216 research outputs found
Developments in PF-HPLC (pneumatic-fluoropolymer high performance liquid chromatography)
Return missions are providing unique opportunities
to deepen our knowledge of the formation and
evolution of the solar system. The six Apollo missions
have been critical in shaping our understanding of the
Earth-Moon history [1], and the recent Genesis (solar
wind; e.g., [2]), Stardust (cometary dust from Wild 2;
e.g., [3,4]) and Hayabusa (dust from S-type asteroid
from Itokawa; e.g., [5]) missions brought in a wealth
of data
The REE isotopic compositions of the Earth
Lanthanides are a group of 14 naturally occurring elements with atomic numbers ranging from 57 (La) to 74 (Lu), which are also known as rare earth elements (REE). REEs are ubiquitous in minerals and rocks. The chemical properties of REEs vary as smooth functions of their atomic numbers, a
phenomenon known as the contraction of the lanthanides. This is the main control behind REE fractionation in minerals and rocks. The relative abundance of REEs is usually presented as the REE pattern by normalizing the concentrations in the sample to those in reference materials such as chondrites and shales
Tracer Applications of Noble Gas Radionuclides in the Geosciences
The noble gas radionuclides, including 81Kr (half-life = 229,000 yr), 85Kr
(11 yr), and 39Ar (269 yr), possess nearly ideal chemical and physical
properties for studies of earth and environmental processes. Recent advances in
Atom Trap Trace Analysis (ATTA), a laser-based atom counting method, have
enabled routine measurements of the radiokrypton isotopes, as well as the
demonstration of the ability to measure 39Ar in environmental samples. Here we
provide an overview of the ATTA technique, and a survey of recent progress made
in several laboratories worldwide. We review the application of noble gas
radionuclides in the geosciences and discuss how ATTA can help advance these
fields, specifically determination of groundwater residence times using 81Kr,
85Kr, and 39Ar; dating old glacial ice using 81Kr; and an 39Ar survey of the
main water masses of the oceans, to study circulation pathways and estimate
mean residence times. Other scientific questions involving deeper circulation
of fluids in the Earth's crust and mantle also are within the scope of future
applications. We conclude that the geoscience community would greatly benefit
from an ATTA facility dedicated to this field, with instrumentation for routine
measurements, as well as for research on further development of ATTA methods
Introducing Teflon-HPLC
With increasingly ambitious sample return missions and instrumentation of ever-increasing sensitivity and precision, column chromatography appears to be the neglected step-child of isotope geochemistry and little improvement has been brought to it in the past few decades. Traditional column chromatography (i.e., open-system, gravity driven) techniques
suffer from significant limitations pertaining to the overall length of column, resin size and diffusion effects, which can severely compromise separation efficiencies. Furthermore, some fine-scale separations still require complicated multi-step, highly time-consuming protocols (e.g. Ni-Mg, [1]). High-performance liquid chromatography (HPLC), while overcoming many of these limitations (e.g. a closed-system setup; the ability to pressurize the system, hence longer columns and better separation; a semi-automated set-up), is not immune to severe drawbacks. Mainly, 1) the liquid flow path often contains glass or metal parts which are easily corroded/dissolved by concentrated acids or organic solvents, leading to contamination of the samples, and 2) the electronic controls and housing are often spatially associated with the HPLC unit, drastically shortening the lifespan of the apparatus as the metallic parts rapidly corrode in these harsh chemical environments [e.g. 2]
Defining the baseline of the REE stable isotope variations in solar system materials: Earth
Mass-dependent fractionations (MDFs) of stable isotopes record critical information regarding the origin and evolution of planetary materials [1]. Studies of MDF of refractory lithophile elements (RLEs) can provide insights into condensation/evaporation and planetary accretion
processes in the early solar system. For example, the
lighter calcium isotope composition observed in
carbonaceous meteorites compared to that of the bulk
silicate Earth, enstatite and ordinary chondrites [2, 3]
may be due to the contribution of refractory dust [4, 5],
which has a light Ca isotope composition [6, 7]. In
contrast, titanium, another RLE with a similar
chemical behavior in the early solar system, was found
to have uniform isotope compositions among different
groups of meteorites including carbonaceous chondrites [8]. A potential explanation for the dichotomy of these two refractory elements could be connected to the higher 50% condensation temperature of Ti relative to Ca [9]. The isotopic results suggest that no Ti net loss took place from the CAI-forming region, while not all Ca condensed in the CAIs [7, 8]. Clearly, more proxies are needed to better understand the processes that occurred during the condensation of the solar nebula
The REE isotopic compositions of the Earth
Lanthanides are a group of 14 naturally occurring elements with atomic numbers ranging from 57 (La) to 74 (Lu), which are also known as rare earth elements (REE). REEs are ubiquitous in minerals and rocks. The chemical properties of REEs vary as smooth functions of their atomic numbers, a
phenomenon known as the contraction of the lanthanides. This is the main control behind REE fractionation in minerals and rocks. The relative abundance of REEs is usually presented as the REE pattern by normalizing the concentrations in the sample to those in reference materials such as chondrites and shales
Developments in PF-HPLC (pneumatic-fluoropolymer high performance liquid chromatography)
Return missions are providing unique opportunities
to deepen our knowledge of the formation and
evolution of the solar system. The six Apollo missions
have been critical in shaping our understanding of the
Earth-Moon history [1], and the recent Genesis (solar
wind; e.g., [2]), Stardust (cometary dust from Wild 2;
e.g., [3,4]) and Hayabusa (dust from S-type asteroid
from Itokawa; e.g., [5]) missions brought in a wealth
of data
Dopa-sensitive progressive dystonia of childhood with diurnal fluctuations of symptoms: a case report
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