrigenous plant standards are most responsible for the S3 signal. We also note that the S3 signals (CO/CO2 ratios: OICO, OICO2 and OIRE6) are the best discriminants for the source of OM. Finally, step wise pyrolysis of biological standards coupled with elemental analysis (CHNS/O) suggests that S2 and, to a lesser extent, S3 (S3CO and/or S3CO2), would be most responsible for metal-binding elements such as S and N, with implications for element biogeochemical cycles.

Implications of ferrous and ferric iron in antigorite

Microprobe analyses of antigorite show that (Al+Cr) and inferred Fe 3+ correlate inversely with Si apfu in a Tschermaks substitution. This observation suggests that the uptake of Fe 3+ is not simply related to f O 2 . For Si = 1.95 apfu estimated Fe 3+ = 0.032 apfu (or 0.95 wt% Fe 2 O 3 ). Such estimates of Fe 3+ require high analytical accuracy and precision, and assume a fixed polysomatic formula (e.g., m = 17) and freedom from interlayer sheet-silicate impurities. In many cases the estimates appear to be high. An alternative measure of Fe 3+ is provided by the partitioning of total Fe and Mg between antigorite and olivine in well-equilibrated natural antigorite-olivine-magnetite parageneses. Extrapolation of Nernst and Roozeboom partition plots to Fe-free olivine permits an estimate of the Fe 3+ content of the average antigorite in this paragenesis, namely 0.42 or 0.64 wt% Fe 2 O 3 . The partition estimates are in good agreement with the results of Mossbauer spectroscopy performed here on 14 antigorites from metaperidotites, together with four from the literature. These spectra reveal a range of 0.16 to 1.94 in wt% Fe 2 O 3 in metaperidotite antigorite, with an average of 0.83. In two olivine-bearing rocks, antigorite has Fe 3+ /∑Fe ratios of 0.13 and 0.15, which corresponds to wt% Fe 2 O 3 = 0.47 and 0.54, respectively. Larger amounts of Fe 2 O 3 occur in some, but not all, vein antigorites. The prograde formation of antigorite in serpentinite from lizardite is accompanied by loss of some cronstedtite component and the precipitation of additional magnetite. The Roozeboom Mg/Fe partition plot is concave down rather than up; in other words the partition coefficient K D is a function of the X Mg of olivine. This behavior has been found in other olivine-mineral pairs. It can be interpreted to reflect strongly non-ideal solution behavior of MgFe-olivine at low temperatures, viz. W G ≈ 8.5 kJ assuming a symmetrical solution. MgFe-brucite appears to be similarly non-ideal.

Calculation of river-seawater endmembers and differential trace metal scavenging in the Columbia River plume

A simple model is presented for calculating river and seawater mixing zone endmembers. This model allows construction of a conservative mixing line with respect to trace metals scavenged from surface waters, in the absence of direct endmember sampling. Results of the model suggest a transition from non-conservative to conservative behavior of the trace metals gallium (Ga) and zirconium (Zr) along a transect extending offshore of the Columbia River, indicating environmental controls on differential scavenging. Mechanistic explanation of observed differential scavenging is supported by wind data indicating northward transport of Columbia River plume waters, followed by southwest, offshore, transport. Columbia River plume waters transported to the southwest at the time of sample collection were therefore flanked offshore by aged plume waters returning from the north. While upwelling conditions provide nutrients during southerly transport of plume waters, northward plume transport is associated with downwelling, low nutrient conditions. Low phytoplankton abundance during periods of northward plume transport reduces trace metal scavenging, therefore dilution of river waters with ocean surface waters of comparatively low Ga and Zr concentrations results in near-conservative mixing of Ga and Zr in offshore, aged, plume waters. Results of this work suggest dynamic modification of trace metal residence time within close geographic proximity established by physical and biologic controls, dictated by local winds. Lower trace metal scavenging rates, resulting in a longer residence time, are suggested during northward transport of Columbia River plume waters, compared to higher scavenging rates, and thus shorter residence times, during southerly transport of plume waters. Gallium, demonstrating high analytical precision, reduced contamination risk, and decreased complications of upwelled sources relative to Zr, is proposed to provide identification of aged Columbia River plume waters.

