Accurate and Efficient SIMS Oxygen Isotope Analysis of Composition-Variable Minerals: Online Matrix Effect Calibration for Dolomite.

High-quality oxygen isotope analysis of composition-variable minerals (e.g., ubiquitous carbonates) using secondary ion mass spectrometry (SIMS) is extremely challenging. The classical off-line procedure, which requires additional electron probe microanalyzer (EPMA) chemical compositions for calibrating instrumental mass fractionation (IMF), is inherently inaccurate and analytically inefficient. In this study, the first accurate and paired SIMS analysis of δ18O and Fe# [molar Fe/(Mg + Fe)] in dolomite is reported. Based on five newly developed dolomite O-isotopic standards with an Fe# range of 0.01-0.35 obtained by SIMS, a novel accurate and rapid online matrix effect calibration method for dolomite O-isotope analysis was developed using concurrent SIMS 18O-16O-56Fe16O-24Mg16O measurements without additional chemical electron probe microanalysis. A logistic equation was proposed as the best-fit curve to represent the δ18O matrix effect based on the 56Fe16O/24Mg16O ratios. For CTD-4 carbonatitic dolomite with variable Fe# but homogeneous oxygen isotopes, the off-line method exhibited highly variable apparent δ18O values in the range of 5.74-10.11‰. The online method yielded a homogeneous δ18O value of 7.94 ± 0.34‰ (2SD, n = 40), which is comparable with that of bulk analysis (7.94 ± 0.20‰; 2SD). Comprehensive analyses validated the online method as the best strategy for performing accurate δ18O analysis of samples with highly heterogeneous compositions. Based on its accuracy, simplicity, and economic feasibility, this method has potential applications in the analysis of composition-complex dolomites, detrital dolomites, and other precious terrestrial and extraterrestrial materials.

Direct High-Precision Measurements of the (87)Sr/(86)Sr Isotope Ratio in Natural Water without Chemical Separation Using Thermal Ionization Mass Spectrometry Equipped with 10(12) Ω Resistors.

Thermal ionization mass spectrometry (TIMS) allows excellent precision for determining Sr isotope ratios in natural water samples. Traditionally, a chemical separation procedure using cation exchange resin has been employed to obtain a high purity Sr fraction from natural water, which makes sample preparation time-consuming. In this study, we present a rapid and precise method for the direct determination of the Sr isotope ratio of natural water using TIMS equipped with amplifiers with two 10(12) Ω resistors. To eliminate the (87)Rb isobaric interference, Re ribbons are used as filaments, providing a significant advantage over W ribbons in the inhibition of Rb(+) emission, based on systematically examining a series of NIST SRM987 standard doping with various amounts of Rb using Re and W ribbons. To validate the applicability of our method, twenty-two natural water samples, including different water types (rain, snow, river, lake and drinking water), that show a large range in Sr content variations (2.54-922.8 ppb), were collected and analyzed from North and South China. Analytical results show good precision (0.003-0.005%, 2 RSE) and the method was further validated by comparative analysis of the same water with and without chemical separation. The method is simple and rapid, eliminates sample preparation time, and prevents potential contamination during complicated sample-preparation procedures. Therefore, a high sample throughput inherent to the TIMS can be fully utilized.

An apparatus for plasma cleaning and storage of transmission electron microscopy specimens and specimen holders.

