Analysis methods soil extraction

Chromatography is a powerful, essential tool for the analysis of soils. Of the many forms of chromatography, gas and high-performance liquid chromatography are most commonly used in the analysis of soil extracts. Chromatographic and spectroscopic methods are almost exclusively referred to using... 

Within the last decade applications of new cidture-independent molecular tools based on PCR analysis of soil-extracted nucleic acids have provided unique insights into the conqiosition, richness and structure of microbial communities (58-61). Quantitative PCR methods will be used to estimate the abundance in soils of genes that encode atrazine-degradation enzymes, and by quantifying mRNA, their expression. Magnetic capture hybridization (MCH) followed by nested PCR could predict die potential of a soil to mineralize atrazine (62). In diis study, atzA gene copy number was quantified and found to be correlated... 

Supercritical fluid extraction (SFE) and Solid Phase Extraction (SPE) are excellent alternatives to traditional extraction methods, with both being used independently for clean-up and/or analyte concentration prior to chromatographic analysis. While SFE has been demonstrated to be an excellent method for extracting organic compounds from solid matrices such as soil and food (36, 37), SPE has been mainly used for diluted liquid samples such as water, biological fluids and samples obtained after-liquid-liquid extraction on solid matrices (38, 39). The coupling of these two techniques (SPE-SFE) turns out to be an interesting method for the quantitative transfer... 

Using established extraction and cleanup methods, followed by GC/FPD and GC/thermionic detection, Carey et al. (1979) obtained detection limits in the ppb range and recoveries of 80-110% in soil and 70-100% in plant tissue. Good sensitivity and recovery were maintained in a simplified extraction procedure of sediments followed by GC/FPD analysis (Belisle and Swineford 1988). Bound methyl parathion residues that were not extracted with the usual methods were extracted using supercritical methanol by Capriel et al. (1986). They were able to remove 38% of the methyl parathion residues bound to soil, but 34% remained unextractable, and 28% could not be accounted for. 

Analysis of soils and sediments is typically performed with aqueous extraction followed by headspace analysis or the purge-and-trap methods described above. Comparison of these two methods has found them equally suited for on-site analysis of soils (Hewitt et al. 1992). The major limitation of headspace analysis has been incomplete desorption of trichloroethylene from the soil matrix, although this was shown to be alleviated by methanol extraction (Pavlostathis and Mathavan 1992). 

The author is both a soil scientist and a chemist. He has taught courses in all areas of chemistry and soil science, analyzed soil, for organic and inorganic compounds, in both soil solids and extracts, using various methods and instruments, for 44 years. Introduction to Soil Chemistry, Analysis and Instrumentation, 2nd Edition, is the result of these 44 years of experience in two distinct climatic zones in the Philippines, four countries in Africa, and one in Central and one in South America. In the United States, this experience includes analysis of soils from all sections of the country. 

Saltar and Paasivirta [155] have described a method for the analysis in soils of MCPA (4-chloro-2-methyl phenoxy acetic acid) and two of its main metabolites, 4-chloro-o-cresol and 6-chloromethyl catechol by gas chromatography of their pentafluorobenzyl derivatives (Fig. 9.12). After derivitization of the residue extract, a clean-up procedure was applied. The best recoveries of compounds from soil were obtained when the extraction was performed by shaking with ether-acetone-heptane-hexane (2 1 1 1) from acidified soil and when the clean-up was done by thin layer chromatography (Table 9.17). Detection limits were in the range 20-25ng absolute. 

Tsukioka et al. [187] determined these contact herbicides in soil by mass fragmentography. The method is based on the reaction of l-benzyl-3-p-polytriazene with an extract of Frenock and Dalapon from strongly acidified sample solutions to form benzylated species. In the analysis of soil samples, steam distillation was applied prior to extraction. Recoveries were >92% and precision <5%. 

Hunt [34] has described a simple method of filtering soil extracts that eliminates the need for filter-funnels and receivers. It therefore reduces the risk of contamination and speeds up the procedure. It also offers a convenient means of obtaining filtrates in the field for subsequent analysis. 

For most analyses, it is necessary to separate the analytes of interest from the matrix (i.e., soil, sediment, and water). Extraction of analytes can be performed using one or more of the following methods (1) extracting the analytes into a solvent (2) heating the sample, as may be necessary to remove the solvent and for the analysis of volatile compounds and (3) purging the sample with an inert gas, as is also used in the analyses of volatile compounds. 

Stein VB, Narang RS. 1984. Chlorinated compounds and phenols in tissue, fat, and blood from rats fed industrial waste site soil extract methods and analysis. J Assoc Off Anal Chem 67 111-116. 

In soil analysis, the sample pretreatment varies depending on whether a total elemental analysis or an exchangeable cation analysis is required. In the former, a silicate analysis method (see below) is appropriate. In the latter, the soil is shaken with an extractant solution, e.g. 1 M ammonium acetate, ammonium chloride or disodium EDTA. After filtration, the extractant solution is analysed. Fertilizers and crops can be treated as chemical and food samples, respectively. 

Analysis of agrochemical samples from soils after extraction by Soxhlet methods are now replaced by analysis following supercritical extractions (Clement et al., 1997). 

Extraction of soils for analysis of die readily available nutrients include replacement of exchangeable cations by salt solutions, dilute acids, and dilute alkalies such as NaHCCh. Fluoride solutions ate employed to repress iron, aluminum, and calcium activity during the extraction of phosphorus. Extraction of the soil solution is effected by displacement in a soil column, often through the application of pressure across a pressure membrane. The soil solution is analyzed by conductance and elemental analysis methods. Also, the total elemental analysis of soils is made by Na2CC>3 fusion of the soil followed by classical geochemical analysis methods. 

