Result 1 - 10 of total 336
Elements
Impressive Analytical Tools
2018
| Language | English |
|---|---|
| Publishing country | de |
| Document type | Article ; Online |
| Database | BASE - Bielefeld Academic Search Engine (life sciences selection) |
Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.
Geochemical Perspectives Letters
2024
Abstract: Ferropericlase (Mg,Fe)O is after bridgmanite the most abundant phase in the lower mantle. The ultralow velocity zones above the core-mantle boundary may contain very Fe-rich magnesiowüstite (Fe,Mg)O, possibly as result of the fractional crystallisation ... ...
| Abstract | Ferropericlase (Mg,Fe)O is after bridgmanite the most abundant phase in the lower mantle. The ultralow velocity zones above the core-mantle boundary may contain very Fe-rich magnesiowüstite (Fe,Mg)O, possibly as result of the fractional crystallisation of a basal magma ocean. We have experimentally studied the solubility of nitrogen in the ferropericlase-magnesiowüstite solid solution series as function of iron content. Multi-anvil experiments were performed at 20–33 GPa and 1600–1800 °C in equilibrium with Fe metal. Nitrogen solubility increases from a few tens ppm (μg/g) for Mg-rich ferropericlase to more than 10 wt. % for nearly pure wüstite. Such high solubilities appear to be due to solid solution with NiAs-type FeN. Our data suggest that during fractional crystallisation of a magma ocean, the core-mantle boundary would have become extremely enriched with nitrogen, such that the deep mantle today could be the largest nitrogen reservoir on Earth. The often discussed “subchondritic N/C” ratio of the bulk silicate Earth may be an artefact of insufficient sampling of this deep reservoir. |
|---|---|
| Subject code | 550 |
| Language | English |
| Publishing country | de |
| Document type | Article ; Online |
| Database | BASE - Bielefeld Academic Search Engine (life sciences selection) |
Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.
Fisheries Management and Ecology
Consequences for estimation of growth and reference points in northern pike (Esox lucius)
2024
Abstract: Accurate age estimates are crucial for assessing the life-histories of fish and providing management advice, but validation studies are rare for many species. We corroborated age estimates with annual cycles of oxygen isotopes (δ18O) in otoliths of 86 ... ...
| Abstract | Accurate age estimates are crucial for assessing the life-histories of fish and providing management advice, but validation studies are rare for many species. We corroborated age estimates with annual cycles of oxygen isotopes (δ18O) in otoliths of 86 northern pike (Esox lucius) from the southern Baltic Sea, compared results with visual age estimates from scales and otoliths, and assessed bias introduced by different age-estimation structures on von Bertalanffy growth models and age-structured population models. Age estimates from otoliths were accurate, while age estimates from scales significantly underestimated the age of pike older than 6 years compared to the corroborated reference age. Asymptotic length () was larger, and the growth coefficient was lower for scale ages than for corroborated age and otolith age estimates. Consequentially, scale-informed population models overestimated maximum sustainable yield (), biomass at (), relative frequency of trophy fish (), and optimal minimum length limit but underestimated fishing mortality at (). Using scale-based ages to inform management regulations for pike may therefore result in conservative management and lost yield. The overestimated asymptotic length may instill unrealistic expectations of trophy potential in recreational anglers targeting large pike, while the overestimation in MSY would cause unrealistic expectations of yield potential in commercial fishers. |
|---|---|
| Subject code | 333 |
| Language | English |
| Publishing country | de |
| Document type | Article ; Online |
| Database | BASE - Bielefeld Academic Search Engine (life sciences selection) |
Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.