The transmission electron microscopy (TEM) specimen with thickness in nanometer scale is susceptible to hydrocarbon contamination and oxidation, and the specimen holder is also susceptible to contaminants, which would deteriorate the quality of TEM imaging and degrade the efficiency of TEM experiments. Conventional pretreatment devices often have limited functions and low practicability, which may cause problems for TEM specimens and holders. In this work, a multifunctional apparatus for plasma cleaning and storage of TEM specimens and specimen holders is developed based on the specific design of the vacuum joints. The apparatus includes a plasma cleaning system, holder storage station, and specimen storage station, which share the same vacuum system. The cleaning of hydrocarbon contaminants on the specimen and storage of the specimens and holders can be achieved simultaneously in this apparatus. TEM imaging and energy-dispersive X-ray spectroscopy (EDS) analyses of two treated specimens using the apparatus demonstrated that it could effectively remove hydrocarbon contaminants on the specimen. The holder storage station, used to preserve TEM holders in vacuum conditions, can also be modified as a specimen storage station by an appropriate design of the specimen storage platform, in which specimens are protected from water and contaminations. The designed apparatus not only robustly avoids damage to the ultrathin specimen and holders but also improves the working efficiency and reduces costs. These advantages could make our apparatus more appealing for the complement to the present commercial plasma cleaning and storage devices. HIGHLIGHTS: An apparatus for the pretreatment of transmission electron microscopy (TEM) specimens and specimen holders with three functions-plasma cleaning, holder storage, and specimen storage-was designed and fabricated. Using this single apparatus, the cleaning of hydrocarbon contaminants on the specimen and storage of the specimens and holders can be achieved simultaneously. The designed apparatus can not only robustly avoid damage to the ultrathin specimen and holders but also improve the working efficiency and reduce costs by adopting a single vacuum system. These advantages could make our apparatus more appealing for the complement to the present commercial plasma cleaning and storage devices.

Simultaneous determination of 143Nd/144Nd and 147Sm/144Nd ratios and Sm-Nd contents from the same filament loaded with purified Sm-Nd aliquot from geological samples by isotope dilution thermal ionization mass spectrometry.

Isotope dilution thermal ionization mass spectrometry (ID-TIMS) is the standard technique used to achieve precise (143)Nd/(144)Nd and (147)Sm/(144)Nd isotope ratios and accurate elemental concentrations of Sm-Nd. However, in previous studies, purified Sm and Nd fractions must be individually loaded onto different filaments for their accurate determination using TIMS because of severe isobaric interferences. Thus, the classical ID-TIMS technique is time consuming and laborious. In this study, a new method is proposed, which is able to acquire both ratios of (143)Nd/(144)Nd and (147)Sm/(144)Nd and concentrations of Sm-Nd simultaneously on the same filament arrangement. The measurement time and filament consumption are reduced by 50% with the current method, and therefore, the operation cost of TIMS is significantly reduced. A mixed (152)Sm-(148)Nd spike was employed to achieve accurate results after spike subtraction and isobaric interference corrections. Results obtained from a series of standard rock samples are in good agreement with recommended values, within ±0.003% for the (143)Nd/(144)Nd ratio and ±1% for the (147)Sm/(144)Nd ratio.

Body Composition Analysis by Using Bioelectrical Impedance in a Young Healthy Chinese Population: Methodological Considerations.

OBJECTIVE: To develop a new bioelectrical impedance analysis (BIA) model for analyzing body composition by using isotope dilution, magnetic resonance imaging (MRI), and dual-energy X-ray absorptiometry (DEXA) as the reference methods in young healthy Chinese populations. METHODS: Thirty healthy participants were enrolled. Their body composition was analyzed using BIA and 3 reference methods. We established a model that uniformed data from 3 references methods (isotope, MRI, and DEXA) into 1 formula. This model was further validated with 209 participants. RESULTS: The following BIA body composition adjustment model was developed: [Formula: see text], where X represents the impedance index; when K = 1, 2, and 3, Y represents total body water, fat mass, and bone mass, respectively. The prediction accuracy of this formula was 93.3%. By incorporating the data matrix, the protein mass was calculated using BIA: [Formula: see text]. In the verification part of this study, the lean body mass measured using DEXA and BIA was 43.02 ± 8.34 kg and 45.85 ± 8.81 kg, respectively. Analysis indicated that the model fit was extremely favorable ( R2 = .9997, P < .001). CONCLUSIONS: The accuracy of BIA measurement on body composition and protein mass is significantly improved by our work.