Agitated soil measurement

Sethuramasamyraja B, Adamchuk VI, Dobermarm A et al (2008) Agitated soil measurement method fm integrated mi-the-go mapping of soil pH, potassium and nitrate contents. Comp Electrrai Agric 60(2) 212—225... 

Method 5021 describes the automated static-HS technique. Static HS has been introduced in this book from a theoretical viewpoint. A soil sample is placed in a tared septum-sealed vial at the time of sampling. A matrix modifier containing internal and/or surrogate standards is added. The sample vial is placed into an automated equilibrium headspace sampler. The vial s temperature is elevated to a fixed value that does not change over time and the contents of the vial is mixed by mechanical agitation. A measured volume of headspace is automatically introduced into a GC or a GC-MS. The method is automated and downtime is minimal. However, the cost of the automated system is appreciable. Contamination of the instru-... 

Hexachloroethane released to water or soil may volatilize into air or adsorb onto soil and sediments. Volatilization appears to be the major removal mechanism for hexachloroethane in surface waters (Howard 1989). The volatilization rate from aquatic systems depends on specific conditions, including adsorption to sediments, temperature, agitation, and air flow rate. Volatilization is expected to be rapid from turbulent shallow water, with a half-life of about 70 hours in a 2 m deep water body (Spanggord et al. 1985). A volatilization half-life of 15 hours for hexachloroethane in a model river 1 m deep, flowing 1 m/sec with a wind speed of 3 m/sec was calculated (Howard 1989). Measured half-lives of 40.7 and 45 minutes for hexachloroethane volatilization from dilute solutions at 25 C in a beaker 6.5 cm deep, stirred at 200 rpm, were reported (Dilling 1977 Dilling et al. 1975). Removal of 90% of the hexachloroethane required more than 120 minutes (Dilling et al. 1975). The relationship of these laboratory data to volatilization rates from natural waters is not clear (Callahan et al. 1979). 

Soil sorption coefficients are most often determined using a batch technique (Organization for Economic Cooperation and Development, 1983 American Society for Testing and Materials, 1993 2001), whereby a small quantity of the soil is agitated for a period of time (e.g., 18 hours) with an aqueous solution of the chemical under investigation the phases are then separated and the concentration of chemical measured in one or both of the phases. While in principle the method is simple, problems can arise due to, for example, incomplete phase separation, lack of time for equilibration, volatilization loss, and chemical instability. 

Textural analysis was conducted using temperature-controlled water baths and the Bouyoucos hydrometer method ( 8) with 2 modifications. First, soil samples were agitated for 20 seconds with plastic plungers instead of mixing the soil by inverting the container, and second, the clay suspension was not washed and sieved to determine fractional sizes. Organic matter percentages were determined with a dichromate reduction method (9). Electrical conductivity (ec) and pH were measured from the saturation extract of... 

Adsorption coefficients may be determined experimentally by batch equilibrium studies (e.g. OECD, 1983). Dispersions with a defined soil/solution ratio, containing each of several initial concentrations of the chemical, are agitated until equilibrium is achieved. The phases are separated by centrifugation and the compound s concentration is determined in the aqueous fraction. The reduction in concentration of the dissolved chemical in water is used as a measure of sorption. A desorption test is conducted consecutively and the adsorption isotherms are determined. Variability in the measured soil sorption coefficients may arise from ... 

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