The sampling procedure

The site of the soil sampling depends on the character of the terrain and purpose of the analysis. The choice of sampling sites in the locality investigated should include all the elements of the relief, i.e. valleys, lowlands, middle and top parts of the slope, terrain waves, etc. The sampling point should be situated at a typical site, at a sufficient distance from pollution sources (waste disposal areas, roads, industrial centres, etc.). 

The average soil sample is always taken from an area characterized by uniform cultivation (the same plant, fertilization, etc.). Smaller localities with considerably different soil characteristics are eliminated from sampling. The average area for taking one representative soil sample should be in the range 1 to 10 ha. Exceptions to this rule are areas contaminated during accidents. Surface and subsurface [5] sampling can be considered. 

The untreated sample represents the basic sample. In the case of agricultural soils, an amount of 0.5 to 1 kg of the sample is taken. The soil (earth), where the mineral portion is well mixed with organic matter (humus) is named the topsoil. When sampling the topsoil, it is necessary to consider the local conditions, i.e. characteristics of the environment of the sampling point, weather, vegetation, etc. 

When examining agricultural topsoils, a superficial layer (of about 5 cm) with residual amounts of the vegetation, etc. is removed by a shovel and under this layer, samples are taken from depths of 5 to 10 or 10 to 15 cm in the case of shallow or deeper topsoils, respectively. For meadow and pasture soils, tussocks are removed and the soil situated immediately under them is taken. 

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Estimations based on statistics can be made for total accuracy, precision, and reproducibility of results related to the sampling procedure being applied. Statistical error is expressed in terms of variance. Total samphng error is the sum of error variance from each step of the process. However, discussions herein will take into consideration only step (I)—mechanical extraction of samples. Mechanical-extracdion accuracy is dependent on design reflecding mechanical and statistical factors in carrying out efficient and practical collection of representative samples S from a bulk quantity B,... 

Regardless of the method of evaluating the solids mixture, the sampling procedure is vital. Often a sampling thief, or other special device, is used to remove samples from the mixture without excessive disturbance of the batch. If an easier method of sampling is obvious and will bring less contamination to the batch, it should be used. 

Chemical methods involve removing a portion of the reacting system, quenching of the reaction, inhibition of the reaction that occurs within the sample, and direct determination of concentration using standard analytical techniques—a spectroscopic metliod. These methods provide absolute values of the concentration of the various species that are present in the reaction mixture. However, it is difficult to automate chemical mediods, as the sampling procedure does not provide a continuous record of tlie reaction progress. They are also not applicable to very fast reaction techniques. 

The sampling procedure may involve a number of stages prior to the analysis of the material. The sampling stages are outlined in Fig. 5.1. 

It should be borne in mind that although it is possible to generalise on sampling procedures, all industries have their own established methods for obtaining a record of the quantity and/or quality of their products. The sampling procedures for tobacco leaves will obviously differ from those used for bales of cotton or for coal. But although the types of samples differ considerably the actual analytical methods used later are of general application. 

Samples that contain two phases present a special problem depending on the site of the materials of interest. If the substances are known to be associated with one phase only, the sample procedure is simply to separate the two phases by filtration or centrifugation and treat the sample as a liquid or solid sample depending on the phase that contains the materials to be determined. However, if the materials of interest are distributed between the two phases, some in solution and some adsorbed on the surface of the solid, then special extraction procedures will be necessary. 

Define the specimen(s) and the sampling procedure(s) to obtain a representative sub-sample of the materials to be examined. 

DP-6 over 3000 soil samples collected from several terrestrial field dissipation studies. The sample procedural recoveries using this method, conducted concurrently with the treated samples during soil residue analysis, are summarized in Table 5. This method was proven to be short, rugged, sensitive, and suitable for measuring residues in soil and sediment at levels down to 0.01 mg kg . The reproducibility of the methods also indicated acceptable method performance and, as a result, thousands of samples were analyzed using this methodology. 

