Sampling tools

Fluid samples may be collected downhole at near-reservoir conditions, or at surface. Subsurface samples are more expensive to collect, since they require downhole sampling tools, but are more likely to capture a representative sample, since they are targeted at collecting a single phase fluid. A surface sample is inevitably a two phase sample which requires recombining to recreate the reservoir fluid. Both sampling techniques face the same problem of trying to capture a representative sample (i.e. the correct proportion of gas to oil) when the pressure falls below the bubble point. 

The sidewall sampling tool (Sl/VS) can be used to obtain small plugs (2 cm diameter, 5 cm length, often less) directly from the borehole wall. The tool is run on wireline after the hole has been drilled. Some 20 to 30 individual bullets are fired from each gun (Fig. 5.35) at different depths. The hollow bullet will penetrate the formation and a rock sample will be trapped inside the steel cylinder. By pulling the tool upwards, wires connected to the gun pull the bullet and sample from the borehole wall. 

For assays of stable materials with wide ranges of tolerable error, sample handling is of little concern. For assays of labile materials, especially assays for purity or for minor components, controlled sample handling procedures need to be established. There are three potential ways in which a sample may become contaminated, namely by the sampling tools, sample containers, and degradation on storage. 

The fact that soil always contains water, or more precisely an aqueous solution, is extremely important to keep in mind when carrying out an analytical procedure because water can adversely affect analytical procedures and instrumentation. This can result in an over- or under-determination of the concentrations of components of interest. Deactivation of chromatographic adsorbents and columns and the destruction of sampling tools such as salt windows used in infrared spectroscopy are examples of the potential deleterious effects of water. This can also result in absorbance or overlap of essential analytical bands in various regions of the spectrum. 

Modification of the apparatus to accomplish automation is allowed by <711>. One example is hollow shaft sampling as illustrated in Figure 10 (15). This method is theoretically within the stated sampling location of the text of <711>, although there may be question about the concentration of sample surrounding the shaft. This and other sampling techniques, for example in-residence probes, are convenient sampling tools but should be properly validated. 

Galvanized sampling tools should not be used for trace element analysis. Usually from 20 to 25 cores are taken in a W pattern across the whole area. An alternative approach is to traverse the whole area in a zig-zag manner, sampling at random along different sections of the area (Scott et ai, 1971). The cores should be broken up and mixed well in a bucket, then about 200 g retained in a labelled polythene bag. 

Diffuse reflectance is an excellent sampling tool for powdered or crystalline materials in the mid-IR and near-IR spectral ranges. Heated reaction chambers for diffuse reflectance allow the study of catalysis and oxidation reactions in situ, and can evaluate the effects of temperature and catalyst behavior. Scratching sample surfaces with abrasive paper and then measuring the spectra of the particles adhering to the paper allows for analysis of intractable solids. Perhaps one of the greatest additional benefits is that this system is amenable to automation. 

Sampling tools are dedicated for each building and should be used accordingly. 

The next option (it seems to be the only one left after Fig. 2a and Fig. 2b but see Fig. 2d) is a route that negotiates the probability ravine (free-energy barrier) presented by the two-phase region (Fig. 2c). The extended sampling tools we discuss in the next section are essential here with their refinement in recent years, this route has become increasingly attractive. 

Sampling tools should be made of unpainted wood, polyethylene (plastic) or steel (unpainted spade). Field observation sheets for humus and soil are included in this manual (see Appendix 1). 

Groundwater samples collected with direct push sampling tools... 

Equipment blank is a sample of water collected from the surface of a decontaminated sampling tool to verify the effectiveness of a cleaning procedure. Equipment blanks are sometimes called rinsate blanks. They are collected as samples of the final rinse water from non-disposable sampling tools after they have been cleaned between samples. The field crew pours analyte-free water over the tool s surface that has come in contact with the sampled medium. The water is diverted directly into sample containers and analyzed for the project contaminants of concern. 

Ambient (field blanks) are sample containers with PTFE-lined septum caps filled with analyte-free water in the field to establish whether contamination could have been introduced into water samples from ambient air during sampling. The laboratory provides a bottle of analyte-free water, and the field crew pours this water from the bottle into a sample container in a manner that simulates the transfer of a sample from a sampling tool into a container. Ambient blanks are analyzed for the contaminants of concern that may be airborne at the site in order to assess the sampling point representativeness. 

Common to all water sampling procedures are several underlying issues related to the chemical reactions, which take place in the water samples between the time of collection and the time of analysis. Understanding the chemical processes that affect contaminants in a water sample is critical for selecting appropriate sampling tools and effective preservation techniques and in evaluating data quality. 

Non-disposable small sampling tools (bowls, spoons, etc.)... 

Muzzio FJ, et al. 1999. An improved powder sampling tool. Pharm. Technol. 23(4) 92-110. 

Control samples are a necessity in most soil sampling investigations. They should be sampled and processed the same way as other samples. Issues that may affect the validity of control samples are to ensure that the sampling tools are clean and not to treat sampling tools with oil or any other antirust agent. 

A few of the sampling tools used are blades, tubes, and augers (Byrnes, 1994). 

Yeats s criteria for the ideal sampling tool. They can be dedicated to individual monitoring wells to avoid cross-contamination between boreholes, they are portable, simple to use and relatively easy to clean. They are, however, not suitable for purging large volumes of water, and it can be difficult even with double-ended bailers to determine accurately where the sample was collected. Compared with other sampling devices, the operator is also more at risk of coming into contact with contaminated sample, especially when emptying the bailer (Fig. 3.1). 

Sampling tools (scoops and samples containers) should be manufactured from appropriate quality plastic materials or stainless steel. Operators should not wear or carry any jewellery or metallic apparel. 

In order to have this information, the parameters that define the level and type of pollution need to be evaluated. Therefore, scientists and technicians have to find the best chemical analytical tools that identify potential and existing pollutants. They also need to determine their properties, particularly those affecting the fate, transport, bioavailability, toxicity, and stability/degradation of the chemical constituents in a sample. Tools such as these may be considered a part of Environmental Chemistry. 

Failure to carry out these two steps properly contributes most often to bias in sampling. If part of the lot is inaccessible or the sampling tool cannot take the sample we have correctly defined, then getting a random sample is not possible. In the second part of the principle, we must ensure that we... 

The most common error in physically obtaining the sample occurs when the sampling tool cannot take the sample that has been properly defined. For example, an extraction error is produced by a retractable cross-stream sampler that goes only partway across the stream before returning to its idle position. This is in effect a grab sample since only one side of the stream is sampled. Any segregation across the stream will produce a biased sample. 

Figure 3.10 Correct sampling tool for sampling across a solid pile.

Contamination occurs when the sample lines are not purged (flushed) at least the length of the line to avoid getting old material, material that was drawn into the line when the last sample was taken. Sampling tools or sampling... 

---