Quantifying Peptides in Complex Mixtures with High Sensitivity and Precision Using Targeted Approach with a Hybrid Linear Ion Trap Orbitrap Mass Spectrometer

High‐resolution, accurate‐mass (HR/AM) mass spectrometry is routinely used for identification and relative quantitation of peptides present in complex mixtures using stable‐isotope labeling, isobaric tags, or label‐free techniques. However, HR/AM application for targeted peptide analysis is less explored. Due to the complexity of biological samples, accurate mass and retention time alone are not sufficient for verifying identity of a targeted peptide. Therefore, sequence confirmation via MS/MS is essential during the early verification and validation stages of development of a targeted quantitative assay. Here, a workflow was developed for targeted protein/peptide quantitation on the LTQ Orbitrap Velos to use high resolution selected ion monitoring (SIM) for quantitation followed by targeted MS/MS for sequence confirmation. A standard peptide mixture spiked into a yeast digest mixture at different concentration as quantitative targets and LOD was as low as 10 amol. An additional yeast digest was used to further evaluate the precision and throughput and the workflow by 77 peptides (25 yeast proteins). All the peptides were successfully quantified and verified with high analytical precision in a single LC/MS run.

Fast single piece identification with a 3D scanning LIBS for aluminium cast and wrought alloys recycling

In industrial recycling processes secondary metals need to be separated by material grades before they can be further processed. The identification and separation into different material classes lead to higher value-added industrial feedstock and prevent downgrading processes. Secondary raw materials can be used more efficiently resulting in an increased use of waste products in resource-intensive production processes. Laser-induced breakdown spectroscopy (LIBS) offers a contact free, multi-elemental and fast method for the inline quantitative analysis of single objects in moving particle streams. The LIBS method presented in this paper is based on a 3D object detection combined with a scanning LIBS setup. The optical system consists of a pulsed Nd:YAG laser running at 40 Hz, delivering a 200 mJ double pulse for plasma generation. A high performance three axis galvo-scanner guides the laser beam onto single pieces moving at 3 m s−1 through a measuring volume of 600 × 600 × 100 mm3 with a precision of ±1.5 mm. Twenty channels of a high resolution Paschen–Runge spectrometer are simultaneously processed within a few microseconds enabling multi-elemental analysis of different aluminium (Al) alloys. A dimensionless figure of merit is introduced for the evaluation of the analytical performance. Sorting measurements of Al post-consumer scrap charges, consisting of wrought and cast alloys were carried out. After discarding 20% of the data as outliers low and high silicon alloyed Al pieces were identified with a correctness of >96%. In a second sorting scenario the analytical discrimination of 8 different Al alloys of production scrap, requiring high analytical precision, is investigated. A mean identification correctness of wrought Al alloys >95% is demonstrated successfully for the first time.

Determination of the composition of Co–Pt thin films with quantitative electron-probe microanalysis

Quantitative electron-probe microanalysis (EPMA) with energy-dispersive (EDS) and wavelength-dispersive (WDS) X-ray spectroscopy was performed to determine the chemical composition of Co–Pt ferromagnetic thin films. The conventional “bulk” EPMA approach was applied and tested in detail by using several analytical set-ups with different combinations of Co and Pt spectral lines, beam energies and quantitative matrix-correction programs. The analyses with dedicated, thin-film EPMA programs were also made for comparison. The results were critically examined in order to assess their reliability and accuracy. The commonly used EDS analyses showed significant scatter between the set-ups and generally suffered from a poor analytical sensitivity. In contrast, the quantitative WDS analyses were fully consistent and practically independent of the analytical set-up. With the optimized WDS a high analytical precision, an improved sensitivity and an ultimate quantitative accuracy of better than 1% relative were achieved. The results confirmed that by using WDS microanalysis at low beam energies and by measuring the low-energy Co–Lα and Pt–Mα X-rays we were able to obtain the most accurate and reliable, quantitative, compositional analyses of Co–Pt thin films with thicknesses down to ≈ 100 nm.

