Sampling Plant Material

Except for extreme desert areas, most locations where munitions are buried will have plants. When the plants are growing directly over the munition, some of the explosive molecules released will certainly be drawn into the plant with its water intake. Whether these molecules are metabolized or concentrated has been studied for a few plants [17]. In either case, there may be opportunities for exploitation. 

If the explosive molecules are metabolized, the plant may produce some characteristic chemical signature that could aid in locating the source. If the molecules are concentrated, then it may be plausible to use the plant as a preconcentrator and sample the plant tissue to search for explosive compounds. 

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Two procedures of biomonitoring are available to estimate the pollution of aquatic locations passive biomonitoring by sampling plant material from natural sites and active biomonitoring using plant material exposed to the sites. 

Weight lo.s.s probe.s. Coupons for measuring weight loss are still the primai y type of probe in use. These may be as simple as samples of the process plant materials which have been fitted with electrical connections and readouts to determine intervals for retrieval and weighing, to commercially available coupons of specified material,... 

Maine purpose of our work was too developing methods for standardization of these products. Among methods traditionally used in analysis of plant material and herbal preparations HPTLC has shown to be fast, convenient and not to expensive. Because the goal of analysis is not to prove presence of certain compound, but to check if the product was made of proper raw material accomplishing technological conditions the best standard, in most cases, was properly prepared raw material sample. 

Various extraction methods for phenolic compounds in plant material have been published (Ayres and Loike, 1990 Arts and Hollman, 1998 Andreasen et ah, 2000 Fernandez et al., 2000). In this case phenolic compounds were an important part of the plant material and all the published methods were optimised to remove those analytes from the matrix. Our interest was to find the solvents to modily the taste, but not to extract the phenolic compounds of interest. In each test the technical treatment of the sample was similar. Extraction was carried out at room temperature (approximately 23 °C) for 30 minutes in a horizontal shaker with 200 rpm. Samples were weighed into extraction vials and solvent was added. The vials were closed with caps to minimise the evaporation of the extraction solvent. After 30 minutes the samples were filtered to separate the solvent from the solid. Filter papers were placed on aluminium foil and, after the solvent evaporahon, were removed. Extracted samples were dried at 100°C for 30 minutes to evaporate all the solvent traces. The solvents tested were chloroform, ethanol, diethylether, butanol, ethylacetate, heptane, n-hexane and cyclohexane and they were tested with different solvent/solid ratios. Methanol (MeOH) and acetonitrile (ACN) were not considered because of the high solubility of catechins and lignans to MeOH and ACN. The extracted phloem samples were tasted in the same way as the heated ones. Detailed results from each extraction experiment are presented in Table 14.2. 

In a recently pnblished example of betaxanthin analyses in a complex food matrix, 19 betaxanthins were assigned in yellow Swiss chard petioles. Mass spectrometric measnrements are even more helpfnl if nnknown betacyanin structures are to be elucidated. While betacyanic plant materials such as red beet and amaranth may still be commercially available for coinjection experiments and comparison with samples under investigation, it may be an easier task to first optimize pigment separation followed by mass spectrometric measurements. 

The aim of the analysis of cannabinoids in plants is to discriminate between the phenotypes (drug-type/fiber-type). Quantification of cannabinoids in plant material is needed if it will be used in medicinal appHcations, e.g., in C. sativa extracts. The ratio between A9-THC and CBN can be used for the determination of the age of stored marijuana samples [84]. 

Whilst for the analysis of plant material for cannabinoids both GC and HPLC are commonly used, in analytical procedures the employment of GC-based methods prevails for human forensic samples. Nonetheless, the usage of HPLC becomes more and more of interest in this field especially in combination with MS [115-120]. Besides the usage of deuterated samples as internal standards Fisher et al. [121] describe the use of a dibrominated THC-COOH (see 7.5). The usage of Thermospray-MS and electrochemical detection provide good performance and can replace the still-used conventional UV detector. Another advantage in the employment of HPLC rather than GC could be the integration of SPE cartridges, which are needed for sample preparation in the HPLC-system. 

The procedure described earlier for sample preconcentration can be easily extended for the online extraction of solid samples, e.g., powdered plant materials. Horizontal conbguration of the chromatographic plate in the chamber facihtates this procedure, because the sample to be extracted is then placed on a carrier plate at the begiiming part of the adsorbent layer (or in the scrapped channel of the adsorbent layer), which should be directed upward [15,26]. The chamber is covered with a narrow plate, and the development is started with a snitable extracting solvent. In some cases, it is advantageous to put the narrow plate directly on the adsorbent layer to press the sample to be extracted. Extracted components are preconcentrated on the adsorbent layer at the end of the narrow plate, as shown in Fignre 6.26 [15]. 

The literature includes a number of mis-matches, the following standing as examples for the many The use of bovine liver and other animal tissues for QC in the analysis of hmnan body fluids should not be considered by analysts. The matrix and the levels of trace elements do not match the levels to be analyzed, which may lead to serious errors. An even more severe mis-use was recently reported by Schuhma-cher et al. (1996) for NIST SRM 1577a Bovine Liver, which was used for QC in the analysis of trace elements in plant materials and soil samples in the vicinity of a municipal waste incinerator. Also recently, Cheung and Wong (1997) described how the quality control for the analysis of trace elements in clams (shellfish) and sediments was performed with the same material NIST SRM 1646, Estuarine sediment. Whilst the selected SRM was appropriate for sediments, its usefulness as a QC tool for clams is difficult to prove see also Chapter 8. This inappropriate use is the more mystifying because a broad selection of suitable shellfish RMs from various producers is available. 