In recent years antibiotics residues have accumulated in different environmental compartments. Fluoroquinolone antibiotics are strongly adsorbed by soil, and therefore their extraction requires exhaustive procedures, leading to complex extracts due to coextraction. Despite this the authors succeeded in selectively detecting the fluoroquinolones from crude soil extracts directly injected onto an MIP HPLC column and using UV detection [Fig. 2 (Fig. 6 of the original)]. Recoveries close to 100% were obtained for five fluoroquinolones. The analysis time was only a few minutes, so this method was found suitable for screening soil samples for the presence of fluoroquinolones. The individual fluoroquinolones were not resolved on the column. 

An extraction procedure performed by sonication method for dried marine sediments and soil followed by the analysis of the extracts using an electrochemical immunosensor based on magnetic beads and carbon screen-printed electrodes is described in the protocol (see Procedure 25 in CD accompanying this book). 

Some work on sediments is reported here in the belief that it may also be useful in the analysis of soil samples. Thus Asikainen and Nikolaides [33] have carried out a sequential extraction study of chromium from contaminated aquifer sediments and found that 65% of the chromium was extractable. Of this amount 25% was exchangeable, 11% was bound to organic matter and 30% was bound to iron and manganese oxide surfaces. Thomas et al. [34] also investigated the use of BCR sequential extraction procedures for river sediments, and found the method to work well. Real et al. [35] improved sequential extraction by optimising microwave heating. 

Online coupling of supercritical fluid extraction and high-performance liquid chromatography considerably decreases sample preparation time and analysis time [175]. Dunkers [128] showed that by using dilute dichloromethane as a static modifier, 20-30 minute supercritical fluid extractions gave results comparable to those obtained by conventional four-hour sampling methods in soil extractions. 

In addition to the above method, based on the use of pyrocatechol violet, Tecator also describes a flow injection analysis for determining 0.5-0.5mg/l aluminium in soil extracts based on the measurement of the chromazurol-aluminium complex at 570 nm [4,5]. 

Tecator Ltd. [16] have described a flow injection analysis method for the determination of 0.2 -1.4 mg/1 (as NH3N) of ammonia nitrogen in soil samples extractable by 2 M potassium chloride. The soil suspension in 2 M potassium chloride is centrifuged and filtered and introduced into the flow injection system for the analysis of ammonia (and nitrate) one parameter at a time. Ammonia is determined by the gas diffusion principle, in which a PTFE membrane is mounted in the gas diffusion cell. 

An early method for the determination of arsenic in soils is that of Forehand et al. [23]. This method is based on the selective extraction of arsenic(III) by benzene and analysis of the extract by atomic absorption spectrometry. Firstly the soil is allowed to stand with 9.9 M hydrochloric acid for 12 hours, and then the arsenic is reduced from arsenic(V) to arsenic(III) with stannous chloride and potassium iodide. Following adjustment to pH 9 with hydrochloric acid, the aqueous phase is extracted with benzene. The benzene extract is then treated with water and the water extract analysed by atomic absorption spectrometry at 193.7 nm. An average recovery of 88% of the arsenic present in sandy soils was achieved by this procedure. 

Smith and Lloyd [82] determined chromium(VI) in soil by a method based on complexation with sodium diethyldithiocarbamate in pH 4 buffered medium followed by extraction of the complex with methylisobutylketone and analysis of the extract by atomic absorption spectrometry (Evans R, City Analyst, Dundee, UK, private communication) [86]. Using this method, levels of chromium(V) of between 90 and 176 mg/1 were found in pastureland on which numerous cattle fatalities had occurred. 

Official methods have been published for the determination of exchangeable and extractable magnesium in soils [131]. Magnesium is extracted from the soil with 1M ammonium acetate and determined by atomic absorption spectrometry. The determination of magnesium in soils is also discussed under Multi-Metal Analysis of Soils in Sects. 2.55 (atomic absorption spectrometry), 2.55 (inductively coupled plasma atomic emission spectrometry), 2.55 (photon activation analysis) and 2.55 (ion chromatography). 

Akcay et al. [215] have shown that extraction of total strontium using an ultrasonic extraction procedure was not as good as was achieved using conventional extraction methods. Further work on the determination of strontium in soil is reported under Multi-Cation Analysis Methods including inductively coupled plasma atomic emission spectrometry (Sect. 2.55), emission spectrometry (Sect. 2.55), stable isotope dilution (2.55), and photon activation analysis (2.55). 

Hunt [340] has described a simple method of filtering soil extracts that eliminates the need for filter funnels and receivers. It therefore reduces the risk of contamination and speeds up the procedure. It also offers a convenient means of obtaining filtrates in the field for subsequent analysis. After shaking the soil suspension in the extraction bottle, a tube of filter paper folded about the centre to form a V with the open ends uppermost is inserted into the bottle. Clear filtrate collects inside the paper tube and aliquots are removed with a pipette. 

Van Staden [4,5] employed flow injection analysis coupled with a coated tubular solid-state bromide-selective electrode for the determination of bromide in soils. Soil-extracted samples are injected into 10 mol/1 potassium nitrate carrier solution containing 1000 mg/1 chloride as an ionic strength adjustment buffer. The sample buffer zone formed is transported through the bromide selective electrode onto the reference electrode. The method is applicable in the range 10-50 000 mg/1 bromide. The coefficient of variation of this method is better than 1.6%. 

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