Observation of cerium isotope fractionation in ion-exchange chromatography of Ce(III)-malate complex

The cerium isotope fractionation between Ce(III)-malate complex in aqueous solution and cerium ions in a cation-exchange resin was conducted by displacement chromatography. The pH and the chemical composition of the eluent were optimized for maintaining the self-sharpening band boundaries and the 21 m chromatographic migration of the Ce band underwent. Graphite slurry was coated on the tantalum filament prior to sample loading for reducing the isobaric interferences in cerium isotopic ratio determination by mass spectrometry. From the experimental results, it was found that the heavier isotope was enriched in the front boundary part of the cerium adsorption band, which meant that the heavier isotope was preferentially fractionated into the Ce3+ malate complex rather than simply hydrated Ce3+ ions. The isotope separation coefficient for the 136Ce/140Ce and 142Ce/140Ce was 5.2 x 10(-5) and -1.9 x 10(-5), respectively, at 298 K.     

A systematic investigation into the mechanism of the reaction between CF3 radicals and CO/O2

A complete study of the reaction of CF(3) radicals in the presence of CO and O(2) was carried out by using isotopically labeled reagents to form, selectively, all the possible isotopomers of the intermediate trioxide, CF(3)OC(O)OOOC(O)OCF(3), and of the stable peroxide, CF(3)OC(O)OOC(O)OCF(3). Analyses were carried out by means of FTIR spectroscopy in combination with ab initio calculations. At temperatures close to 0 degrees C, the acyloxy radicals formed were shown to exist long enough to yield a statistical mixture of isotopomers. In previous reports their lifetime was considered to be too short.     

Determination of the carbon-13 content of sugars and pulp from fruit juices by isotope-ratio mass spectrometry (internal reference method). A European interlaboratory comparison

An interlaboratory comparison by ¹³C-isotope ratio mass spectrometry was organised by working group No. 1 of the European Commission of Standardisation (CEN/TC 174) in order to define the repeatability (r) and the reproducibility (R) of the ¹³C determination in sugars and pulp, isolated from the same fruit juice. Six unlabelled juices were analysed in 19 laboratories in the European Union, Australia and the USA. Three samples were authentic juices (orange, grapefruit, pineapple) and the remaining samples were the same juices with an addition of sugar at 15 g l⁻¹ (orange, pineapple) or 11.8 g l⁻¹ (grapefruit). The sugar was prepared by mixing equal amounts of beet and cane sucroses. The different laboratories used the same experimental protocol under different conditions (operator, conversion system for CO₂ preparation, mass spectrometer). The results for the sugars (r = 0.27%., R = 0.82%.) were comparable to those from an earlier ring test (r = 0.30%., R = 0.70%.), while the results for the pulp presented higher interlaboratory variability (r = 0.38%., R = 1.89%.) possibly due to experimental difficulties. Nevertheless, the RSD_R for free sugars ranged 0.9–3.2% and for pulp, 0.9–9.3%. On the basis of the Horwitz equation and taking account of the concentration of the isotopes measured, an RSD_R of 7–8% might have been expected. The experimentally determined RSD_R values were less than twice the theoretically expected values, which is a criterion of an acceptable method. The results were therefore considered to be acceptable by specialists in the field of isotopic analysis, and the method applied was found to improve the sensitivity of the ¹³C determination for the detection of sugar addition in fruit juices.     

ICP-MS measurements of lead isotopic ratios in soils heavily contaminated by lead smelting: tracing the sources of pollution

The Pb isotopic composition (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁶Pb) in smelter-impacted soils was measured using a quadrupole-based ICP-MS. Four forest/tilled soil profiles were sampled according to the distance from the lead smelter in Píbram (Czech Republic), prevailing wind direction, geological background and soil type. The results were compared with the Pb isotopic composition of bedrocks and waste materials from Pb metallurgy (smelting slags, air-pollution-control residues). The isotopic composition of soils confirms the predominant role of metallurgy on the general pollution in the area. The highly contaminated soils from the vicinity of the smelter contain up to 35,300 mg Pb kg^–1 and exhibit an isotopic composition close to that of car battery processing (²⁰⁶Pb/²⁰⁷Pb up to 1.177). A coupled concentration/isotopic study of soil profiles showed that the smelter-induced pollution had penetrated even to the mineral soil horizons, indicating an important vertical mobility of Pb contaminant within the soil profile. The calculated downward penetration rate of Pb in soils ranges from 0.3 to 0.36 cm year^–1.     