Negative ion source for chlorine isotope ratio measurements

A negative chlorine ion source has been designed and constructed. The source utilizes direct surface ionization of chloromethane gas on a hot metal filament. Four different alloys for the filament material were tested: W99Th1, W75Re25, Hf97.5Zr2.5 and Mo52.5Re47.5. We conclude that the best filament material is the MoRe alloy, for which the signal-to-noise ratio is optimal. The ion source is used for chlorine isotope ratio measurements with higher precision and sensitivity than the positive ionization source used previously. Inasmuch as only negative ions of the two isotopes of interest are observed, no corrections to the measured isotope ratio are necessary, and less rigously purified samples may be analyzed. The negative ion currents are considerably larger than positive ion currents obtained with an electron ionization source. This implies higher analytical precision (typically 0.005 permil) and sensitivity.

Oxygen Isotopes in Mantle and Crustal Magmas as Revealed by Single Crystal Analysis

Oxygen is the most abundant element in the Earth’s crust, mantle, and fluids and therefore its isotopic composition provides robust constraints on magma genesis. Application of oxygen isotope geochemistry to volcanology and igneous petrology provides a much needed foundation for radiogenic isotope and trace element approaches. Since isotope fractionations at high temperature are small, there is a demand for high analytical precision in order to recognize and interpret small (tenths of permil) variations in isotopic composition. Recently improved analytical techniques involving lasers and ion microprobes, and reduction in sample and spot size, has painted a picture of isotope complexity on a single crystal scale that is helpful in interpreting magma genesis and evolution. In this chapter a review is provided for several classic examples of silicic and basic magmatism, including Yellowstone and Iceland, that shows isotope zoning and heterogeneity reaching several permil. Isotope heterogeneity fingerprints crystal sources and provides constraints on diffusive and recrystallizational timescales. These new lines of evidence reveal that magma genesis happens rapidly, at shallow depths, and through batch assembly processes. Oxygen isotope geochemistry spans more than 50 years of investigation and is the most developed among other traditional (e.g., C, N, H, S, Li, B) and less-traditional (e.g., Fe, Mo, Cu) stable isotope systems. While we provide basic concepts of isotope fractionation below, the reader is referred to three prior RiMG volumes on stable isotopes (Valley, Taylor, and O’Neil 1986 – volume 16; Valley and Cole 2001 – volume 43; Johnson et al. 2004 – volume 55), and the Hoefs (2005) and Sharp (2006) textbooks for greater treatment and historic perspective. Finally this Chapter does not deal with oxygen isotopic variations in meteorites and planetary igneous materials, and interested readers are referred to RiMG volume 68, “Oxygen in the Solar System” (MacPherson et al. 2008). …

Two-dimensional pH distributions and dynamics in bioturbated marine sediments

The seafloor is the site of intense biogeochemical and mineral dissolution–precipitation reactions which generate strong gradients in pH near the sediment-overlying water interface. These gradients are usually measured in one-dimension vertically with depth. Two-dimensional pH distributions in marine sediments were examined at high resolution (65 × 65 μm pixel) and analytical precision over areas of ∼150 to 225 cm 2 using a newly developed pH planar fluorosensor. Dramatic three-dimensional gradients, complex heterogeneity, and dynamic changes of pH occur in the surficial zone of deposits inhabited by macrofauna. pH can vary by ±2 units horizontally as well as vertically over millimeter scales. pH minima zones often form in association with redoxclines within a few millimeters of inner burrow walls, and become more pronounced with time if burrows remain stable and irrigated for extended periods. Microenvironmental pH minima also form locally around decaying biomass and relict burrow tracks, and dissipate with time (∼5 d). H + concentrations and fluxes in sandy mud show complex acid–base reaction distributions with net H + fluxes around burrows up to ∼12 nmol cm −2 d −1 and maximum net reaction rates varying between −90 (consumption) to 120 (production) μM d −1 (∼90 nmol cm −1 d −1 burrow length). Acid producing zones that surround irrigated burrows are largely balanced by acid titration zones along inner burrow walls and outer radial boundaries. The geometry and scaling of pH microenvironments are functions of diagenetic reaction rates and three-dimensional transport patterns determined by sediment properties, such as diffusive tortuosity, and by benthic community characteristics such as the abundance, mobility, and size of infauna. Previously, undocumented biogeochemical phenomena such as low pH regions associated with in-filled relict biogenic structures and burrowing tracks are readily demonstrated by two-dimensional and time-dependent images of pH and sedimentary structure.