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In this research work, we investigated the possibility of using mixtures of monoisotopic elements (93Nb/89Y, 165Ho/159Tb and 209Bi/197Au) as calibrators for accurate determination of isotope ratios by multicollector mass spectrometry (MC-ICP-MS). The potential advantage of using monoisotopic elements for calibration lies in their significantly lower uncertainty in atomic masses. This would certainly affect the uncertainty of a measured isotope ratio after data processing, particularly if absolute isotope ratios are being evaluated. Model isotopic systems (87Sr/86Sr–93Nb/89Y, 92Zr/90Zr–93Nb/89Y, 208Pb/207Pb–209Bi/197Au and 167Er/166Er–165Ho/159Tb) were selected and the Internal Standard method (Russell's law) and optimized regression model (ORM) for isotope measurements, using the mentioned mixtures of monoisotopic elements as calibrators, were applied. The precision and trueness of the obtained results were assessed. For example, the 167Er/166Er isotope ratio in a certified reference material of erbium was measured using a gravimetric mixture of Ho and Tb as well as a 160Gd/158Gd pair (NRC GADS-1) as instrumental isotopic fractionation (IIF) calibrators in ORM. Although the average result for both approaches was in the range of instrumental error (0.68223 ± 0.00351 with 165Ho/159Tb and 0.68236 ± 0.00034 with 160Gd/158Gd), the precision was ten times lower when a mixture of monoisotopic elements was used for correction. Based on the results obtained, it was assessed that Russell's law does not provide a correct description for systems with a mixture of two monoisotopic elements, probably due to the assumption of equal IIF for the analyte and internal calibrator. In our opinion, such an assumption is not true in a system when the internal calibrator is a pair of two different elements. A new mathematical description of such a system could enable the introduction of a suitable correction. The ORM method is free from assumptions about the same IIF for individual chemical entities and for this reason it looks more encouraging and shows the potential to be useable even with a mixture of monoisotopic elements as calibrators. In this paper we present experimental results confirming this assumption, although the current challenge is to ensure a sufficiently high precision of calibrator ratio measurement and, consequently, better regression linearity and higher precision of the obtained results. [ABSTRACT FROM AUTHOR]

This study evaluates the feasibility of using the internal standard (IS) method and optimized regression model (ORM) to determine lead isotope ratios without separating Pb from many different types of matrices. The effect of typical interferents at increasing concentrations was investigated using model samples. We have demonstrated that Pb isotope ratio measurements without matrix separation give equally accurate and precise results as those obtained with matrix separation. Finally we used a new protocol to measure the isotope ratio of Pb in environmental, geological and archaeological samples with very limited availability (3 mg) and low lead content (30 mg kg−1). Such samples have so far been problematic for MC-ICP-MS isotopic analysis due to the difficulties with separating such small amounts of lead using ion exchange resins. Lead isotope ratios were measured without separation of lead from the sample using two protocols. In the first, the internal standard method was used as a means of calibration. In the second, the optimized regression model was used. In this case there were no statistically significant differences between the protocols compared. Both approaches gave statistically similar results. The protocol using IS is recommended as it is significantly simpler and less laborious and consumes lower volumes of sample solution. The protocol we developed can be applied to a wide range of samples (following some recommendations). To demonstrate the usefulness of the new procedure, we applied it to different types of samples containing lead at different concentrations. In particular, we focused on historical samples because their availability is very limited and collecting a sufficiently large sample is always a major problem. Where possible, we compared our results with literature values. The new protocol, by eliminating the sample preparation step, allowed us to measure about four times more samples per day (about 12–15) compared to the classical method (with Pb separation using ion exchange resins). We also present, for the first time, a new method for the non-destructive sampling of manuscripts for isotopic analysis, involving the extraction of lead from the object into indicator papers soaked in 4,7-diphenyl-1,10-phenanthroline. [ABSTRACT FROM AUTHOR]

