Isotope selective photoionization of calcium using two-step laser excitation

The isotope specific two-step photoionization of metastable Ca atoms was investigated using a continuous wave dye laser and an Ar⁺ laser. The photoionization was performed via a transition to an autoionizing state. Therefore an ionization probability as high as 10⁻² could be obtained.     

Determination of selenium in sediment by isotope-dilution inductively coupled plasma mass spectrometry with an octapole reaction cell

A method is described for determination of selenium in sediment by isotope-dilution inductively coupled plasma mass spectrometry with an octapole reaction cell (ID–ICP–ORCMS). Sediment samples were digested with HNO₃, HClO₄, and HF, and the digestion included an elaborate evaporation process to remove bromine from the digested solution. Simple strong cation-exchange disk filtration was used to remove rare earth elements (REE) from the digested solution, because REE²⁺ seriously interfere with Se isotopes (i.e. ¹⁵⁶Gd²⁺ with ⁷⁸Se⁺, ¹⁶⁰Gd²⁺ with ⁸⁰Se⁺). Addition of acetic acid to the filtrate was examined to improve the sensitivity of ICP–ORCMS measurement of Se⁺ by means of a carbon-enhancement effect. The interfering for selenium isotopes were almost eliminated by use of H₂ as reaction gas. Interference from BrH⁺ formed in the reaction cell was negligible because the Br was removed in the evaporation process. Approximately 99.5% of REE were removed by cation-exchange disk filtration yet more than 99% of Se remained in the filtrate solution. The intensity for Se⁺ was enhanced approximately fourfold by addition of 5% (v/v) of acetic acid whereas that for was barely enhanced. Measured ⁸⁰Se/⁷⁸Se ratios in unspiked digested solutions of the sample were in good agreement with that for an Se standard solution. The analytical results for Se in the certified reference materials MESS-3 and PACS-1 were in good agreement with their certified values, with small uncertainties.      

Isotope dilution GC-MS routine method for the determination of butyltin compounds in water

A standard GC-MS instrument with electron impact ionisation has been used to develop a fast, simple and reliable method for the simultaneous determination of monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT) in water samples. Isotope dilution analysis (IDA) is used for the determination of species, taking advantage of a commercially available spike solution containing a mixture of MBT, DBT and TBT enriched in ¹¹⁹Sn. Method detection limits for 100-mL samples were between 0.18 and 0.25 ng L⁻¹ for the three butyltin compounds with typical RSD between 2 and 4% at levels between 100 and 10 ng L⁻¹, respectively. Recovery of tin species in spiked samples (natural water, wastewater and seawater) was quantitative. The stability of butyltin compounds in collected seawater samples was also studied. The addition of a 1% (v/v) glacial acetic acid preserved tin species in the samples for at least 5 days at room temperature. The IDA method was finally implemented in a routine testing laboratory and it was subsequently accredited by the Spanish National Accreditation Body according to the requirements of UNE-EN ISO/IEC 17025.     

Carbon and oxygen isotope working standards from C3 and C4 photosynthates

A preparation of organic working standards for the online measurement of ¹³C/¹²C and ¹⁸O/¹⁶O ratios in biological material is presented. The organic working standards are simple and inexpensive C₃ and C₄ carbohydrates (sugars or cellulose) from distinct geographic origin, including white sugar, toilet and XEROX papers from Switzerland, maize from Ivory Coast, cane sugar from Brazil, papyrus from Egypt, and the core of the stem of a Cyperus papyrus plant from Kenya. These photosynthetic products were compared with International Atomic Energy standards CH-3 and CH-6 and other calibration materials. The presented working standards cover a 15 ‰ range of ¹³C/¹²C ratios and 9 ‰ for ¹⁸O/¹⁶O, with a precision<±0.2 ‰ for n>10.     

Estimation of lake water—groundwater interactions in meromictic mining lakes by modelling isotope signatures of lake water

Abstract

A method is presented to assess lake water–groundwater interactions by modelling isotope signatures of lake water using meteorological parameters and field data. The modelling of δ¹⁸O and δD variations offers information about the groundwater influx into a meromictic Lusatian mining lake. Therefore, a water balance model is combined with an isotope water balance model to estimate analogies between simulated and measured isotope signatures within the lake water body. The model is operated with different evaporation rates to predict δ¹⁸O and δD values in a lake that is only controlled by weather conditions with neither groundwater inflow nor outflow. Comparisons between modelled and measured isotope values show whether the lake is fed by the groundwater or not. Furthermore, our investigations show that an adaptation of the Craig and Gordon model [H. Craig, L.I. Gordon. Deuterium and oxygen-18 variations in the ocean and the marine atmosphere. In Stable Isotopes in Oceanographic Studies and Paleotemperature, Spoleto, E. Tongiorgi (Ed.), pp. 9–130, Consiglio Nazionale delle Ricerche, Laboratorio di Geologia Nucleare, Pisa (1965).] to specific conditions in temperate regions seems necessary.     

