Soil samples extraction procedures

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 ... 

Tecator [20] has described a flow injection system for the determination of nitrate and nitrite in 2 mol/1 potassium chloride extracts of soil samples. Nitrate is reduced to nitrite with a copperised cadmium reductor and this nitrite is determined by a standard spectrophotometric procedure in which the soil sample extract containing nitrate is injected into a carrier stream. Upon the addition of acidic sulfanilamide a diazo compound is formed which then reacts with N-(l-naphthyl)ethylcncdiamine dihydrochloride provided from a second merging stream. A purple azo dye is formed, the intensity of which is proportional to the sum of the nitrate and the nitrite concentration. Nitrite in the original sample is determined by direct spectrophotometry of the soil extract without cadmium reduction. 

The solid phase extraction-HPLC method described by Matthijs and De Henau (1987) was used to determine LAS in sludge amended soil samples. The procedure was however adapted to use a Soxhlet extraction with methanol to give a more complete recovery of LAS from soil samples (generally >90% compared with 84% for the original reflux technique). A Soxhlet extraction time of 4 hours resulted in high recoveries of LAS from spiked soil samples An increase in extraction time up to 16 horns did not consistently improve the recoveries (Table 2). 

To date, little work has been cited in the literature with respect to arsenic speciation of polluted soil. A feasibility study on the identification and monitoring of arsenic species in polluted soil and sediment samples (Thomas etal. 1997) has been reported. In this study, polluted soil samples were extracted in phosphoric acid media using an open vessel microwave-assisted extraction system. The determination of arsenic species was investigated using an on-line system involving HPLC-ICP-MS system. The speciation was performed to identify As(III), As(V) and monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA). The proposed method had the potential to form the basis of a routine procedure for monitoring the behaviour of arsenic species in soils. This extraction procedure was recently applied to contaminated... 

The behavior of elements (toxicity, bioavailability, and distribution) in the environment depends strongly on their chemical forms and type of binding and cannot be reliably predicted on the basis of the total concentration. In order to assess the mobility and reactivity of heavy metal (HM) species in solid samples (soils and sediments), batch sequential extraction procedures are used. HM are fractionated into operationally defined forms under the action of selective leaching reagents. 

A soil sample was taken from a field, transported back to the laboratory by road and stored for three weeks prior to analysis. The analytical procedure consisted of drying the soil in an oven at 100°C for 24 h before the analyte was extracted using 200 cm of dichloromethane. This extract was reduced in volume to 200 til and a 20 p.l aliquot then analysed by HPLC. A calibration was set up by measuring the response from a number of solutions containing known concentrations of the analyte. The resnlt obtained from the unknown , after suitable mathematical manipulation, indicated the original soil sample contained 20 0.05 mgkg of the analyte. Comment on the accuracy of this result. 

Environmental monitoring of chloroacetanilides requires methods that have the capability to distinguish between complex arrays of related residues. The two example methods detailed here for water monitoring meet this requirement, but the method for metabolites requires sophisticated mass spectral equipment for the detection of directly injected water samples. In the near term, some laboratories may need to modify this method by incorporation of an extraction/concentration step, such as SPE, that would allow for concentration of the sample, so that a less sensitive and, correspondingly, less expensive, mass spectral detector can be used. However, laboratories may want to consider purchasing a sensitive instrument rather than spending time on additional wet chemistry procedures. In the future, sensitive instrumentation may be less expensive and available to all laboratories. Work is under way to expand the existing multi-residue methods to include determination of additional chloroacetanilides and their metabolites in both water and soil samples. 

Specifically for triazines in water, multi-residue methods incorporating SPE and LC/MS/MS will soon be available that are capable of measuring numerous parent compounds and all their relevant degradates (including the hydroxytriazines) in one analysis. Continued increases in liquid chromatography/atmospheric pressure ionization tandem mass spectrometry (LC/API-MS/MS) sensitivity will lead to methods requiring no aqueous sample preparation at all, and portions of water samples will be injected directly into the LC column. The use of SPE and GC or LC coupled with MS and MS/MS systems will also be applied routinely to the analysis of more complex sample matrices such as soil and crop and animal tissues. However, the analyte(s) must first be removed from the sample matrix, and additional research is needed to develop more efficient extraction procedures. Increased selectivity during extraction also simplifies the sample purification requirements prior to injection. Certainly, miniaturization of all aspects of the analysis (sample extraction, purification, and instrumentation) will continue, and some of this may involve SEE, subcritical and microwave extraction, sonication, others or even combinations of these techniques for the initial isolation of the analyte(s) from the bulk of the sample matrix. 

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. 

Residue analytical methods for neonicotinoids in crops, soil and water samples have been developed. The basic principle of these methods consists of the following steps extraction of the crop and/or soil samples with acetone or the other organic solvent, cleanup by liquid-liquid partition or column chromatography, and quantitative analysis by high-performance liquid chromatography with ultraviolet detection (HPLC/UV). Simple column cleanup procedures are used to improve the accuracy and sensitivity of these methods. 

