Soil analysis extraction

This method can also be used to analyse soil samples. For instance, fenpropi-morph, which is a non-polar pesticide with good UV sensitivity but poor selectivity, has, after treatment, been determined in soil samples (31). In this example, an amount of soil was extracted overnight with acetonitrile this was then poured into a Buchner filter and rinsed with the same solvent. The acetonitrile solution was concentrated and, prior to LC analysis, the extract was diluted with water and 100 p.1 were then injected into the LC system. 

A 20-g sample of air-dried soil is extracted with 100 mL of ethyl acetate in a flask shaker for 45 min. After shaking, the extract is decanted and separated. The soil is re-extracted with 100 mL of ethyl acetate for 45 min. The combined soil extracts are filtered through a Whatman No 1 filter paper and the filter cake is washed with an additional 20 mL of ethyl acetate. The extracts are evaporated nearly to dryness, under vacuum, using a rotary evaporator. The residue is dissolved in an appropriate volume before GC analysis. ... 

Sample preparation consists of homogenization, extraction, and cleanup steps. In the case of multiresidue pesticide analysis, different approaches can have substantially different sample preparation procedures but may employ the same determinative steps. For example, in the case of soil analysis, the imidazolinone herbicides require extraction of the soil in 0.5 M NaQH solution, whereas for the sulfonylurea herbicides, 0.5M NaOH solution would completely decompose the compounds. However, these two classes of compounds have the same determinative procedure. Some detection methods may permit fewer sample preparation steps, but in some cases the quality of the results or ruggedness of the method suffers when short cuts are attempted. For example, when MS is used, one pitfall is that one may automatically assume that all matrix effects are eliminated because of the specificity and selectivity of MS. 

Sawhney BL. Extraction of organic chemicals. In Bartels JM (ed.), Methods of Soil Analysis Part 3 Chemical Methods. Madison, WI Soil Science Society of America and American Agronomy Society of Agronomy 1996, pp. 1071-1084. 

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. 

Both direct and indirect methods are used in studying soil chemistry. While in all cases direct methods are preferable, it is not always possible to make direct observations of all the chemical species, and physical and chemical changes of interest. Thus, it is often necessary to modify the soil before analysis. In many cases, it is essential to extract components before analysis can be carried out. It is also possible to obtain valuable information about the chemistry of soil by carrying out analyses that destroy all or a part of the soil matrix. A summary of analysis types and instruments commonly used in soil analysis is given in Table 8.1. 

The standard potentials of practically all oxidation and reduction reactions, especially those common in the environment and soil, are known or can easily be determined. Because of the specificity and relative ease of conducting voltammetric measurements, they might seem well suited to soil analysis. There is only one major flaw in the determination of soil constituents by voltammetric analysis and that is that in any soil or soil extract, there is a vast array of different oxidation-reduction reactions possible, and separating them is difficult. Also, it is not possible to start an investigation with the assumption or knowledge that all of the species of interest will be either oxidized or reduced. 

In both types of extraction, it is not certain that all the water or even a representative sample of the water is removed from soil. Water in small pores, cracks, or held at greater pressures that those applied to remove water will not be removed and their constituents will not be included in the analysis. However, both these methods find wide use in soil analysis. 

In soil analysis, HPLC is used much like GC in that soil is extracted and the extract, after suitable cleanup and concentration, is analyzed. One major difference between them is that HPLC does not require the components to be in the gaseous phase. They must, however, be soluble in an eluent that is compatible with the column and detector being used. A second difference is that both a syringe and an injector are used to move the sample into the eluent and onto the column. Detection is commonly by UV absorption, although RI, conductivity, and mass spectrometry are also commonly used. Conductivity or other electrical detection methods are used when analysis of ionic species in soil is carried out [3,78],... 