Rapid and precise determination of Sr and Nd isotopic ratios in geological samples from the same filament loading by thermal ionization mass spectrometry employing a single-step separation scheme

Thermal ionization mass spectrometry (TIMS) offers the excellent precision and accuracy of the Sr and Nd isotopic ratio analysis for geological samples, but this method is labour intensive, expensive and time-consuming. In this study, a new analytical protocol by TIMS is presented that aims at improving analytical efficiency and cutting down experimental cost. Using the single-step cation exchange resin technique, mixed Sr and rare earth elements (REEs) fractions were separated from matrix and evaporated to dryness. Afterwards, mixed Sr + REEs fractions were dissolved and loaded onto the same Re filament using 1 μL of 2 M HCl. Then, Sr and Nd were sequentially measured without venting using TIMS. In contrast to conventional TIMS methods, the merits of this analytical protocol are its cost- and time-saving adaptations. The applicability of our method is evaluated by replicated measurements of ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd for nine international silicate rock reference materials, spanning a wide range of bulk compositions. The typical internal precision in this study is ca. 0.001% (RSE) for ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd; the analytical results obtained for these standard rocks show a good agreement with reported values, indicating the effectiveness of the proposed method.     

Isotopic Determination of Silicon by Mass Spectrometry in Plants and Soils Labeled with 30Si

Abstract

A method for isotopic determination of silicon by mass spectrometry in plants and soils labeled with ³⁰Si is reported. The development of this method is for use with studies involving the physiological process of absorption, transport, and redistribution of Si in the soil-plant system by use of the stable isotope ³⁰Si as a tracer. The procedure leads to SiF₄ formation, and the isotopic determination of Si was based on the measurements of the ²⁸SiF₃ ⁺, ²⁹SiF₃ ⁺, and ³⁰SiF₃ ⁺ signals. Relative standard deviation of ³⁰Si abundance measurements (n = 6) were lower than 0.1%, and the detection limit was 0.5 mg Si (dry mass).     

A Branched Diterpene Cascade: The Mechanism of Spinodiene Synthase from Saccharopolyspora spinosa

A diterpene synthase from Saccharopolyspora spinosa was found to convert geranylgeranyl diphosphate into the new natural products spinodiene A and B, accompanied by 2,7,18‐dolabellatriene. The structures and the formation mechanism of the enzyme products were investigated by extensive isotopic labelling experiments, which revealed an unusual branched isomerisation mechanism towards the neutral intermediate 2,7,18‐dolabellatriene. A Diels–Alder reaction was used to convert the main diterpene product with its rare conjugated diene moiety into formal sesterterpene alcohols.     

钨元素的发现及其概念的发展

1781年,瑞典化学家舍勒在白钨矿中发现了钨酸,预测其中一定含有一种新金属元素,并将其命名为钨(Tungsten)。1783年,西班牙化学家德鲁亚尔兄弟从黑钨矿中成功提取出了舍勒所说的新金属单质,将其命名为钨(Wolfram)。1803年,英国化学家道尔顿原子论的提出,赋予钨元素新的含义:具有一定质量的钨原子。1930年以后,钨同位素的发现使人们对钨元素有了新认识,并逐渐形成了现代钨元素的概念。关于钨元素的认识经历了从假说到客观存在、从定性到定量、从宏观到微观的发展历程。钨元素概念的演变体现了科学思想和科学方法的进步。     

Characterizing the origins of bottled water on the South Korean market using chemical and isotopic compositions

We analyzed the major elements and stable isotopes of oxygen, hydrogen, and carbon (dissolved inorganic carbon: DIC) in various types of bottled water (domestic and foreign) commercially available in South Korea to classify the water types and to identify their origins. Only marine waters and some sparkling waters could be discriminated by their physicochemical compositions. Oxygen and hydrogen isotopes made marine waters more distinguishable from other water types. The determination of the carbon isotope composition of DIC was clearly useful for distinguishing between naturally and artificially sparkling waters. In addition, statistical analysis also appeared to aid in the discrimination of bottled water types. Our results indicate that a method that combines chemical and stable isotope composition analysis with statistical analysis is the most useful for discriminating water types and characterizing the origins of bottled water.     

Determination of biogenic amines in food samples using derivatization followed by liquid chromatography/mass spectrometry

A liquid chromatography (LC)/mass spectrometry method was developed for the determination of selected biogenic amines in various fish and other food samples. It is based on a precolumn derivatization of the amines with succinimidylferrocenyl propionate under formation of the respective amides and their reversed-phase liquid-chromatographic separation with subsequent electrospray ionization mass-spectrometric detection. Deuterated putescine, cadaverine, and histamine are added prior to the derivatization as internal standards that are coeluted, thus allowing excellent reproducibility of the analysis to be achieved. Depending on the analyte, the limits of detection were between 1.2 and 19.0 mg/kg, covering between 2 and 3 decades of linearity. The limit of detection and the linear range for histamine are suitable for the surveillance of the only defined European threshold for biogenic amines in fish samples. Compared with the established ortho-phthalaldehyde (OPA)/LC/fluorescence method, the newly developed method allows an unambiguous identification of the biogenic amines by their mass spectra in addition to only retention times, a fivefold acceleration of the separation, and independency from the sample matrix owing to the isotope-labeled internal standards. Various fish, calamari, and salami samples were successfully analyzed with the new method and validated with an independent OPA/LC/fluorescence method.