Origins of isotopomeric polymorphism

The complex formed between 4-methylpyridine and pentachlorophenol (4MPPCP) crystallises in a triclinic space group. If the same complex is synthesized from deuterated pentachlorophenol, it crystallizes in an entirely different monoclinic polymorph. Using solid-state NMR of samples synthesized with a full range of deuteration levels, crystallized from solution or the melt, and in the presence or absence of seeds, we have confirmed that the isotopomers indeed have different thermodynamically stable crystal structures. The roots of this phenomenon of isotopomeric polymorphism apparently lie in the differences in hydrogen bonding between the polymorphs. The triclinic form has a relatively short hydrogen bond. High-field solid-state NMR shows both the ¹H chemical shift and the ²H electric quadrupole coupling of the hydrogen involved in the bond to be strongly temperature-dependent, indicating a low-lying excited state of the hydrogen bond longitudinal vibration. Inelastic neutron scattering of isotopomers of 4MPPCP has allowed us to identify the three orthogonal vibrational modes of the hydrogen in the hydrogen bond, at 29.7, 145, and 205 meV (240, 1168, and 1651 cm^?1). The longitudinal mode is the lowest in energy, and it indicates a slightly asymmetric low-barrier double-well potential. Intrinsic to such potentials is a very small difference in zero-point energies (ZPEs) between the protonated and deuterated forms. As a contrast, the monoclinic form has a comparatively normal hydrogen bond, in which the proton and deuteron ZPEs should be different by approximately 500 cm^?1. A scenario can be envisaged where the triclinic protonated form is lower in energy than the monoclinic protonated form, but the triclinic deuterated form is higher in energy than the monoclinic deuterated form. This evidently accounts for the difference in relative stabilities of the two forms upon isotope substitution.     

Sample preparation techniques for the determination of natural 15N/14N variations in amino acids by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS)

In order to identify natural nitrogen isotope variations of biologically important amino acids four derivatization reactions (t-butylmethylsilylation, esterification with subsequent trifluoroacetylation, acetylation and pivaloylation) were tested with standard mixtures of 17 proteinogenic amino acids and plant (moss) samples using GC-C-IRMS. The possible fractionation of the nitrogen isotopes, caused for instance by the formation of multiple reaction products, was investigated. For biological samples, the esterification of the amino acids with subsequent trifluoroacetylation is recommended for nitrogen isotope ratio analysis. A sample preparation technique is described for the isotope ratio mass spectrometric analysis of amino acids from the non-protein (NPN) fraction of terrestrial moss. ¹⁴N/¹⁵N ratios from moss (Scleropodium spec.) samples from different anthropogenically polluted areas were studied with respect to ecotoxicologal bioindication.     

A Spin Label Study of Membrane Alteration During Conversion of Fusarium sulphureum Macroconidia to Chlamydospores

Fusarium sulphureum is an important fungus belonging to a group of pathogenic Ascomycetes which cause root and vascular disease in cereal and vegetable crops. These organisms ordinarily grow as vegetative hyphae but under unfavorable conditions form macroconidia and chlamydospores as dispersal and survival propagules. The role of compositional and physical changes in cellular membranes during growth, survival and propagation of the pathogen provides the focus of this investigation.     

Efficient Access to Deuterated and Tritiated Nucleobase Pharmaceuticals and Oligonucleotides using Hydrogen‐Isotope Exchange

A general approach for the efficient hydrogen‐isotope exchange of nucleobase derivatives is described. Catalyzed by ruthenium nanoparticles, using mild reaction conditions, and involving either D₂ or T₂ as isotopic sources, this reaction possesses a wide substrate scope and a high solvent tolerability. This novel method facilitates the access to essential diagnostic tools in drug discovery and development: tritiated pharmaceuticals with high specific activities and deuterated oligonucleotides suitable for use as internal standards during LC‐MS quantification.     

Isotopic separation of lithium ions by capillary zone electrophoresis

Separation of ⁶Li and ⁷Li isotopes by CZE was demonstrated. The BGE contained 5 mM 4‐aminopyridine, 0.9 mM oxalic acid, 0.25 mM CTAB, and 0.25% w/v Tween 20 (рН = 9.2). The running conditions were +25 kV at 30°C with indirect photometric detection at 261 nm. Under optimal experimental conditions, the analysis time was less than 21 min. Separation of Li preparations with mole fraction of ⁶Li ranging from 3.44 up to 90.38% was demonstrated.