Dissolved species monitoring

Vne of the common problems encountered in studies of aqueous geo-chemistry and water pollution is proper identification of a particular species of an element or compound that may be present in the system. The use of electron spin resonance (ESR) spectroscopy to determine the presence and concentration of equilibrium and/or nonequilibrium metal species in natural water systems has not been adequately investigated. Coincidentally, Mn2, one of the easiest elemental species to detect by ESR, is also one of the dissolved species of considerable concern in problems related to heavy metal pollution and aqueous geochemistry. Furthermore, with proper design there exists the possibility of using electron spin resonance as the basis of a remote monitoring system for the detection of appropriate heavy metals in natural water systems. 

An Important application of the APM device in the area of chemical sensing is the indication of the presence, and In optimal cases the concentration, of specific dissolved species. We have reported the use of the APM device to monitor electrodeposition ( 1), electroless deposition (13), and the corrosion of metal films (22). In these applications, the device responds non-speclflcally to the presence of mass accumulated on (or removed from) the surface. Although such applications clearly demonstrate the use of the APM device to monitor surface mass changes while in direct contact with solution, they are not examples of specific chemical sensors. 

Hg(0), PHg, RGHg), wet deposition, throughfall, and litterfall, as discussed in the program to determine total ecosystem deposition (see Section 2.2.8). A summary of the measurements of Hg species that should be made in an intensive watershed Hg monitoring program is provided in Table 2.4. We envision that stream water measurements of total and dissolved THg and total and dissolved MeHg would also be made. 

The ideal HPLC detector should have the same characteristics as those required for GC detectors, i.e. rapid and reproducible response to solutes, a wide range of linear response, high sensitivity and stability of operation. No truly universal HPLC detector has yet been developed but the two most widely applicable types are those based on the absorption of UV or visible radiation by the solute species and those which monitor refractive index differences between solutes dissolved in the mobile phase and the pure mobile phase. Other detectors which are more selective in their response rely on such solute properties as fluorescence, electrical conductivity, diffusion currents (amperometric) and radioactivity. The characteristics of the various types of detector are summarized in Table 4.14. 

In the lower fan areas Se concentrations were monitored up to 400 pg/L. Similar historical distribution of soil Se content and shallow groundwater content indicate that dissolved selenium species were leached from saline soils by irrigation water. The drainage discharge of shallow groundwater and subsurface irrigation water was accompanied by increasing accumulation of Se in Kesterson Reservoir. 

Kerr el. al. [307] employed high performance liquid chromatography for the determination of uranium in groundwaters. The sample was passed through a small reversed phase enrichment cartridge, to separate the uranium from the bulk of the dissolved constituents. The uranium was then back flushed from the cartridge onto a reversed phase analytical column. The separated species were monitored spectrophotometrically after reaction with arsenazo(III). The detection limit was in the 1-2gg L 1 range with a precision of approximately 4%. 

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