Geochimica et Cosmochimica Acta
2024
Abstract: Bones and teeth are often the only fossil remains of vertebrates that are preserved over geological time in sedimentary rocks. They render valuable archives for geochemical proxies which are commonly used for paleo-reconstructions. However, the ... ...
| Abstract | Bones and teeth are often the only fossil remains of vertebrates that are preserved over geological time in sedimentary rocks. They render valuable archives for geochemical proxies which are commonly used for paleo-reconstructions. However, the fossilization mechanisms of bone are not yet well understood. Crucial processes are the transformation of bioapatite and the replacement of collagen by thermodynamically more stable apatite phases, such as fluorapatite. In the present study, aqueous alteration experiments on cortical bone samples were performed under simulated early diagenetic conditions in order to investigate whether and how an external PO4 source affects post mortem bone mineralization. Additionally, abiotic oxygen isotope exchange mechanisms between bioapatite and aqueous solutions were assessed by using either 18O-enriched water or phosphate as a tracer. The presence of an external sedimentary 18O-labeled PO4 source led to a rapid formation of new fluorapatite crystallites at the sample’s margin that was highly enriched in 18O. Meanwhile, in the interior of the samples carbonate-poor HAp formed through a dissolution-precipitation process without incorporating any of the 18O tracer. These two processes appear to act independently from each other. In samples exposed to 18O-labeled aqueous solutions lacking a PO4 source, no newly grown apatite crystallites were found, however in the interior of these samples, nano-crystalline carbonate-poor or -free hydroxylapatite precipitated. A comparatively low but uniform 18O-enrichment was measured from the sample’s margin towards its interior, which is assumed to have resulted from the adsorption of H218O onto crystallite surface sites and collagen. Overall, our results suggest that a fast incorporation of 18O-doped PO4 from the sediment source accelerated bone mineralization and consequently changed the oxygen isotope composition of the PO4 group in the bone mineral phase more rapidly and to a greater extent than in a diagenetic setting lacking additional ... |
|---|---|
| Subject code | 550 |
| Language | English |
| Publishing country | de |
| Document type | Article ; Online |
| Database | BASE - Bielefeld Academic Search Engine (life sciences selection) |
Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.
Geostandards and Geoanalytical Research
The F, Cl, Br and I Contents of Reference Glasses BHVO-2G, BIR-1G, BCR-2G, GSD-1G, GSE-1G, NIST SRM 610 and NIST SRM 612 by Marks et al . This Issue
2017
| Publishing country | de |
|---|---|
| Document type | Article ; Online |
| Database | BASE - Bielefeld Academic Search Engine (life sciences selection) |
Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.
Elements
Knowing how far you can trust your data
2017
| Publishing country | de |
|---|---|
| Document type | Article ; Online |
| Database | BASE - Bielefeld Academic Search Engine (life sciences selection) |
Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.
Elements
Time-of-flight Mass Spectrometry: A New Tool for Laser Ablation Analyses
2016
Abstract: I have worked in the field of mass spectrometry for some 30 years now, and I have long been interested in tracking those technical developments that might offer new options for the analytical geochemist. When laser ablation was selected as the topic for ... ...
| Abstract | I have worked in the field of mass spectrometry for some 30 years now, and I have long been interested in tracking those technical developments that might offer new options for the analytical geochemist. When laser ablation was selected as the topic for the October 2016 issue of Elements I wanted to devote this Toolkit contribution to some emerging technology that might signifi cantly advance mass spectrometry’s contribution to laser ablation analyses. After a bit of research, and having contacted some of the leading names in the field of laser ablation, I chose to highlight the time-of-flight (TOF) method as a new analytical strategy with promising new opportunities. There are a variety of strategies for separating an ion beam into its individual components. Perhaps the most well-known method involves passing ions through a perpendicular magnetic field, causing the beam to be deflected at a right angle to the magnetic field lines. The amount of deflection is dependent upon the momentum:charge ratio of a given ion; in the case where all components in the ion beam have the same, or very similar, kinetic energies, the radius of curvature becomes a function of the mass of any given ion. A second common strategy involves passing the ion beam down the central axis of a quadrupole mass filter, which is basically four parallel rods to which time-varying voltages are applied (FIG. 1). Only those ions with the selected mass:charge ratio will travel through this filter, all other ions will be removed from the ion beam. Quadrupole systems can rapidly change the mass:charge ratio that is transmitted; a limitation is that one must select which elements will be investigated in advance of a given analysis. Unfortunately, should one wish to analyze the contributions of, say, 20 different elements in a complex ion beam, then the average detection time for any single element will be less than 5% of the total analysis time – with 95% of the ions for that species being “wasted” during those periods when other ion species are being observed. Particularly problematical is when components of the ion beam are highly transient, such that the composition of the ion beam changes over the course of the few hundred milliseconds that one might need for a single sweep of the selected mass sequence. When measuring the aerosol particles generated by a laser ablation system, it is exactly such transient signals that are provided. In contrast to the two techniques above, time-of-flight (TOF) mass spectrometry works on a completely different principle. If an ion has a known energy, usually that provided by the voltage potential between the ion source and the mass spectrometer, then the time needed for the ion to cover a known distance can be used to identify its mass. For common types of such laboratory instrumentation, a flight distance up to a few meters is the general rule, with travel times commonly in the range of a few to a few 10s of microns. In order to determine the time required to cover the given distance, one obviously needs to know both the start and end times for each and every ion being analyzed, and these values need to be known with excellent precision. The end signal is typically defined by the arrival time of the ion at the detector – modern detectors can routinely operate in the low-nanosecond performance range. The start time, on the other hand, is commonly defined by the pulsing of the ion extraction voltage. This strategy is beset by the problem that the voltage responsible for injecting ions into a TOF mass spectrometer can be active only during a brief time window. The system must then be switched off to allow the heaviest ions in the system to travel to the detector, otherwise the light elements (e.g. hydrogen) from a subsequent pulse might overtake the heavy species (e.g. uranium) injected during the preceding extraction pulse. This was a shortcoming of early TOF systems: they typically spent most of their time in a passive mode waiting for ions to be cleared from the system. It was not uncommon that for early systems to spend 99% of the time in passive mode, waiting for ions to finish traversing the TOF segment, resulting in slow rates of data collection. On the other hand, the TOF method has the major advantage of detecting all (or nearly all) ion species, without the need to preselect which elements are of interest. Furthermore, detection is effectively simultaneous, meaning that even transient signals lasting <10 milliseconds cannot “sneak through” undetected, regardless of which element one is investigating. So what does this all have to do with laser ablation? With its transient signals and with the common desire to quantify the abundances of all possible elements, TOF mass spectrometry has some very attractive features for the laser ablation community. For this reason, I contacted the company TOFWERK AG, (based in Thun, Switzerland). Founded in 2002, TOFWERK is one of a very small number of instrument manufacturers combining inductively coupled plasma (ICP) ion sources with TOF technology. Importantly, over the past few years, quantitative results have begun to appear in the scientific literature [Tanner and Günther (2008) being among the first], providing a picture of what this technology can really achieve. In 2012, TOFWERK produced a complete prototype instrument for performance testing, going on to market their icp TOF instrument to the scientific community in 2014 (F IG. 2). This system is built around a modified Thermo Fisher ICP-quadrupole instrument where the exiting quadrupole mass filter has been replaced by an ion transport segment followed by a TOF mass filter plus ion detection system. Importantly, the TOF part of the system has been designed and is being built in-house at TOFWERK, meaning that the ion optics are fully optimized for the properties of the ICP ion source. The icp TOF system is marketed as a stand-alone mass spectrometer, where the customer has many options for purchasing the “laser + optics + ablation cell” from third party vendors. TOFWERK has employed a well-known, but nonetheless elegant, geometry to improve the ion throughput of their instrument, namely the use of an orthogonal ion acceleration cell for their TOF segment(FIG. 3). This arrangement, now widely used by many TOF systems, allows the plasma ion source to operate continuously, injecting a non-pulsed ion beam into the