Direct volatilization soil components

A number of techniques have been developed to directly volatilize soil components and contaminants and introduce them into the carrier gas of a gas chromatograph. Such procedures avoid the time and cost of extraction, cleanup, and concentration and also avoid the introduction of contaminants during the extraction process. However, these methods are not universally applicable and caution must be used when applying new or untested analyses or analytical procedures [2-5],... 

Before extraction, soil and sediment samples may be dried, for example, by freeze-drying — provided that volatile compounds are not to be analyzed — or by mixing with anhydrous sodium sulfate and extraction in a Soxhlet apparatus. It should, however, be noted that it has frequently been found advantageous to add low concentrations of water, and this is consistent with the finding that addition of water to dry soils inhibits sorption of PAHs (Karimi-Lotfabad et al. 1996). If wet samples are to be analyzed directly, acetonitrile, propan-2-ol, or ethanol may be employed first, and these may be valuable in promoting the chemical accessibility of substances sorbed onto components of the matrices the analyte may then be extracted into water-immiscible solvents and the water phase discarded. Alternatively, if the analyte is sufficiently soluble in, for example, benzene, the water may be removed azeotropically in a Dean Stark apparatus and the analyte then extracted with the dry solvent. Analytes may, however, be entrapped in micropores in the soil matrix so that, for example, recovery of even the volatile 1,2-dibromoethane required extraction with methanol at 75°C for 24 h (Sawhney et al. 1988). 

Our conceptual model divided the BDW lake basin into three land cover types (based on remote sensing data) (i) terrestrial, (ii) wetland, and (iii) lake (Fig. 3). Average annual mass movements for total mercury were calculated using the collected data [86]. Wet precipitation was the only source of mercury inputs considered to the terrestrial system accounting for 184 g (mercury deposited over land. The total outputs from the terrestrial system accounted for 372 g (o- = 36.7 g), of that, 35% (132 g, tr = 0.0 g) was incorporated into vegetation and, 13% (49 g, o-=0.0g) was volatilized from the soil surface. Although we were unable to measure mercury runoff directly, 191 g would be necessary in order to balance the inputs and outputs of the wetland component. 

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