Crop samples

In random samples of soil taken from five Alabama counties, only 3 of 46 soil samples contained methyl parathion. The concentration in these samples was <0.1 ppm (Albright et al. 1974). Aspartofthe National Soils Monitoring Program, soil and crop samples from 37 states were analyzed for methyl parathion during 1972. Methyl parathion was detected in only 1 soil sample, at a concentration of <0.1 ppm and taken from South Dakota, out of 1,246 total samples taken from the 37 states (Carey et al. 1979). In soil and sediment samples collected from a watershed area in Mississippi, methyl parathion was not detected in the soil samples. In three wetland sediment cores, however, measurable concentrations of methyl parathion were detected during application season (Cooper 1991). 

In contrast to the requirements for enforcement methods and to ensure sufficient quality of the generated data, validation data should be submitted for all types of crop samples to be analyzed. However, matrix comparability and a reduced validation data set may be considered where two or more very similar matrices are to be analyzed (e.g., cereal grain). A reduced sample set may also be acceptable (two levels, at least three determinations and an assessment of matrix interference) provided that the investigated samples belong to the same crop group as described in SANCO/825/00 (see also Section 4.2.1). 

Soil adhering to root and tuber crop samples must be removed with cold running water but samples should not be scrubbed with a brush. The samples should be dried in a clean room to avoid contamination. 

Sampling date, PHI, weight of sample and part of the crop sampled must be recorded as stated in the protocol. 

Having received the pre-weighed test item, preparation for its use in the field must be made. Ideally, water to be used in the dilution of the test item should be from mains water or a recognized source. The use of water from standing pools, rivers, etc., could potentially lead to problems with interference from contaminants during analysis of the crop samples. Depending on the formulation under test, the test item can be mixed in a variety of ways. First, the required water volume must be accurately measured. Approximately half of this amount can be poured into a clean bucket or similar mixing container. The temperature of the water should be noted at this point... 

Guidelines for the methods of sample collection of crop samples are detailed in the Codex Alimentarius, but generally in most instances crop samples should be representative of the crop being grown. As a general rule, the quantity of sample required is a minimum of 12 units or >1 kg of field sample, e.g., potato mbers, cabbages, etc. Samples selected should not be damaged or suffer from severe defects, disease symptoms, or other abnormalities. 

Samples collected from the field should ideally be placed in boxes in order to prevent damage to the crop sample and to aid storage, although this often depends on the freezing facilities of the organization concerned. Where samples are boxed, untreated samples should not be mixed with treated samples. When freezing, samples should be separated by space or by using separate freezers for treated and untreated samples. 

Shipping. Crop samples harvested for residue testing are usually shipped to the USA or Europe for analysis. Shipping requires the availability of an international... 

A 0.5-2-kg crop sample is cut into small pieces and homogenized thoroughly using a food processor. Rice grain is milled with an ultracentrifuge mill and sieved through a 42-mesh screen. The typical size of an analytical sample is less than 50 g. To prevent the decomposition of the anilide residues, crop samples should be frozen soon after collection and maintained frozen until analyzed. 

Owing to the potential for low levels of residues (parent plus metabolites) in crop tissues, the definition of dinitroaniline residues in crop samples is expressed as the parent molecule only. 

During the initial partition with hexane and water, the aqueous pH must not exceed 8. Carfentrazone-ethyl is extremely unstable under alkaline conditions and will rapidly degrade to C-Cl-PAc. At times, the workup of the crop samples, including the fortification step, should be completely separated for carfentrazone-ethyl and the acid metabolites, to avoid any possible interference from the parent compound. 

All crop samples should be prepared with a food chopper or Wiley mill to achieve a finely divided material. Soil and water samples should be well mixed to ensure a homogeneous sample. 

Transfer the concentrated crop sample extract (strawberries, rice grain, barley grain and rice straw) into a 50-mL separatory funnel with a small volume of water. Extract the solution three times with 10 mL of a chloroform-methanol (3 1, v/v). Dry the chloroform-methanol layer with a small amount (about 8 g) of anhydrous sodium sulfate on a glass funnel and transfer the dried solution to a 100-mL separatory funnel. 

High-performance liquid chromatographic determination Inject an aliquot (Vi) of the soil and crop samples into the HPLC system. 

Table 1 Diazinon concentrations in crop samples collected from European starlings (Sturnus vulgarus) following several applications to orchards in eastern Washington, USA...

Multi-residue methods (S19) to measure azole fungicides in crop samples... 

The author thanks the following scientists at DuPont Crop Protection and Battelle, Geneva Research Centres, for developing and validating some of the methods summarized in this article C.R. Powley for the soil method by HPLC/MS/MS J. J. Stry, SJ. Hill and PR Maliszewski for the water method by HPLC/MS/MS and K.M. Jernberg, B. Francon, M. Jetzer, C. Steiner, L. Dubey and H. Mattou for the independent laboratory validations of the Multiresidue Method 2 for crop samples. 

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