Soil carbon tetrachloride extracts

Concawe [8] have described a method for the determination of aliphatic hydrocarbons in soil based on carbon tetrachloride extraction followed by infrared spectroscopy or gas chromatography. 

Hydrocarbon concentration has been measured by IR spectrophotometry, after a carbon tetrachloride extraction step [6]. The UV estimation (256 nm absorptiometry) has been tested compared to IR data for the 15 studied polluted soils (Fig. 15). The absorbance ratio A228 nm 256 nm can reflect, during a biological treatment, the composting degree of soils contaminated by petroleum hydrocarbons, as for PAH pollution. Quantitative data are collected in Table 9. 

Combine 50 g of the air-dried soil with 100 mL of acetone and shake the mixture with a mechanical shaker for 15 min. Filter the mixture through a fluted filter paper into a 500-mL flask. Wash the residue on the filter with 50 mL of acetone. Combine the filtrates and remove acetone by rotary evaporation. Transfer the residue with 150 mL of a potassium chloride solution into a separatory funnel, extract the solution with two portions of 50 mL of dichloromethane and collect the organic extracts in a flask. Filter the combined solvent extracts, together with the washings of the collecting flask, through anhydrous sodium sulfate into a 300-mL flask. Remove dichloromethane by rotary evaporation. Dissolve the residue in 10 mL of carbon tetrachloride. 

Workers at the Department of the Environment, UK [47], have described a procedure for the determination of methylmercury compounds in soils and sediments which involves extraction with a carbon tetrachloride solution of dithizone, reduction to elemental mercury then analysis by atomic absorption spectrometry. 

Based on a cost analysis performed at the U.S. Department of Energy s Hanford site, in Richland, Washington, PSVE was found to be a cost-effective method for remediation of soils containing lower concentrations of volatile contaminants. PSVE used on wells that average 10 standard cubic feet per minute (scfm) airflow rates was found to be more cost-effective than active soil vapor extraction for concentrations below 500 parts per million (ppm) by volume of carbon tetrachloride. For wells that average 5 scfm, PSVE is more cost effective below 100 ppm (D14489S, p. iii). For further details of this analysis, refer to Table 1. 

Most published methods are for analysis of crops and soil residues of the intact acaricides. Extraction has been done by stripping, blender or soxhlet. Extraction solvents have included petroleum ether, benzene, carbon tetrachloride, acetonitrile, diethyl ether, methanol and hexane/acetone. Clean-up steps have em -ployed liquid/liquid partitioning and adsorption on activated charcoal, activated charcoal/Florisil, Florisil, alumina and silica gel. Burke (14) reported that CB is not completely recovered from Florisil. Horn and coworkers (7) found that no clean-up was necessary when analyzing dog urine for CB using a Schecter-Haller procedure. For detection of residues, the colorimetric and UV methods have been replaced by gas chromatographic methods employing microcoulometric or electron capture detectors. 

The colorimetric procedures, though tedious and time-consuming, remain useful when the Mo concentrations in soils and plats are low. The stannous chloride-thiocyanate procedure, originally described by Marmoy (1939), and revised by Evans et al. (1950), Purvis and Peterson (1956), and Johnson and Arkley (1954), is one of the most widely used methods for determination of total Mo in soils. This procedure is based on formation of the colored complex Fe[MoO(SCN)5] produced by the reaction of Mo with an alkali thiocyanate and excess Fe in the presence of a reducing agent, stannous chloride. Isoamyl alcohol dissolved in carbon tetrachloride (Chapman and Pratt, 1961) is used to extract the complex from the aqueous phase. The Mo content is determined by comparison of the absorbance of the sample with appropriate standards. 

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