Isotope fractionation of metals/metalloids in biological systems is an emerging research area that demands the application of state-of-the-art analytical chemistry tools and provides data of relevance to life sciences. In this work, Se uptake and Se isotope fractionation were measured during the biofortification of baker's yeast (Saccharomyces cerevisiae)—a product widely used in dietary Se supplementation and in cancer prevention. On the other hand, metabolic labeling with 15N is a valuable tool in mass spectrometry-based comparative proteomics. For Se-yeast, such labeling would facilitate the assessment of Se impact on yeast proteome; however, the question arises whether the presence of 15N in the microorganisms affects Se uptake and its isotope fractionation. To address the above-mentioned aspects, extracellularly reduced and cell-incorporated Se fractions were analyzed by hydride generation–multi-collector inductively coupled plasma–mass spectrometry (HG MC ICP–MS). It was found that extracellularly reduced Se was enriched in light isotopes; for cell-incorporated Se, the change was even more pronounced, which provides new evidence of mass fractionation during biological selenite reduction. In the presence of 15N, a weaker preference for light isotopes was observed in both, extracellular and cell-incorporated Se. Furthermore, a significant increase in Se uptake for 15N compared to 14N biomass was found, with good agreement between hydride generation microwave plasma–atomic emission spectrometry (HG MP–AES) and quadrupole ICP–MS results. Biological effects observed for heavy nitrogen suggest 15N-driven alteration at the proteome level, which facilitated Se access to cells with decreased preference for light isotopes. [ABSTRACT FROM AUTHOR]

One of the first movements of early modern humans out of Africa occurred 130-100 thousand years ago (ka), when they migrated northward to the Levant region. The climatic conditions that accompanied this migration are still under debate. Using high-precision multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS) U-Th methods, we dated carbonate cave deposits (speleothems) from the central and southern Negev Desert of Israel, located at the northeastern margin of the Saharan-Arabian Desert. Speleothems grow only when rainwater enters the unsaturated zone, and this study reveals that a major cluster of wet episodes (the last recorded in the area) occurred between 140 and 110 ka. This episodic wet period coincided with increased monsoonal precipitation in the southern parts of the Saharan-Arabian Desert. The disappearance at this time of the desert barrier between central Africa and the Levant, and particularly in the Sinai-Negev land bridge between Africa and Asia, would have created a climatic 'window' for early modern human dispersion to the Levant. Keywords: Negev Desert, speleothems, U-Th dating, paleoclimate, out of Africa.

Measurements of [sup.44]Ca/[sup.42]Ca and [sup.143]Nd/[sup.144]Nd isotope ratios in carbonate fluorapatite (CFA) through the Aptian-Eocene section of the Negev (Israel), together with quantified rates of P and Ca accumulation and bulk sedimentation, permit an examination of the relationships of these five factors to Tethyan phosphogenesis. The data provide an Aptian-Eocene (ca. 70 Ma) record of the Ca isotope composition of 35 CFA samples (24 of which were also analyzed for Nd isotopes), representing 11 time-stratigraphic phosphate horizons within the sequence. The [[delta].sup.44]Ca values are significantly lower in the Aptian-Albian samples ([[delta].sup.44]Ca = -0.11 [per thousand] to -0.06 [per thousand]) than in the Campanian-Eocene samples ([[delta].sup.44]Ca = +0.22 [per thousand] to +0.42 [per thousand]), whereas the eNd(r) values increase from continental crust like in the Aptian-Albian [[epsilon].sub.Nd(T)] = -10.9] to more radiogenic, Pacific-like [eNd(r) = -6.6 to -6.1] in the Campanian. Both peaks of [[delta].sup.44]Ca and eNd(r) in the Campanian coincide with the peak of Tethyan phosphogenesis in the Negev, which is marked by a sharp increase of P accumulation rates (from Keywords: [[delta].sup.44]Ca, [[epsilon].sub.Nd(T)], phosphogenesis, Aptian-Eocene, Tethys, Negev.

The chronology of the Sea of Galilee is compared to levels of lead in soil samples from different depths of the sea bed. Lead samples show a gradual rise in lead levels since 1920, with abrupt changes during different events such as the drying out of the Hula Swamp. Lead concentration statistics are prepared chronologically in charts and graphs.

The work demonstrates a novel analytical method for compound-specific carbon isotope analysis in organic compounds by gas chromatography hyphenated with MC-ICPMS. Precision down to 0.3‰ (1σ) was attained for analytes containing as low as 0.6 nmol of carbon. Tuning of MC-ICPMS was performed on the background signals for m/z 12 and m/z 13. MC-ICPMS was operated in a low-resolution mode (m/Δm ∼ 300) and the instrumental parameters were optimized for the minimum m/z 13 to m/z 12 ratio. Good agreement between the δ13C values measured for ethylene dibromide, 2-chloroethyl benzene and naphthalene by GC/MC-ICPMS and the values determined for these compounds by GC-C-IRMS was observed. Determination of the carbon isotope ratio in the VPDB scale, as well as the absolute 13C/12C values was performed by applying an internal standard with known carbon isotope ratio. [ABSTRACT FROM AUTHOR]