An automated procedure to measure peak widths for peak capacity measurements has been proposed.35 Since peak width varies through the separation, the peak capacity as conventionally measured depends on the sampling procedure. The integral of reciprocal base peak width vs. retention time provides a peak capacity independent of retention time, but requires an accurate calculation of peak width. Peak overlap complicates automation of calculation. Use of the second derivative in the magnitude-concavity method gives an accurate value of the standard deviation of the peak, from which the base peak width can be calculated. 

In light of their high lipophilic properties, many OC compounds and some of their metabolites are detectable in adipose tissue however, this method cannot be applied to monitor occupationally exposed subjects on a routine basis because of the invasive nature of the sampling procedures. Because intact OC compounds and their metabolites are commonly found in blood and urine of the general population, comparison with appropriate reference groups or with individual pre-exposure values is recommended when surveying occupationally exposed workers. 

Field spikes with laboratory standards as well as spraying solutions were taken at a wide range of concentrations to determine the stability of the samples during both sampling and storage and possible contamination during the sampling procedure. Field blanks were also taken. 

The scheme given in Fig. 2.1 represents normal analytical procedures in off-line analysis. It contains all the steps that must be considered in principle. However, there could be reasons to reduce the course of action. Not in all cases is the analyst able to take samples by himself or check the sampling procedure. Sometimes he or she must accept a situation in which he or she has to receive a given sample (e.g., in extreme cases, extraterrestrial samples, autopsy matter). 

Sampling is always done for a specific purpose and (his purpose will determine, to some extent, the sampling procedure used. Canned food is examined for... 

There are international standards detailing the sampling procedures for both of these approaches [5-11]. 

The total variance in the final result (,v2ita ) is made up of two contributions. One is from variation in the composition of the laboratory samples due to the nature of the bulk material and the sampling procedures used ( ample). The other (Tanalysis) is from the analysis of the sample carried out in the laboratory ... 

The analytical variance can be determined by carrying out replicate analysis of samples that are known to be homogeneous. You can then determine the total variance. To do this, take a minimum of seven laboratory samples and analyse each of them (note that Sample characterizes the uncertainty associated with producing the laboratory sample, whereas sanalysis w h take into account any sample treatment required in the laboratory to obtain the test sample). Calculate the variance of the results obtained. This represents stQtal as it includes the variation in results due to the analytical process, plus any additional variation due to the sampling procedures used to produce the laboratory samples and the distribution of the analyte in the bulk material. 

Knowledge of spatial variations in bubble, drop, and crystal sizes is often desired or required, but extremely hard to obtain experimentally. Intrusive measuring and sampling probes may disturb flow and process locally. Taking samples may affect the sizes in the sampling procedure, samples may experience... 

As for the many surfactant metabolites, their distribution is often more homogeneous due to the loss of surfactant properties by the molecules. This would render the sampling procedure much simpler. 

Importantly, when interpreting the results obtained from a metabolic model, we always have to take into account the source and thus the reliability of the data that were used to parameterize these models. In the usual case that tissues and compartments are mixed in the sampling procedures, interpretation has to be limited to phenomena that are not influenced by the averaging effect. 

The olfactometric apparatus and the panel are in close connection with each other as shown in Table I whereas the sampling procedure is more or less apart from the apparatus... 

Only the guideline of Warren Springs, U.K., and the VDI-Guideline contain detailed descriptions of the sampling procedure. 

This review concentrates on the olfactometer The sampling procedures are reviewed by J.Hartung and the selection of panelist by M.Hangartner. 

However, attention must be paid to the sampling procedures in processes involving high temperatures and high degrees of humidity. Measurements indicate that such conditions may influence on ED50 values to some extent. 

Once the sampling procedure is accomplished, the sample container should be labeled immediately, to indicate the product, time of sampling, location of the sampling point, and any other information necessary for the sample identification. If the samples were taken from different levels of the storage tank, the levels from which the samples were taken and the amounts taken and mixed into the composite should be indicated on the sample documentation. 

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