Bulk concentration trace

Certain trace substances such as selenium (IV) can be determined by differential cathodic stripping voltammetry (DPCSV). For selenium a rather positive preconcentration potential of-0.2 V is adjusted. Selenium (IV) is reduced to Se2", and Hg from the electrode is oxidised to Hg2+ at this potential. It forms, with Se2" on the electrode, a layer of insoluble HgSe, and in this manner the preconcentration is achieved. Subsequently the potential is altered in the cathodic direction in the differential pulse mode. The resulting mercury (II) peak produced by the Hg11 reduction is proportional to the bulk concentration of SeIV in the analyte. 

For sufficiently low coverages (such as those expected for low bulk concentrations, e.g. trace pollutants), the adsorption isotherms, equation (2), revert to linear ones ... 

The principal advantage of the ion microprobe (as opposed to the Auger microprobe) is the ability to obtain depth profiles for trace elemental species present in the analytical volume. The characterization of coal fly ash clearly illustrates this point (11-14). Auger detection limits are comparable to BSCA, and thus only elements with bulk concentrations greater than 1% by weight in fly ash (Si, Al, Fe, Ca, S, Na, K) can be... 

Membrane phase concentration of component i in the feed side, Cg, can be calculated from its bulk concentration by Henry s equation (Equation 5.8) provided it is present in trace amount in the feed solution. For higher concentration of component i, Cg can be obtained from experimental sorption data. Membrane phase concentration on the permeate side of component i, i.e., Cpi may be neglected due to the low pressure the activity of the component in the downstream side is very low. Thus, Equation 5.28 can be readily solved to calculate the theoretical flux and diffusion coefficient of i or j component employing any of the above equations relating the diffusion coefficient and concentration. Equations 5.14 through 5.25 depending on its best matching with the experimental data. 

GD-MS is of use for the direct determination of major, minor and trace bulk concentrations in electrically-conductive and semi-conductor solids down to concentrations of 1 ng/g. Because of the limited ablation (10-1000 nm/s), the analysis times especially when samples are inhomogeneous are long. It has been applied specifically to the characterization of materials such as Al, Cd, Ga, In, Si, Te, GaAs and CdTe. 

Since the trends in the behaviour of the trace elements are the subject of the present study, rather than the differences between individual trace elements, whether in relation to the SP, particle size or surface emichment, the adjusted bulk concentrations are preferred to the enrichment factors (EF) used in some earlier papers. 

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