injection zone of the TOF mass filter [see review by Guilhaus et al. (2000)]. It is actually the injection voltage within the TOF segment that is modulated, typically operating at a frequency of 33 kHz, equivalent to a cycle time of only 30 μs. TOFWERK has not disclosed the pulse width for the injection of ions into the drift sector, but I could imagine this to be on the order of 30 ns or perhaps less. If my “guestimate” is correct, then the system would have a duty cycle of only 0.1% (i.e. 30 ns/30 μs). This is where the orthogonal geometry comes into play. During the vast remainder of the 30 μs cycle, when ions are not being injected into the time-of-flight drift zone, ions continue to be delivered to the TOF injection zone where they become available for the next extraction pulse. In other words, the orthogonal geometry acts much like an ion storage device, greatly helping to improve the sensitivity of the system. Importantly, this system still delivers good mass resolving power of ~3,000 (TOFWERK 2016), which would be sufficient to split the difference in mass between, for example, 56 Fe+ (mass 55.9349 Daltons) and the molecular interference 40 Ca 16O+ (55.9575 Daltons), supposing that any CaO+ molecule survived passage through the up-stream collision cell. This mass resolution is superior to that provided by most quadrupole systems. Now, I would like to turn my attention to two specific examples of laser ablation inductively coupled time-of-flight mass spectrometry (LA–ICP–TOF–MS) from the geochemical literature. The first application I highlight is the use of TOF technology for the generation of element distribution maps. Gundlach-Graham and Günther (2016) compared the performance of quadrupole and TOF systems, where the simultaneous multi-element acquisition capability of their TOF system was coupled with a low volume ablation cell providing a washout time – the time needed to flush all ablated sample particle from the ablation cell – of only circa 10 ms. In contrast, their quadrupole system operated with a more conventional large-format ablation cell providing a washout time of ~500 ms, necessitated by the requirement of the mass spectrometer to operate in peak jumping mode. Gundlach-Graham and Günther (2016) report that imaging using a TOF system was ~1,800 times faster than the established methodology based on a quadrupole mass spectrometer. On the other hand, Gundlach-Graham and Günther (2016) report that when using a 1 μm diameter laser spot, they could achieve a detection limit of ~100 μg/g for their TOF system, whereas the quadrupole system managed a better detection limit of ~8 μg/g, but only for a single isotope. The second application I want to highlight is the use of laser ablation technology for quantifying trace element abundances in natural fluid inclusions (see also Wagner et al. 2016 this issue). In this case, one of the largest technological challenges is the inherently transient signals that are generated when the wall of a fluid inclusion is initially breeched. Harlaux et al. (2015) compared three differing mass spectrometer classes: a quadrupole system, a sector field system – both these being peak-hopping systems – and a TOF spectrometer system from TOFWERK. The same laser system was used in all three cases but, with respect to the ablation cell, the two peak-hopping technologies employed large cylindrical cells whereas the TOF experiments were based on a low dispersion (small volume) cell so as to take advantage of the quasi-simultaneous acquisition capability of a TOF detector. The conclusion of these authors is that, of the three technologies, the sector field instrument provides the best limits of detection. However, thanks to the short 30 μs cycling time of the TOF system and the better signal: noise ratio provided by the small geometry ablation cell, TOF technology provided the best overall analytical uncertainties. So what does the future hold? It will take another couple of years to have a clear picture of LA–ICP–TOF–MS technology’s relative strengths and limitations. More information is needed especially in terms of TOF performance with regards to trace element quantification. However, based on current information, the future looks bright. I think scientists considering the purchase of laser ablation trace element instrumentation would be well served to investigate the TOF alternative in more detail. As for myself, having worked for three decades in the field of isotopic microanalysis, I am eager to know how the icp TOF tool performs for isotopic and U–Th–Pb dating. |
|---|---|
| Subject code | 530 |
| Publishing country | de |
| Document type | Article ; Online |
| Database | BASE - Bielefeld Academic Search Engine (life sciences selection) |
Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.
Elements
2016
| Publishing country | de |
|---|---|
| Document type | Article ; Online |
| Database | BASE - Bielefeld Academic Search Engine (life sciences selection) |
Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.
