Other Agricultural Samples

Other agricultural and biological chemicals can also usually be sampled using the methods described in this article. 

Flame emission spectrometry is used extensively for the determination of trace metals in solution and in particular the alkali and alkaline earth metals. The most notable applications are the determinations of Na, K, Ca and Mg in body fluids and other biological samples for clinical diagnosis. Simple filter instruments generally provide adequate resolution for this type of analysis. The same elements, together with B, Fe, Cu and Mn, are important constituents of soils and fertilizers and the technique is therefore also useful for the analysis of agricultural materials. Although many other trace metals can be determined in a variety of matrices, there has been a preference for the use of atomic absorption spectrometry because variations in flame temperature are much less critical and spectral interference is negligible. Detection limits for flame emission techniques are comparable to those for atomic absorption, i.e. from < 0.01 to 10 ppm (Table 8.6). Flame emission spectrometry complements atomic absorption spectrometry because it operates most effectively for elements which are easily ionized, whilst atomic absorption methods demand a minimum of ionization (Table 8.7). 

Lawrence [475] and Ryan and Lawrence [476] chromatographed insecticidal carbamates and other agricultural chemicals in the form of perfluorinated acyl derivatives. Of these they recommended HFB derivatives as most suitable. They prepared them by treatment with HFB anhydride in benzene in the presence of trimethylamine, as follows. A 15-jul volume of HFB anhydride and 0.4 ml of 0.1 M trimethylamine in benzene were added to 1—10 /rg of insecticide (dried extract of a food sample) in a 20-ml test-tube. 

Membrane based extractions are capable of complementing conventional techniques (liquid-liquid and solid phase extractions) in food and agricultural sample preparation. Their attractiveness in sample preparation is based on their selectivity and ability to tolerate samples with high organic content and/or dissolved solid. They can also be easily automated and interfaced to other separation techniques. However, despite these advantages, membrane based extractions especially SLM extraction and MMLLE techniques have not been applied much to food and agricultural samples as compared to PME techniques. 

The demonstration plot of the experimental site should be constructed to evaluate the effectiveness of phytoremediation. The field activities consist of site mobilization, plot layout an construction, and soil sampling combined with other agricultural practices designed secifically for phytoremediation and adapted for the conditions present at the site. The activities has to be conducted in accodance with the personal protective equipment, level of protection, action levels and other health and safety practices, i.e. hazard analysis general safety reccomendations evaluation of the mechanical, electrical, fire hazards, gas and power lines, heat stress, noise, chemical hazards. 

Quantification of an analyte in an agricultural sample relates to both the assay procedure and the sample preparation procedure. Conventional analyses frequently focus on total residues and may employ relatively harsh extraction procedures to remove bound materials from the soil or crop sample. The biological nature of antibodies requires that most immunoassays be run in aqueous systems at a pH near neutrality. If total residues are to be measured and extraction requires the use of organic solvents, strong acids, or strong bases the extracted materials must be dispersed in an aqueous medium prior to using an immunoassay. Moderate levels of methanol (<10i) and other water miscible solvents do not interfere with most immunoassays. 

Any systematic study of cell walls requires an a-D-galacturonanase to release pectic and other matrix components. Molecular structural studies have so far progressed that elaborate models showing the various polymeric constituents in juxtaposition have been generated. After enzymatic elimination of starch and protein, hydrolysis of the residual polysaccharide and estimation of the uronic acids and monosaccharides released furnish considerable information on the composition of agricultural samples. Partial depolymerization affords the complex, well-studied rhamnogalacturonans I and II (RG-I and RG-II). 

Table 19.3 Results of niacin determinations for milk samples. Niacin determinations by liquid chromatography-isotope dilution mass spectrometry (LC-IDMS) are compared to expected values for four milk samples. Expected niacin levels for milk are roughly 1 ppm, according to the USDA Nutrient Database for Standard Reference (US Department of Agriculture 2010) and results obtained for two commercial milk samples (Brands F and G) are a little under 1 ppm. The result for sample NFY0409F6 is about 30% lower, but is consistent with results obtained for other milk samples from the same source. In addition, the niaein level for NFY0409F6 was estimated by a standard additions experiment, the result from which is in agreement with the estimate from the normal LC-IDMS procedure. The level obtained for the reference material (RM) RM 8435 whole milk powder, reported on a dry mass basis, is in agreement with the reference value. Data are from Goldschmidt and Wolf (2007), with permission from the publisher.

For the standardization of different instruments, it should be noted that the stability of the standardization samples is not as critical as for the standardization of a single instrument over hme. When two NIR instruments must be standardized, the standardization samples need only be stable between the moment at which they are measured on the master instrument and the moment at which they are measured on the slave instrument. This period of time does not exceed a few minutes, if both instruments are located at the same place, and is not longer than a few days, if both instruments are far from each other. Therefore, less stable but more representative standardization samples can be used. For instance, Shenk and Westerhaus provide a set of 30 standardization cups containing different agricultural products that are representahve of most of the agricultural samples currently analyzed by NIR spectrophotometry [32,33]. These agricultural samples are probably not perfectly stable over several years, but because they can be considered as very stable over the space of a few days, they can therefore be used as standardization samples. 

Details about pesticides detected and their levels for typical samples containing multiple residues are shown in Table III. Domestic garland chrysanthemum contained diazinon, dimethoate, isoxathion above MRLs. Tomato was contaminated with phenthoate above MRL. It was found this pesticide was sprayed on the companion crop soybean . In domestic fruits, residues above MRL were not detected. Most of the samples were contaminated with both insecticides and fungicides. In imported products, residues with no MRLs, such as methamidophos and omethoate, were detected. Residue level of cypermethrin in baby pea exceeded 50% of MRL, which is set at low level comparing with other agricultural products... 

Pubhc concerns about pesticides in the diet of infants and children resulted in an expert committee convened by the U.S. National Academy of Sciences which devoted four years to the review of all available data. A consensus report was issued in 1993 (80). A number of recommendations for further work to more precisely define what constitutes the diet of infants and children were made. No risk could be estimated. The residue data reviewed by the panel were mainly from monitoring studies conducted by the PDA using multiresidue methods to analyze fresh produce and market basket samples collected from various geographic areas (81,82). These and other rehable scientific studies have demonstrated that relatively few food samples contain detectable residues. Most residues are far below estabhshed tolerances which are set above the maximum residue found in treated raw agricultural... 

Soils sampled at two sites in creek beds and drainage ditches in an agricultural area in the Point Mugu watershed near Oxnard, California, contained endosulfan at concentrations between 20 and 30 ppm. The majority of the other sites had much lower concentrations (Leung et al. 1998). 

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