Distribution of <Superscript>137</Superscript>Cs, <Superscript>40</Superscript>K, <Superscript>232</Superscript>Th and <Superscript>238</Superscript>U in coastal marine sediments of Margarita Island,Venezuela

This work presents the results of ¹³⁷Cs, ⁴⁰K, ²³²Th and ²³⁸U concentration (Bq kg⁻¹) values in coastal marine sediments collected from 38 sites along the coastline of the island of Margarita, Venezuela. The purpose was to determine baseline values for these radionuclides in surface marine sediments and to detect if there were any anomalously high concentration values. Only three of the 38 sediments analyzed had measurable values above the detection limit of 0.9 Bq kg⁻¹ for ¹³⁷Cs and the highest only being 1.4 Bq kg⁻¹. While, the concentration (Bq kg⁻¹) ranges for the primordial radionuclides, ⁴⁰K, ²³²Th and ²³⁸U were as follows: 12.2–211.7, <1.5–9.8 and <4.4–20.7, respectively. These concentration ranges for the primordial radionuclides can be considered as baseline values for surface marine sediments for areas that are considered not polluted by man or contaminated by nature. Finally, the concentration range of ¹³⁷Cs can also be employed as baseline values, which only seem to have been the result of the atmospheric testing of nuclear weapons in the past.     

Speciation of nickel by HPLC-UV/MS in pea nodules

A new and sensitive methodology based on normal phase HPLC has been developed for the speciation of nickel in low-complexity plant extracts. The method combines a silica stationary phase column, a 9:1 (v/v) hexane:ethanol mixture as mobile phase, and the detection of nickel complexes by either UV or MS. The developed methodology was applied to the speciation of nickel complexes in the cytoplasm of pea root nodules. Results obtained indicate that nickel citrate and nickel malate accounts for 99% of nickel present in pea nodule cytoplasm fraction. The low detection limit of the method (<0.2 nM) enables nickel speciation in non-hyperaccumulator plants.     

Homochirality and chemical evolution: new vistas and reflections on recent models

This report revises and scrutinizes recent arguments, theories, and hypotheses related to the emergence of homochirality. Since the whole treatment would involve multiple and varied scenarios, emphasis is put only on some processes, believed (or claimed) to be prebiotically credible. A particular purpose is to introduce less-travelled paths in which enantioenrichment does not emerge from amplification mechanisms. Some food for thought is provided in an attempt to reduce the gap between existing abiotic hypotheses and the more elusive and conjecturable biotic proposals. A series of novel models have been suggested to reconcile and incorporate chirogenesis into chemical evolution fueled by prebiotic building blocks. All in all, we want to offer new vistas into a never-ending pursuit in the hope that the present considerations will elicit further stimulus, analysis, and experiments in various domains.     

Investigation of the stability of selenoproteins during storage of human serum by size-exclusion LC-ICP-MS

The stability of selenium-containing proteins in human serum was investigated by size-exclusion chromatography-ICP-MS under non-denaturating conditions. The peak characteristic to glutathione peroxidase (GSHPx) (tetramer) was the most affected; peaks of the GSHPx monomer and of selenite were found to appear with time. No trace of selenite was present in fresh samples, which suggest that the presence of this species in serum may be an artifact of storage. The mass balance of selenium species indicates that some of selenium is lost as a function of the storage time.     

Indirect determination of oxygen dissolved in water by atomic absorption spectrometry

Summary Indirect Determination of Oxygen Dissolved in Water by Atomic Absorption Spectrometry O₂ dissolved in aqueous medium reacts quantitatively with thallium metal according to O₂+4 Tl+2 H₂O 4 Tl⁺+4 OH^–. The reaction takes place in a glass column filled up with small pieces of sheet metal. The Tl⁺ formed is measured by atomic absorption spectrometry. We study the influence of several factors (pH, temperature, salinity of the water). The results obtained from a statistical sample were compared with those provided by the amperometric method for direct determination of dissolved O₂ and we found a high degree of consistency between them.     

A SEM–EDX study of highly stable supported liquid membranes based on ionic liquids

This work evaluates the operational stability of six different supported liquid membranes (SLMs) based on ionic liquids (ILs). [bmim⁺][PF₆⁻]_, [bmim⁺][BF₄⁻] and [bmim⁺][NTf₂⁻] were used as supporting phase in Nylon^® and Mitex^® membranes. Scanning electron microscopy (SEM) combined with energy dispersive X-ray (EDX) analysis was used to characterize the membrane surface morphologically and examine the global chemical composition of the membranes and the distribution of the ILs within them.

Study of the freshly impregnated membranes showed that, in all cases, the ILs were homogeneously distributed, mostly filling the pores of the membranes although, in some cases, a small amount of excess of IL was located on the external membrane surface. Stability tests were performed by keeping the respective impregnated membranes immersed for a week in a diffusion cell including two independent compartments and using n-hexane/n-hexane as the respective feed and receiving phases. The SEM–EDX study of membranes after continuous operation showed that the ILs were still retained within the membrane pores and only small losses of the IL initially located on the external surface were observed. These observations are in complete agreement with the ionic losses determined by mass balance.