Program with Abstracts
A weak link in solid state microanalysis
2015
Abstract: The isotopic signatures of natural solid materials can record a wealth of information about the geological, biological or environmental processes that were active during a sample’s genesis. However, a major technical challenge is that such archives are ... ...
| Abstract | The isotopic signatures of natural solid materials can record a wealth of information about the geological, biological or environmental processes that were active during a sample’s genesis. However, a major technical challenge is that such archives are frequently heterogeneous in their isotopic signatures at the microscopic scale. Often such information can be recovered only by analytical methods working at nanogram or smaller sampling scales. Modern Secondary Ion Mass Spectrometers (SIMS) provide analytical repeatabilities substantially better than ± 0.2 ‰ (1sd) for major element isotope ratio determinations while employing test portion masses as low as 150 picograms. Further advantages of SIMS are its speed (typically a few minutes per result) and that sample preparation only involves the production of a well polished sample surface. Current SIMS instrumentation has now reached a maturity such that overall analytical uncertainties in isotopic determinations are dominated by the quality of the RMs used for calibration and quality control purposes. In reality, analysts often resort to isotope RMs that have not been evaluated even at the microgram scale. Furthermore, the absence of common calibration materials prevents any meaningful traceability assessment between laboratories. The lack of suitable RMs for isotopic determinations is a severe research impediment in analytical geochemistry the use of non-suitable calibration materials can have serious implications in such fields as climate research (e.g., oxygen isotopes), natural resource evaluation (e.g., sulphur isotopes) and deep Earth petrology (e.g., carbon isotopes). |
|---|---|
| Subject code | 550 |
| Publishing country | de |
| Document type | Conference proceedings ; Online |
| Database | BASE - Bielefeld Academic Search Engine (life sciences selection) |
Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.
Contributions to Mineralogy and Petrology
2022
Abstract: The solubility of N2 in basaltic (MORB) and haplogranitic melts was studied at oxidizing conditions (oxygen fugacity about two log units above the Ni–NiO buffer). Under these conditions, N2 is expected to be the only significant nitrogen species present ... ...
| Abstract | The solubility of N2 in basaltic (MORB) and haplogranitic melts was studied at oxidizing conditions (oxygen fugacity about two log units above the Ni–NiO buffer). Under these conditions, N2 is expected to be the only significant nitrogen species present in the melt. Experiments were carried out from 0.1 to 2 GPa and 1000–1450 ˚C using either an externally heated TZM pressure vessel, an internally heated gas pressure vessel or a piston cylinder apparatus. Nitrogen contents in run product glasses were quantified by SIMS (secondary ion mass spectrometry). To discriminate against atmospheric contamination, 15N-enriched AgN3 was used as the nitrogen source in the experiments. According to infrared and Raman spectra, run product glasses contain N2 as their only dissolved nitrogen species. Due to interactions with the matrix, the N2 molecule becomes slightly infrared active. Nitrogen solubility in the melts increases linearly with pressure over the entire range studied; the effect of temperature on solubility is small. The data may, therefore, be described by simple Henry constants Khaplogranite = (1461 ± 26) ppm N2/GPa and KMORB = (449 ± 21) ppm N2/GPa, recalculated to ppm by weight (μg/g) of isotopically normal samples. These equations describe the solubility of nitrogen during MORB generation and during melting in the crust, as we show by thermodynamic analysis that N2 is the only significant nitrogen species in these environments. Nitrogen solubility in the haplogranitic melt is about three times larger than for the MORB melt, as is expected from ionic porosity considerations. If expressed on a molar basis, nitrogen solubility is significantly lower than argon solubility, in accordance with the larger size of the N2 molecule. Notably, N2 solubility in felsic melts is also much lower than CO2 solubility, even on a molar basis. This implies that the exsolution of nitrogen may drive vapor oversaturation in felsic melts derived from nitrogen-rich sediments. We also measured the partitioning of nitrogen between olivine, ... |
|---|---|
| Subject code | 660 ; 550 |
| Language | English |
| Publishing country | de |
| Document type | Article ; Online |
| Database | BASE - Bielefeld Academic Search Engine (life sciences selection) |
Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.