Collection of a Representative Sample

There are many excellent books and articles describing collection and analytical methods for specific gases and vapors. Below, are listed only a few of the many possible sources that treat the subject of collection and treatment of gases and vapors [6-10], 

Walker, Handbook of Air Toxics Sampling, Analysis and Properties, CRC Lewis Publishers, 1995, 614 pp. 

8 1998 Annual Book of ASTM Standards, Section 11, Water and Environmental Technology, Volume 11.03 Atmospheric Analysis Occupational Health and Safety Protective clothing, ASTM, 1998, 1122 pp. 

Gas and Particle Phase Measurements of Atmospheric Organic Compounds, ed. D.A. Lane, Volume 2 in Advances in Environmental, Industrial and Process Control Technologies, ed. T. Vo-Dinh, Gordon and Breach, New York, 1999, 404 pp. 

This chapter presents an overview of the various methods used for collecting and treating liquid and sohd samples. These topics have been described extensively in a variety of manuscripts and review chapters in the literature [1—6]. This chapter contains two main sections, the first deals with obtaining a representative sample from either sohd or Hquid objects that cannot be analyzed in their entirety, and the second deals with the preparation of these samples for spectrometric analyses. 

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Thus, the collection of a representative sample becomes essential. For this reason, sample collection in this study was done for 2-4 days, and organics were extracted from 150-200 L of water. Although this method dilutes peak concentrations, the real concern with respect to micropollutants is the chronic effect (as opposed to an acute effect). Mutagenicity may result from several of the dissolved organics thus, the composite sampling procedure allows for the collection of a representative background matrix more closely associated with chronic-type exposure. 

Free-floating product or sheen present in the samples—the very nature of these samples prohibits the collection of a representative sample. 

At UMCDF, all discarded DPE suits are containerized and placed into a permitted storage area until treated at the site s MPF. Under the UMCDF permit, the physical state of the DPE suits prevents the collection of a representative sample. These materials are weighed and then treated in the MPF (ODEQ, 1997). 

The number of verticals to be sampled in a cross-section should relate primarily to the collection of a representative sample and secondarily to the volume of the sample required. If field measurements of specific conductance, temperature, pH, and dissolved oxygen show the water to be well mixed, then a sample obtained at a single vertical near the centroid of the flow may be assumed to be representative of the total flow. 

Collection of a representative sample as BOD tests are often carried out on sewage effluents and waste-water that are likely to be inhomogeneous, care should be taken to ensure the sample is as representative as possible. 

Many boilers are fitted with a heat exchanger-type water sampling coil that permits the collection of a representative and cooled BW sample. The design generally provides for a coil of copper or stainless steel (SS) fitted inside a small SS shell. The unit is fitted with gate valves to control the flow of cooling water and BW. 

Each new batch of media ingredients should be subject to quality control before agar or broth preparation. It is especially important to show that new batches of pig and horse serum can support the growth of a representative sample of species found infecting cell cultures, e.g. any two of M. orale, M. hominis, M. fermentans, M. arginini, M, hyorhinis or A laidlawii. The National Collection of Type Cultures (Colindale, London, UK) or the American Type Culture Collection (Manassas, Virginia, USA) may supply type strains, or wild-type strains may be used. Stock positive control cultures may be kept frozen at -70°C in mycoplasma broth. 

Five broad methodologies of data collection are currently in use in different countries around the world. These comprise personal visits to a representative sample of farmers and growers to collect information on what they have used (e.g. UK, USA) telephone calls replacing personal visits (e.g. Sweden) postal surveys of a representative sample of farmers and growers (e.g. The Netherlands) collation of sales statistics (many countries), or compulsory returns from all users of pesticides (e.g. California). 

The present paper reports on an investigation of preferences for potatoes based on stated preference data collected from a representative sample of 2,000 Italian households using the telematic network administered by AC-Nielsen S.p.A market research unit. The choices were derived by asking consumers to rate preferences for pairs of alternatives. 

In particle size measurements, one of the most inqKatant problems is the obtaining of a representative sample. It is the most difficult problem, and one that is often overlooked or undoestimated, especially for latexes. This problem increases in magnitude as the sample source increases in size, such that it is easier to obtain a representative sample from a 1-litre container than it is to obtain one from a 200-litre drum and, in turn, it is even more difficult to obtain a representative sample from a rail tank car. The reasons for this are obvious when one takes into consideration such factors as agglomeration, flocculation, settling, contamination and so forth. It is sufficient simply to call attention to this problem while collecting a sample for measurement as well as raising this question before measurements are made. 

Breast milk of well-nourished women normally contains about 50 xg reti-nol/dl (Moore, 1957). Because the lipid content and retinol concentration of breast milk increase as the breast is emptied, the selection of a representative sample poses a problem. Ideally, the total amount of milk in a breast should be collected and carefully mixed and an aliquot taken for analysis. Only in special circumstances, however, is this technique feasible. One procedure that has... 

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. 

Example of a systematic sampling plan for collecting samples from a lake. Each solid dot represents a sample collected from within the sampling grid. 

More attention to selecting and obtaining a representative sample. The design of a statistically based sampling plan and its implementation are discussed earlier, and in more detail than in other textbooks. Topics that are covered include how to obtain a representative sample, how much sample to collect, how many samples to collect, how to minimize the overall variance for an analytical method, tools for collecting samples, and sample preservation. 

A sample of hydrogen chloride gas, HC1, is being collected by bubbling it through liquid benzene into a graduated cylinder. Assume that the molecules pictured as spheres show a representative sample of the mixture of HC1 and benzene vapor ( represents an HCl molecule and O a benzene molecule), (a) Use the figure to determine the mole fractions of HCl and benzene vapor in the gas inside the container, (b) What are the partial pressures of HCl and benzene in the container when the total pressure inside the container is 0.80 atm ... 

The field phase of an LSMBS is critically important. Close monitoring of shoppers by field phase study management personnel is required, especially when a sampling plan includes frequent collections, such as weekly or bimonthly. Missed, delayed, or deficient commodity samples can throw a laboratory off schedule, which in turn can adversely affect both the timeliness and the quality of the analyses. Missed, delayed, or deficient samples can also affect the study outcome and interpretation, because a statistical design typically requires a certain number of data points, each represented by analysis of a commodity sample. 

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