Soil solution isolation methods

Although sampling and subsequently extracting analytes of interest is the standard method of soil analysis, sometimes it is advantageous to be able to sample and analyze the soil solution without addition of extractant. To do so, the soil solution can be collected in the field by collecting water that has percolated through a soil profile. Alternately, soil samples can be taken and the water isolated in the laboratory. In either case, the question as to the validity of the results of analytical analysis will depend on the status of the soil and the questions being asked. 

Various assay methods have been used to detect the presence of inhibitory substances. These include some of the classical tests used by investigators of growth-promoting substances—i.e., the various Avena coleoptile assays which utilize intact, decapitated, or isolated cylinders and the split pea stem test. Effects on seed germination and seedling shoot or root growth and development have also been measured in addition to other visible expressions of inhibition. Details of many of these tests have been compiled by Mitchell et al. (99). Tests have been carried out in Petri dishes, with various solution culture techniques, and by sand and soil culture. Effects so measured may or may not be similar to those obtained under field situations— i.e., the establishment of inhibition under controlled conditions pro-... 

In this method the soil extract and the blank and standards are evaporated almost to dryness by gentle heating and then cooled in an ice pack. Five millilitres of 80% sulfuric acid and then 1 ml of a 2% ethanolic solution of 3,4-xylenol are added. This solution is transferred to a separatory funnel with 80 ml ice-cooled distilled water. Toluene (10 ml) is added to the isolated toluene extract, and 5 ml of 1% sodium hydroxide is added to convert the phenol to the phenoxide. The lower aqueous phase is separated and evaluated spectropho-tometrically at 432 nm using matched silica cells with distilled water in the reference cell. 

Structural Studies of Humic Substances. Solid-state C NMR has played a major role in past studies of the chemical structure of humic substances isolated from soil as mentioned above. Recent studies have focused on the examination of humic substances from various environments to establish variabihties which might be indicative of structure and structural evolution.(29-34) Also, combined use of NMR with other analytical methods such as analytical pyrolysis, chemical degradative methods, and solution NMR studies has proved vduable in elucidating structural components. However, the complexity of humic substances has precluded all but inferred structures based on these combined studies. 

The method of isolation is often assumed in kinetic studies on soils and Mill constituents. Frequently, first-order kinetics for the solute of interest... 

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