Soil sample is extracted with a mixture of methanol and 0.1 M ammonium chloride. Acetamiprid, IM-1-2 and IM-1-4 residues are extracted with dichloromethane under alkaline conditions. After adding diethylene glycol, dichloromethane in the extract is removed by rotary evaporation, and the residue is subjected to a cleanup procedure using Florisil PR column chromatography and then with a packed Extrelut 20 column. 

A procedure that has been widely used for spray residues is the separation of the residue from the sample by extraction with an organic solvent, usually benzene. After most of the solvent has been removed, the residue is treated with sodium and isopropyl alcohol and the chloride ion is estimated by standard methods. Carter 10) has determined in this manner DDT residues on a number of crops, and he has recommended the adoption by the Association of Official Agricultural Chemists of the method as a tentative one for DDT 11). Koblitsky and Chisholm 42) have determined DDT in soil samples by the sodium-isopropyl alcohol procedure after removing the DDT by extraction with an azeotropic mixture of two volumes of benzene and one volume of isopropyl alcohol. 

In this study, 30 soil samples from rice farmland in Zhejiang province, in eastern China. We sampled the cultivation layer soils during rice harvest season. The soils are acidified and the average value of pH is 5.82. A sequential extraction procedure... 

In soil analyses, knowledge of the Eh-pH can be used in three ways. It will provide information as to the form or species of pollutant present (see also Chapter 6). It can also be used to determine which extraction procedure is best suited to extract a component from a soil sample. Potential changes in species, movement in the environment, and conditions suitable for bioremediation or natural attenuation can also be derived from this type of measurement. 

This type of extraction can be carried out in two different ways. A soil sample can be brought into the laboratory and extracted with relatively large amounts of water to try to determine its inorganic composition. The water-to-soil ratio can be either on a mass-to-mass basis or a volume-to-mass ratio. A one-to-one ratio is commonly used, although other ratios have been used. After a designated extraction time, with or without shaking, water is filtered from the soil and analyzed. A typical water extraction of soil is given in Procedure 11.1. 

It is possible to place a soil sample in an Erlenmeyer flask or other suitable container, add the desired extractant, stopper and shake for a specified period of time, filter, and analyze the extract for the analyte of interest. For an example of this type of extraction, see Procedure 12.1.4 The extract obtained from the simple extraction of 10 g of soil with water using a magnetic stirrer is shown in the right-hand flask in Figure 12.4 (see also Section 12.2.2). 

If a 1-g soil sample is extracted with 10 mL of extractant, then the component extracted is evenly distributed throughout the lOmL. This means the final result will need to be multiplied by 10 because the component was diluted 1 10 (this assumes an extractant density of lg/mL). This then is related back to the volume or mass of soil in the original sample, or it may be directly related back to the field. It may also be necessary to apply other conversion or correction factors, such as the percent water present in the original soil sample, depending on the procedure used. 

To study the chemical speciation of Aluminum in the solid - phase of the selected soil samples by selective chemical extraction procedures,... 

In this procedure the soil sample (spiked with isotopic marker compounds) is processed in a two-part enrichment procedure (Fig. 5.3). In part I, a mixture of the sample and sodium sulphate is subject to solvent extraction, and the extract is, in the same process, passed through a series of silica-based adsorbents and then through the carbon/glass fibre adsorbent. The extract passes through the adsorbents in the following order potassium silicate, silica gel, cesium or potassium silicate, silica gel and finally an activated-carbon... 

Mangani et al. [13] have described a method for determining extract chlorinated insecticides in soil. In this procedure a short column is packed with the soil sample. The insecticides in the soil are desorbed by a suitable solvent mixture chosen for its polarity characteristics. 

The sample extract from the soil sample is dissolved in 20ml of chloroform, using an ultrasonic cleaner to facilitate solution. This and a 10ml chloroform rinse are added to a dry lOg Florisil chromatographic column and eluted with an additional 110ml of chloroform. All the eluate is collected in a Kuderna-Danish unit and evaporated just to dryness, then the first 5g Florisil column clean-up procedure is followed. 

In order to determine chemical elements in soil, samples of the soil must undergo a solid-liquid extraction. Sometimes the extracts resulting from this procedure have analyte concentrations that are too high to be measured accurately by the chosen method. Therefore, they must be diluted. At the Natural Resources Conservation Service (NRCS) Soil Survey Laboratory in Lincoln, Nebraska, an automated diluting device is used. Using this device, the analyst accurately transfers aliquots of the extract and a certain volume of extraction solution to the same container. This dilutor may also be used to pipet standards and prepare serial dilutions. 

Sediment and soil samples are homogenized and extracted. Clean-up procedures are required prior to analysis by GC/ECD or GC/MS techniques (Lopez-Avila et al. 1992 Moseman et al. 1977 Saleh and Lee 1978 Tiernan et al. 1990). For sediment, soil, and sludge, recoveries were good (>85%) with sensitivity in the low ppb range (Moseman et al. 1977 Saleh and Lee 1978). Precision is good ( <6% RSD) (Saleh and Lee 1978). Analytical difficulties (unacceptable recovery not detectable using second capillary GC column) were reported (Lopez-Avila et al. 1992 Tiernan et al. 1990). 

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