Samples composite

Composite sampling is a way of reducing the cost of analysing large numbers of samples. A composite sample consists of two or more portions of material (collected at the same time) selected so as to represent the material being investigated. The ratio of components taken to make up the composite can be in terms of bulk, time or flow. The components of the composite sample are taken in proportion to the amount of the material that they represent. This type of sample may be appropriate when carrying out food surveys. The samples may, for example, be bulked in proportion to the amount normally consumed. 

Sampling is not important because errors involved in sampling can be controlled by  

Choose the most appropriate type of sample (representative, selective, random or composite) for the following parent materials. 

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Samples from municipal wastewater treatment plants and samples of industrial discharges often are collected as 24-h composites. Samples are obtained using an automatic sampler that periodically removes individual grab samples. The volume of each sample increment and the frequency of sampling may be constant or may vary in response to changes in flow rate. 

Sampling of biological tissue is done by removing the entire organ, which is then homogenized before smaller portions are taken for analysis. Alternatively, several small portions of tissue may be combined to form a composite sample. The composite sample is then homogenized and analyzed. 

Source sampling of particulates requites isokinetic removal of a composite sample from the stack or vent effluent to determine representative emission rates. Samples are coUected either extractively or using an in-stack filter EPA Method 5 is representative of extractive sampling, EPA Method 17 of in-stack filtration. Other means of source sampling have been used, but they have been largely supplanted by EPA methods. Continuous in-stack monitors of opacity utilize attenuation of radiation across the effluent. Opacity measurements are affected by the particle size, shape, size distribution, refractive index, and the wavelength of the radiation (25,26). 

The results of analyses of composite samples have been summati2ed (72). 

Ultrapure (triple distilled) mercury is commonly tested by evaporation or spectrographic analysis. In the former, a composite sample is evaporated and the residue weighed. In spectrographic analysis, a sample is dissolved and evaporated, the residue mixed with graphite [7782-42-5] and the emission spectmm determined with a spectrograph. 

The quantity of sample required comprises two parts the volume and the statistical sample size. The sample volume is selected to permit completion of all required analytical procedures. The sample size is the necessary number of samples taken from a stream to characterize the lot. Sound statistical practices are not always feasible either physically or economically in industry because of cost or accessibiUty. In most sampling procedures, samples are taken at different levels and locations to form a composite sample. If some prior estimate of the population mean, and population standard deviation. O, are known or may be estimated, then the difference between that mean and the mean, x, in a sample of n items is given by the following ... 

Average of 10-day composite samples collected during water year 1969. 

Example For the composite sample of 100 tensile strengths, what is the 90 percent confidence interval for i ... 

Composite Samples Obtained hy Multiple Sample Extractions. 19-8... 

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... 

The molybdenum, tungsten and tantalum concentration influence on LCD nickel-ferrous HRS resistance, used for gas turbine installations parts is investigated. The tests were carried out on modeling compositions. Samples were molded on the basis of an alloy of the ZMI-3C. The concentration of tantalum varied from 0 up to 5% with a step of 0,5%. The contents of elements were determined by a spectral method. 

Composite samples can be collected over an 8- or 24-hour period at half-hour or one-hour intervals from the regular effluent discharges such as from the pretreatment tanks. The volume of each sample will depend upon the variation in the discharge flow rate. 

The figure below shows the isothermal transformation diagram for a coarse-grained, plain-carbon steel of eutectoid composition. Samples of the steel are austenitised at 850°C and then subjected to the quenching treatments shown on the diagram. Describe the microstructure produced by each heat treatment. 

Step 9.4 Determine the Concentrations of Contaminants. Analyze wastewater to determine the concentration of contaminants. Take samples for laboratory analysis. Composite samples should be taken for continuously running wastewater. For example, a small volume - say, 100 ml - may be collected every hour through a production period of 10 hours, to gain a 1-liter composite sample. The composite sample represents the average wastewater conditions over that time. 

The TLCP used was a widely investigated one, Vectra A950, manufactured by Hoechst-Celanese. The PC was produced by Enichem under the tradename Sinvet 303. Table 3 lists the main properties of these materials according to the manufacturers. The materials were dried in a vacuum oven at 120°C for 4 h before processing. Prior to injection molding of the composite samples, two components were melt mixed by a ZSK, W P, Stuttgart, extruder with a constant weight ratio of PC-TLCP = 80 20 [23]. 

Table 4 Processing Condition and Mechanical Properties of PC-TLCP Composite Samples Injection Molded...

Kohli et al. [27], for instance, showed that the tensile modulus of a highly drawn PC-TLCP composite could be modeled effectively by the simple additivity rule of mixtures, while the compression molded composite samples with a spherical TLCP morphology had moduli according to the inverse rule. In both cases, the tensile modulus of the TLCP (Ei,c) itself was assumed to be a constant value determined from a tensile test of the pure TLCP samples. But whether or not the dispersed TLCP fibers and deformed droplets have the same modulus as the bulk TLCP samples remains a question. 

The three layers can be treated as an iso-strain parallel model in the flow direction. The total cross-section Atotai and the total tensile modulus totai E,) of a composite sample can be determined as follows ... 

Figure 24 Total modulus E, of PC-TLCP composite sample as function of the fiber modulus / for the four sample groups.

This constant value can be taken in turn into the composite functions to calculate the composite properties. A calculation result is illustrated in Fig. 25. For the four sample groups, the calculated layer moduli , are uneven in the cross-section within a composite sample group. The lowest value is still located in the core layer due to the lower deformation and, therefore, the lower... 

Figure 12 AES spectra of the W-SiC composite sample, (a) Schematic diagram of the sample (the shaded regions represent the reaction zone), (b) C and O line-scan profiles. The maximum PE noise is indicated by an error bar. (From Ref. 74.)...

Wu [353] who studied extruded fiber-filled composite samples established that the distribution of fibers along the radius of the specimen depended on the extrusion rate at low rates the fiber distribution is uniform, at medium rates the minimum of filler concentration occurs at 0.63 R (R is the extrudate radius) (in case of spherical particles this point corresponds to the maximum filler concentration) at high extrusion rates most of the fibers are concentrated about the flow axis and there are almost none on the extruded sample surfaces. 

Note on GMPs The assays are conducted on individual dosage units (here tablets) and not on composite samples. The CU test serves to limit the variability from one dosage unit to the next (the Dissolution Rate test is the other test that is commonly used). Under this premise, outlier tests would be scientific nonsense, because precisely these outliers contain information on the width of the distribution that one is looking for. The U.S. vs. Barr Laboratories Decision makes it illegal to apply outlier tests in connection with CU and DR tests. This does not mean that the distribution and seemingly or truly atypical results should not be carefully investigated in order to improve the production process. 

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