The second requirement is that enforcement methods for food must be validated by an independent laboratory [independent laboratory validation (ILV)]. The sample set is identical with the general sample set (see Section 4.1). If the method is identical for all four crop groups (mentioned at the beginning of the section), it may be sufficient to perform the ILV for plant materials with a minimum of two matrices, one of them with a high water content. In the case of food of animal origin, the ILV should be performed with at least two of the matrices milk, egg, meat, and, if appropriate, fat. 

Plant material. Weigh 25 g of the chopped and frozen sample into a blender jar. To check recoveries, spike the fortification samples with the appropriate volume of metabolite standard at this point. Add 200 mL of acetonitrile-water (4 1, v/v) to the jar, and blend the sample at medium speed for 5 min. Filter the extract through a Buchner funnel fitted with a glass-fiber filter pad into a 500-mL round-bottom flask containing 10 drops of Antifoam B and 3 mL of 10% aqueous Igepal CO-660 (nonionic surfactant). The flask is connected to the Buchner funnel by means of an adapter suitable for applying vacuum to the system. 

Soil samples are prepared by removing stones and plant materials and passing through a 5-mm sieve. 

The major metabolite of pyraflufen-ethyl in plants and soils is E-1 (ester hydrolysate). E-2 (phenol derivative) and E-3 (methylated E-2) are also detected as major metabolites in soils. The target analytes are considered to be pyraflufen-ethyl at least in plant materials, pyraflufen-ethyl, E-1, E-2 and E-3 in soils and pyraflufen-ethyl and E-1 in water samples. 

Sample extracts are cleaned up with a cartridge column before the acetylation of E-2 to E-16 and of E-1 to E-15. The final cleanup, plant material and soil samples are analyzed by gas chromatography (GC)/MSD. The GC/NPD method is applicable to water samples. 

All of the compounds (pyraflufen-ethyl and its metabolites) are converted to E-2 and quantified as the total toxic residue of pyraflufen-ethyl. The conversion to E-2 is carried out by oxidative decomposition with concentrated sulfuric acid. The reaction mixture is extracted with a solvent and subjected to simple cleanup, followed by GC/NPD analysis. This method is rapid and simple compared with the Multi-residue analytical method , and has wide applicability to different varieties of the samples, such as plant materials, soils and water, with only minor adjustment of the analytical method. 

Sample preparation techniques vary depending on the analyte and the matrix. An advantage of immunoassays is that less sample preparation is often needed prior to analysis. Because the ELISA is conducted in an aqueous system, aqueous samples such as groundwater may be analyzed directly in the immunoassay or following dilution in a buffer solution. For soil, plant material or complex water samples (e.g., sewage effluent), the analyte must be extracted from the matrix. The extraction method must meet performance criteria such as recovery, reproducibility and ruggedness, and ultimately the analyte must be in a solution that is aqueous or in a water-miscible solvent. For chemical analytes such as pesticides, a simple extraction with methanol may be suitable. At the other extreme, multiple extractions, column cleanup and finally solvent exchange may be necessary to extract the analyte into a solution that is free of matrix interference. 

Positive controls demonstrate adequate amplification and may be used to quantify the sensitivity of the reaction. One approach is to add known amounts of reference material [e.g., soybean and corn powder containing 0.1% (w/w) genetically altered material] to the standard PCR and to run these concurrently with the test samples. Plant genomic DNA and GMO genomic DNA may also be used as positive controls in the PCR. 

Hymexazol has such a high vapor pressure that the sample extract should not be concentrated to dryness without a keeper such as polyethylene glycol. After homogenization of plant materials, the extraction procedures should be carried out promptly without long-term storage. 

Mepronil in plant materials is extracted with aqueous acetone. Rice straw sample is extracted with aqueous methanol. Soil samples are refluxed with alkaline methanol. After filtration, the solvent is removed by evaporation under reduced pressure and... 

Untreated control samples were fortified with mepronil. The fortification levels were 0.05-0.25 mg kg for plant materials and 0.005-0.05 mg kg for soil. The following recoveries were obtained 93-95% from rice grain 93-99% from rice straw 86-96% from grape 99-103% from leek 90-110% from lettuce 96-106% from sugar beet (root) 92-100% from sugar beet (leaf) 91-96% from kidney beans 96-100% from string beans and 86-98% from soil. The limit of detection is 0.005 mg kg for plant samples, except for rice straw and soil materials, and 0.01 mg kg for rice straw. 

Plant material should be added to a disk mill (grain or seed matrices) or a vertical batch processor (all other matrices). Add an equal portion of pelletized dry-ice to the sample (vertical processor only). Macerate the plant sample (or sample -I- dry-ice) until a homogeneous mixture is obtained. Soil samples should be well mixed or... 

Plant material is homogenized in acetone followed by addition of water. The filtered extract is diluted with acetone-water (2 1 v/v) and filtered through a syringe filter. The sample extract is diluted 1 1 with a deuterated azinphos-methyl internal standard and analyzed using LC/MS/MS in the positive-ion selected reaction monitoring (-I-SRM) mode. 

Second cleanup Transfer the above carbon tetrachloride solution into a glass column packed with 7 g of silica gel saturated in carbon tetrachloride. Rinse the column, first with 2 mL of carbon tetrachloride and then with 35 mL of hexane-ethyl acetate (17 3, v/v). Elute benfuracarb with 30 mL of the same hexane-ethyl acetate solution. Concentrate the eluate to near dryness by rotary evaporation and prepare the GC/HPLC-ready sample solution by dissolving the residue either in benzene for plant material or in acetonitrile for water and soil. 

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