Problems in obtaining precise and accurate Sr isotope analysis from geological materials using laser ablation MC-ICPMS

This paper reviews the problems encountered in eleven studies of Sr isotope analysis using laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) in the period 1995–2006. This technique has been shown to have great potential, but the accuracy and precision are limited by: (1) large instrumental mass discrimination, (2) laser-induced isotopic and elemental fractionations and (3) molecular interferences. The most important isobaric interferences are Kr and Rb, whereas Ca dimer/argides and doubly charged rare earth elements (REE) are limited to sample materials which contain substantial amounts of these elements. With modern laser (193 nm) and MC-ICPMS equipment, minerals with >500 ppm Sr content can be analysed with a precision of better than 100 ppm and a spatial resolution (spot size) of approximately 100 μm. The LA MC-ICPMS analysis of 87Sr/86Sr of both carbonate material and plagioclase is successful in all reported studies, although the higher 84Sr/86Sr ratios do suggest in some cases an influence of Ca dimer and/or argides. High Rb/Sr (>0.01) materials have been successfully analysed by carefully measuring the 85Rb/87Rb in standard material and by applying the standard-sample bracketing method for accurate Rb corrections. However, published LA-MC-ICPMS data on clinopyroxene, apatite and sphene records differences when compared with 87Sr/86Sr measured by thermal ionisation mass spectrometry (TIMS) and solution MC-ICPMS. This suggests that further studies are required to ensure that the most optimal correction methods are applied for all isobaric interferences

Confirmatory factor analysis of the greek version of the competitive state anxiety inventory-2

The evaluation of the uptake of nanomaterials by cells in vitro tests is of great relevance to understand potential toxicity mechanisms of nanomaterials. As an example, the uptake of medium-sized nanosilver (size range of 50 and 75. nm) was studied closely for a relevant human lung cell line (THP-1). Time dependent uptake was studied in relation to different cell culture media with or without the addition of fetal calf serum (FCS). After cell isolation, washing, acid digestion and quantification of silver (Ag) by inductively coupled plasma mass spectrometry (ICPMS) were applied to study the general uptake. It is demonstrated that the uptake of Ag (from 75. nm Ag nanoparticles) is a factor of 5 higher in a medium without FCS in comparison to the medium with FCS. In addition, the stability and the abundance of Ag nanoparticles in the supernatant after cell exposure were studied in relation to different timings. By means of asymmetric flow field flow fractionation (AF4) for the size dependent particle separation and an on-line hyphenation to the sensitive elemental detection by ICPMS, different Ag particles were separated and further identified. By combining results from the total uptake of Ag by cells with results obtained from the analysis of the supernatant, total recoveries of 98 to 104% were determined in relation to the exposed concentration of Ag.Finally, the influence of the medium composition (with or without FCS) on the stability of 50. nm Ag nanoparticles was studied directly after spiking. A method by AF4-ICPMS was applied and the obtained fractograms confirm a clear influence of the different composed media composition and particle size on cellular uptake.The developed and applied ICPMS methods were found to be suitable approaches to evaluate the potential uptake of inorganic nanoparticles by cells

Strontium and lead isotope ratios in human hair: investigating a potential tool for determining recent human geographical

Three cleaning techniques that remove external contamination of human hair are assessed to investigate the potential use of Sr and Pb isotope composition of hair for human provenancing. These techniques are; (i) a centrifugation technique using diiodomethane where hair and soil particles are separated by density difference; (ii) a leaching technique of the hair surface using 2 M HN

Physiological responses of three species of marine pico-phytoplankton to ammonium, phosphate, iron and light limitation

Experiments were conducted with three species of marine pico-phytoplankton: Synechococcus sp. (CCMP 839), Pelagomonas calceolata (CCMP 1756) and Prasinomonas capsulatus (CCMP 1617) in order to collect physiological parameters for pico-phytoplankton to be utilised in Ocean Biogeochemical Climate Models. The main parameters to follow the effects of ammonium, phosphate, iron and light limitation were cell growth rates (µ), half saturation constants for growth (Km), N, P and Fe quota (per cell or per mol C), and photochemical quantum efficiency (Fv/Fm). The nitrate and phosphate limitation experiments demonstrated that the small phytoplankton species could grow at low N and P concentrations. Km values were in the micro-molar (NH4+) and sub-micro-molar (PO43-) range. N and P quota were in the femto-molar range per cell and varied from nutrient-deplete to nutrient-replete conditions. Fv/Fm values were only adversely affected at the lowest N and P concentrations in these experiments. In the Fe limitation experiments, it was shown that all three species were adversely affected only at extremely low Fe concentrations. Iron chelating agents had to be added to force the species in Fe limitation till ultimately growth stopped. Km values with respect to dissolved Fe were in the femto-molar range. Fe quota were in the low zepto-molar (10-21 M) range per cell, and varied considerably from Fe limiting to Fe replete growth conditions. Fv/Fm values diminished only at the lowest iron concentrations. In the light limitation experiments, growth rates and photochemical quantum efficiencies were adversely affected only at irradiance levels below 10 µmol photons m-2 s-1. These results indicate that the pico-phytoplankton species will hardly ever be completely stopped in their growth by NH4+, PO43-, Fe or light (separately) under natural conditions.

Picophytoplankton - a comparative study of their biochemical composition and photosynthetic properties

Picophytoplankton are a small or major component of the phytoplankton community and present in all oceanic systems, from pole to pole. They dominate in the low chlorophyll biomass areas, such as the (sub)tropical regions, but also contribute considerably (up to 20%) in the high chlorophyll biomass areas. The ecosystems of occurrence contrast significantly in physical and chemical settings. This includes a strongly mixed upper water column replete in nutrients as well as a strongly thermally stratified euphotic zone depleted in nutrients at the surface with a steep inverse light and nutrient gradient. These changes impose a strong impact on the composition of the picophytoplankton community but also on the biochemical and physiological properties of the species present. In particular, the pigmentation and cellular carbon, nitrogen and phosphorus quota and requirement will differ from a stratified compared to a well-mixed water column. As a result no characteristic values for the parameters required for this specific algal group in a global phytoplankton carbon model (the SWAMCO model,Lancelot et al. (2000), Deep-Sea Res. I, 47, 1621) can be given. In the present paper an inventory is made of the biochemical, physiological and photosynthetic parameters of two species of cyanobacteria (Prochlorococcus and Synechococcus) and the pico-size class fraction of the eukaryote phytoplankton component. Other groups of phytoplankton, such as diatoms, Trichodesmium, Phaeocystis and coccolithophorids, will be discussed in separate papers in this issue. This inventory is a mixture of laboratory experiments using well-defined algal populations as well as data derived from field surveys including a mixture of species. Where possible, the relevance of the parameters will be discussed in relation to the nature of the physico-chemical conditions of the area of occurrence