Synthesis of a chitosan-based chelating resin and its application to the selective concentration and ultratrace determination of silver in environmental water samples

A novel chelating resin using chitosan as a base material, ethylenediamine-type chitosan, has been synthesized for the first time in the present study, and applied to the collection/concentration of ultratrace amounts of silver in environmental water samples. In the present study, ultratrace amounts of silver collected on the resin were eluted and determined by ICP-MS. The resin packed in a 1 mL mini column could adsorb silver selectively and quantitatively at a flow rate of 2 mL min(-1) in the wide pH range from 1 to 8, and silver adsorbed on the resin could be easily recovered by passing 1 M nitric acid as an eluent into the column. High adsorption capacity for silver at pH 5, 0.37 mmol mL(-1) of the resin, was achieved, and t(1/2) of the adsorption is less than 5 min. The effect of chloride on the collection of silver was examined by varying chloride concentrations from 10(-4) to 0.75 M; the results showed that the present resin can be used for the collection/concentration of ultratrace amounts of silver in natural waters, as well as seawater. To ensure the accuracy and the precision of the method, CASS-4 near shore seawater reference material from the NRCC has been analyzed. This is not a certified SRM for silver, but has been used for comparative silver analysis by several groups, who report very similar results to those that are reported here. The developed method using ethylenediamine-type chitosan resin gives 0.7 pg mL(-1) of the detection limit when 50-fold enrichment was used. The proposed method was successfully applied to the determination of silver in tap, river, and seawater samples

The Great American Biotic Interchange: Dispersals, Tectonics, Climate, Sea Level and Holding Pens

The biotic and geologic dynamics of the Great American Biotic Interchange are reviewed and revised. Information on the Marine Isotope Stage chronology, sea level changes as well as Pliocene and Pleistocene vegetation changes in Central and northern South America add to a discussion of the role of climate in facilitating trans-isthmian exchanges. Trans-isthmian land mammal exchanges during the Pleistocene glacial intervals appear to have been promoted by the development of diverse non-tropical ecologies

Skin Stem Cell Hypotheses and Long Term Clone Survival - Explored Using Agent-based Modelling

Epithelial renewal in skin is achieved by the constant turnover and differentiation of keratinocytes. Three popular hypotheses have been proposed to explain basal keratinocyte regeneration and epidermal homeostasis: 1) asymmetric division (stem-transit amplifying cell); 2) populational asymmetry (progenitor cell with stochastic fate); and 3) populational asymmetry with stem cells. In this study, we investigated lineage dynamics using these hypotheses with a 3D agent-based model of the epidermis. The model simulated the growth and maintenance of the epidermis over three years. The offspring of each proliferative cell was traced. While all lineages were preserved in asymmetric division, the vast majority were lost when assuming populational asymmetry. The third hypothesis provided the most reliable mechanism for self-renewal by preserving genetic heterogeneity in quiescent stem cells, and also inherent mechanisms for skin ageing and the accumulation of genetic mutation

Magnetic properties of hemocyanin

The primary purpose of this investigation was to determine the magnetic properties of hemocyanin in order to elucidate the oxygenation reaction. However, a number of other properties were examined as a preliminary basis for this work. These experiments were also of value in demonstrating the similarity of the hemocyanin used to the other hemocyanins and hence of the applicability of the magnetic work to these other proteins. As the hemocyanins are a class of proteins well adapted to studies from a comparative point of view, these results are of interest in themselves as the animal used was of a group not yet investigated. In order to increase the facility with which these comparative deductions are made I have devoted some space to results on other hemocyanins. As no review of the hemocyanins has appeared for eight years, and much important work has been done meanwhile, I have felt justified in including some of the results of the recent work that bear on the final interpretation of the magnetic experiments. The animal chosen for use was the giant key-hole limpet, Megathura crenulata, a Streptoneuran of the class Gasteropoda, found on the rocks in several places along the Pacific coast. For the convenience of those who are not acquainted with all of the species mentioned I have included a table of common names at the end of the paper