Representative sample obtaining

Table III Comparison of the results for five representative samples obtained with Equations [1]—[3] and [5] G (o) In MPa and the standard deviation s In... 

The sample shall be thoroughly representative of the crude oil in question, and the portion of the sample used for the sediment and water determination shall be thoroughly representative of the sample itself. If an automatic custody transfer (LACT) unit is involved, vigorous agitation of the sample container is required before the sample is transferred to the centrifuge tube or tubes. Only representative samples obtained as specified in Practices D 4057 or D 4177 shall be used for this test method. 

Only representative samples obtained as specified in Practices D4057 and D4177 shall be used for this test method. 

Laboratory Sample— J9lt only representative samples obtained as spedfied in Practices D 4057 or D 4177 for this test method. 

Laboratory Sample—OiAy representative samples obtained as qjedfied in Practice D 4057 and D 4177 shall be used for fiiis test method. 

Laboratory Sample—l tt sample of crude oil presented to the laboratory or test facility for analysis by this test method. Only representative samples obtained as specified in Practice D 4057 and Practice D 4177 shall be used to obtain the laboratory sample. 

Sampling saturated reservoirs with this technique requires special care to attempt to obtain a representative sample, and in any case when the flowing bottom hole pressure is lower than the bubble point, the validity of the sample remains doubtful. Multiple subsurface samples are usually taken by running sample bombs in tandem or performing repeat runs. The samples are checked for consistency by measuring their bubble point pressure at surface temperature. Samples whose bubble point lie within 2% of each other may be sent to the laboratory for PVT analysis. 

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. 

Much effort is made to obtain a representative sample from bulk dry soHds. This can be a difficult task for very coarse material and from large... 

Sampling Plan. The first step to assuring accuracy, ie, the conformity of the measured value to the tme or expected value (23), is to obtain a representative sample. Sampling may be the responsibiUty of either production or of QC. A written sampling plan approved by QC should be followed. It is the responsibihty of the QC unit to ensure that samples represent all the material under evaluation. 

In the case of l,4-ben2oquinone, the product is steam-distilled, chilled, and obtained in high yield and purity. Direct oxidation of the appropriate unoxygenated hydrocarbon has been described for a large number of ring systems, but is generally utilized only for the polynuclear quinones without side chains. A representative sample of quinone uses is given in Table 5. 

When a sample of ca 100 g has been obtained, a representative sample for use in size characterization equipment must then be taken. Some of the more modem methods of size characterization require as Htde as 1 mg of powder, thus obtaining a representative sample can be quite difficult. If the powder flows weU and does not contain too many fines, a device known as the spinning riffler (Fig. 4c) can be used. A spinning riffler consists of a series of cups that rotate under the powder supply. The time of one rotation divided into the time of total powder flow should be as large a number as possible. Although this device has been shown to be very efficient, problems can be encountered on very small (1 mg) samples, and the powder must be processed several times. Moreover, in order to avoid cross-contamination, cleanup after each of the sampling processes can be quite difficult. Furthermore, if the powder is cohesive and does not flow weU, the equipment is not easy to use. A siUca flow agent can be added to the powder to enable the powder to flow... 

Composite Samples Obtained by Multiple Sample Extractions Material flow streams are sampled in practice by combining extractions taken at successive time intei vals into a composite sample. Multiple increment collection to obtain representative composite sampfes for specified bulk-material flows is performed according to a... 

Selection of appropriate time intei vals for increment extractions relates to property variation (inhomogeneity) within material flow streams. Ten minute extraction intei vals are generally adequate to obtain suitably representative samples from material flows under practical circumstances. Precise determination of extraction intei vals consistent with individual apphcations can be calculatedthrough autocorrelation of historical sampling data, a statistical method described in references (Gy, Pitard). 

Particulates Procedures for testing a particulate source are more detailed than those used for sampling gases. Because particulates exhibit inertial effects and are not uniformly distributed within a stack, sampling to obtain a representative sample is more complex than for gaseous pollutants. EPA Method 5 (as shown in Fig. 25-32) is the most widely used procedure for determination of particulate emissions from a stationary source. In-stack samphng guidehnes are presented in EPA Method 17. 

Field Measurement Conditions Those gathering samples must be aware of the temperature, pressure, flamm ihty, and toxic characteristics of the samples for which they will be responsible. This is particularly important when samples are taken from unfamihar locations. Sample ports will have to be blown down to obtain representative samples. Liquid samples will have to be vented. Temperatures above... 

The results obtained for the proportion of a certain constituent in a given sample may form the basis of assessing the value of a large consignment of the commodity from which the sample was drawn. In such cases it is absolutely essential to be certain that the sample used for analysis is truly representative of the whole. When dealing with a homogeneous liquid, sampling presents few problems, but if the material under consideration is a solid mixture, then it is necessary to combine a number of portions to ensure that a representative sample is finally selected for analysis. The analyst must therefore be acquainted... 

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