Gel electrophoresis has been applied to soil DNA and RNA extracts using procedures similar to those used in DNA testing for forensic analysis. CE has also been applied to the analysis of ionic species extracted from soil. While these processes show promise for the elucidation of valuable information about soil, neither is used for common, routine soil analysis [12-14],... 

The visible region of the spectrum (between 400 nm [violet] and 900 nm [red]), is used extensively in soil analysis in the colorimetric determination of components extracted from soil. Once extraction is complete and the extract has been filtered, it is analyzed for the components of interest by treating it with a reagent to produce a colored product. The amount of color is directly related to the amount of component present. 

An excellent example of this type of analysis involves the determination of phosphate in soil extracts. Soil is extracted with an appropriate extractant and added to a solution of acid molybdate, with which the phosphate reacts to produce a purple- or blue-colored solution of phosphomolybdate. Standard phosphate solutions are prepared, reacted with acid molybdate, and the intensity of the phosphomolybdate color produced is measured. A standard curve (also called a calibration curve) is prepared (see Section 14.10) from which the intensity of the color is directly related to the concentration of phosphate in the extract. 

Lopez-Avila et al. [59] used microwave assisted extraction to assist the extraction of polyaromatic hydrocarbons from soils. Another extraction method was described by Hartmann [60] for the recovery of polyaromatic hydrocarbons in forest soils. The method included saponification of samples in an ultrasonic bath, partitioning of polyaromatic hydrocarbons into hexane, extract cleanup by using solid-phase extraction, and gas chromatography-mass spectrometric analysis using deuterated internal standards. Polyaromatic hydrocarbons were thermally desorbed from soils and sediments without pretreatment in another investigation [61]. 

Mangani et al. [13] used Carbopack B columns to recover chlorinated insecticides in soil samples. These workers noted that, although the principles governing the adsorption and extraction process in the extraction in soil analysis are the same as those that govern liquid-solid chromatography, the main feature of a chromatographic column, i.e. separation efficiency, is almost completely absent. 

Thus, the columns used for the extraction should be regarded rather as an extraction apparatus than actual chromatographic columns. For soil analysis, a column is packed with soil. The soil behaves as an adsorbent that retains pesticides on its surface. These are eluted by a solvent mixture, that should be chosen for appropriate polarity characteristics. 

The suitability of the ELISA for soil analysis was initially tested by assaying a number of control soil samples, fortified after extraction and neutralisation with Paraquat in the range 10-300mg kgy1. The results in Table 9.19 were close to the expected values and thus confirmed that natural soil components did not interfere with the determination. These results justified the further refinement of the method for soil analysis. 

U.S. EPA Office of Solid Waste and Emergency Response, 1997, Analysis of Selected Enhancements for Soil Vapor Extraction. EPA-542-R-97-007, September. 

Method Performance. A blank sample, prepared using the same procedure as for the samples, was included with every five samples. PCB 28 and y-HCH were the only compounds detected in the blanks. Detection limits, calculated as mean blank +3 SD, were typically 2.3-13.3 pg/pF = 0.02-0.12 ng/g soil. Results were not blank corrected. Replicate analysis (the same soil sample extracted three times) was done for several samples. The relative standard deviation (RSD) for replicate analysis was always less than 20% (n = 3). Analytical recoveries were monitored with the aid of two recovery standards mirex for FI and 5-HCH for F2. The mean recovery for mirex was 100 ... 

Coutinho, J. (1997) Automated method for sulphate determination in soil-plant extracts and waters. In Hood, T.M. and Benton Jones, J., Jr (eds) Soil and Plant Analysis in Sustainable Agriculture and Environment. Marcel Dekker, New York, pp. 481 94. 

Mehlich, A. (1984) Mehlich 3 soil test extractant a modification of the Mehlich 2 extractant. Commununications in Soil Science and Plant Analysis 15(12), 1409-1416. 

The standard diluent must have the same matrix as the samples and the sampler wash solution. Therefore, use extraction solution for soil analysis. 

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. 

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