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Selected Abstracts

Dual-asymmetry electrokinetic flow focusing for pre-concentration and analysis of catecholamines in CE electrochemical nanochannels

ELECTROPHORESIS, Issue 14 2009
Ren-Guei Wu
Abstract In this research, a technique incorporating dual-asymmetry electrokinetic flow (DAEKF) was applied to a nanoCE electrochemical device for the pre-concentration and detection of catecholamines. The DAEKF was constructed by first generating a ,-potential difference between the top and bottom walls, which had been pre-treated with O2 and H2O surface plasma, respectively, yielding a 2-D gradient shear flow across the channel depth. The shear flow was then exposed to a varying ,-potential along the downstream direction by control of the field-effect in order to cause downward rotational flow in the channel. By this mechanism, almost all of the samples were effectively brought down to the electrode surface for analysis. Simulations were carried out to reveal the mechanism of concentration caused by the DAEKF, and the results reasonably describe our experiment findings. This DAEKF technique was applied to a glass/glass CE electrochemical nanochip for the analysis of catecholamines. The optimum detection limit was determined to be 1.25 and 3.3,nM of dopamine and catechol, respectively. A detection limit at the zeptomole level for dopamine can be obtained in this device, which is close to the level released by a single neuron cell in vitro. [source]

Geochemical Tracers to Evaluate Hydrogeologic Controls on River Salinization

GROUND WATER, Issue 3 2008
Stephanie J. Moore
The salinization of rivers, as indicated by salinity increases in the downstream direction, is characteristic of arid and semiarid regions throughout the world. Historically, salinity increases have been attributed to various mechanisms, including (1) evaporation and concentration during reservoir storage, irrigation, and subsequent reuse; (2) displacement of shallow saline ground water during irrigation; (3) erosion and dissolution of natural deposits; and/or (4) inflow of deep saline and/or geothermal ground water (ground water with elevated water temperature). In this study, investigation of salinity issues focused on identification of relative salinity contributions from anthropogenic and natural sources in the Lower Rio Grande in the New Mexico-Texas border region. Based on the conceptual model of the system, the various sources of water and, therefore, salinity to the Lower Rio Grande were identified, and a sampling plan was designed to characterize these sources. Analysis results for boron (,11B), sulfur (,34S), oxygen (,18O), hydrogen (,2H), and strontium (87Sr/86Sr) isotopes, as well as basic chemical data, confirmed the hypothesis that the dominant salinity contributions are from deep ground water inflow to the Rio Grande. The stable isotopic ratios identified the deep ground water inflow as distinctive, with characteristic isotopic signatures. These analyses indicate that it is not possible to reproduce the observed salinization by evapotranspiration and agricultural processes alone. This investigation further confirms that proper application of multiple isotopic and geochemical tracers can be used to identify and constrain multiple sources of solutes in complex river systems. [source]

Nitrate behaviour in the groundwater of a headwater wetland, Chiba, Japan

HYDROLOGICAL PROCESSES, Issue 16 2004
Changyuan Tang
Abstract A wetland is an important part of the headwater in the discharge area of a basin. It controls not only groundwater discharge such as seepage or springs, but also the migration of chemical matter from the basin. In order to make clear how and where natural attenuation processes happen in wetlands, a typical headwater in Chiba, Japan, was chosen for an investigation of the behaviour of nitrate in groundwater. From the viewpoint of hydro-geomorphology, the wetland in the study site can be divided into three zones: the shallow water-table zone, the seepage zone, and the spring zone along the downstream direction. There were six piezometer groups; each group contained four piezometers, individually set at depths of 1, 2, 3 and 4 m. Major ions and ,15N of groundwater from piezometers, wells and springs were analysed. It was found that nitrate in groundwater mainly came from the fertilizers used in the upstream recharge area of the study site. When the groundwater moved up across the wetland, nitrate concentration in the groundwater decreased rapidly in the shallow water-table zone due to denitrification. Nitrate-free water can be found at the seepage zone. However, the behaviour of nitrate in the spring water was different from that in the seepage zone, since both dilution and denitrification processes were involved in the decrease of nitrate concentration in groundwater. In particular, the dilution process mainly controlled the decline of nitrate at the location where the nitrate-free groundwater flowing horizontally from the seepage zone mixed with the high-nitrate groundwater flowing upward before emerging as a spring. It was also found that denitrification only occurs suddenly in a narrow zone or a thin layer of the order of a few metres. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Temporal and spatial patterns based on sediment and sediment,water interface characteristics along a cascade of reservoirs (Paranapanema River, south-east Brazil)

LAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 1 2005
Adriana Jorcin
Abstract Physical and chemical characteristics of the sediments in a cascade of eight reservoirs located in the Paranapanema River (south-east Brazil) were analysed during two consecutive years during summer (January), autumn (April), winter (July) and spring (October) of 2000 and 2001, respectively. The granulometric texture, organic matter content and nutrient concentration (total nitrogen and phosphorus) were determined in the superficial sediment of 19 sampling stations, as well as the temperature, dissolved oxygen, pH, conductivity and redox potential in the bottom layer of the water column. Seasonal and spatial changes were observed for both years, especially for organic matter and nutrient concentrations. Three different areas could be identified along the river, which corresponded to the upper, middle and lower Paranapanema basin. The first area was characterized by an increase of nutrients and organic matter in the sediments and a decrease of temperature and dissolved oxygen in the downstream direction. The second one represented a region where fluctuations in nutrient and organic matter concentrations and a reduction in dissolved oxygen were observed. In the third area, there was an increase in nutrient and organic matter in the sediments and also an increase in temperature and dissolved oxygen towards the river mouth. The results of the principal components analysis, using water and sediments variables, showed the ordination of sampling stations by periods: wet (January,April) and dry (July,October) during 2000. This pattern was also verified during 2001, but with slight changes, probably due to the increase in the rains which would have produced certain homogenization effects along the river. [source]