Specimens and Sampling

Guder, W.G. and Wahlefeld, A.W. (1983) Specimens and samples in clinical laboratory Sciences. In Methods of Enzymatic Analysis (ed. Bergmeyer, H.U.), 3rd edn. Verlag Chemie, Weinheim. 

The PHRR in the cone calorimeter is strongly dependent on the test setup and the specimen, as well as the intrinsic fire properties of the materials. To obtain comparable results, it is essential for the specimen and sample holder to be used as defined in the standard. This is illustrated in Figure 15.7, where the cone calorimeter HRR curves are compared with results using a modified sample holder.80 81... 

For corrosion resistance of a series of Sn RE TiO,, g (RE = Y, Yb, Gd, Sm, Nd, Pr, La) and Sri xTii yMyO3+5 (M = Nb, Ta) perovskites, the sintered specimens and sample powders were evaluated in the 50 wt % H2SO4 aqueous solution at 353K. Figure 4 shows the three-neck glass cell used for the corrosion test. After the corrosion test, dissolved A-site and B-site elements in the H2SO4 solution were measured using Inductively Coupled Plasma Mass Spectrometry (ICP-MS, Shimazu, ICPM-8500). 

The problem may be considered to become more difficult for specimens and samples which have actually to be regarded as raw data, or where reanalysis might be possible for some time even after the conclusion of the respective study. But on the other hand, there might be clear criteria to determine the end of usefulness of these archived materials. Let us consider the case of the test item sample the archiving of which is mandatory under GLP. At intervals, this sample might be analysed, and at some point of time the analytical chemist will determine that the sample is not useful anymore for its analytical purposes. This assessment will certainly mark the end of its required... 

Although the GLP Principles allow the disposal of specimens and samples, when their condition precludes further meaningful evaluation, the individual responsible for the archives has to pay attention also to the opposite clause of the Principles, namely the requirement that the storage conditions should preclude untimely deterioration. If for example, the jars containing preserved tissues cannot be sufficiently sealed, so that the preservative slowly evaporates, it lies in the responsibility of the archivist to periodically check these jars and to refill them with the respective preservative, if the need arises. Consequently, it would be considered a violation of the GLP Principles, if such specimens were just left to dry out, and the deteriorated specimens were then to be destroyed. 

R. Danzer, T. Lube, and P. Supancic, Monte-Carlo Simulations of Strength Distributions of Brittle Materials - Type of Distribution, Specimen- and Sample Size, Zeitschrift fur Metallkunde, 92, 773 -783,(2001). 

Specimen and sample As used in this chapter, the term specimen refers to the actual small object that is placed into the spectrometer. A sample is the as-received larger object from which an aliquot has been taken and prepared to give a specimen. For example, in a fertilizer analysis, the sample might consist of a 100-lb bag of fertilizer, whereas the specimen might be a 5-g aliquot pressed into a l -in.-diameter pellet. 

In many SEM applications, electrically non-conducting specimens, and samples containing moisture and other liquids such as oil, require to be examined. Conventional metal coating techniques to render the sample conductive are not always tolerable, and the normal SEM is too sensitive to vacuum degradation and contamination to allow... 

Danzer, R., Lube, T., and Supandc, P. (2001) Monte-Carlo simulations of strength distributions of brittle materials - type of distribution, specimen- and sample size. Z. MetaUkd., 92 (7), 773-783. 

Is polarization present in the specimen and sample beam Examine run data and graphs for anomalies. 

The phenomena we discuss, phase separation and osmotic pressure, are developed with particular attention to their applications in polymer characterization. Phase separation can be used to fractionate poly disperse polymer specimens into samples in which the molecular weight distribution is more narrow. Osmostic pressure experiments can be used to provide absolute values for the number average molecular weight of a polymer. Alternative methods for both fractionation and molecular weight determination exist, but the methods discussed in this chapter occupy a place of prominence among the alternatives, both historically and in contemporary practice. 

Fire test methods attempt to provide correct information on the fire contribution of a product by exposing a small sample to conditions expected in a fire scenario. Methods can be viewed in two ways the first entails the strategy of the fire test, ignition resistance or low flammabiUty once ignited the second addresses the test specimen, a sample representative of the product or a sample of a material that might be used in the product. Fire science has progressed markedly since the older test methods were developed and it is known that the basis for many of these tests is doubthil. Results from older tests must be used with great care. 

The contrast for specimen detail in the field of view is gready enhanced by darkfield illumination (10). The degree of contrast and sensitivity of detection of smaH-object details depend on the relative indices of the specimen and the mounting Hquid and on the intensity of the illumination. Darkfield illumination is not, however, a satisfactory solution for biologists who need direct transmitted light in order to observe specimens, especially stained specimens. It is, however, very usefiil in detecting asbestos fibrils that often exist in door tiles or water and air samples as 20-nm fibers (10 times finer than the resolution of an asbestos analyst s usual microscope) (11). Darkfield illumination yields an uimatural appearance and difficulties in interpretation hence, a need for better contrast methods stiU exists. 

As was cited in the case of immersion testing, most SCC test work is accomplished using mechanical, nonelecdrochemical methods. It has been estimated that 90 percent of all SCC testing is handled by one of the following methods (1) constant strain, (2) constant load, or (3) precracked specimens. Prestressed samples, such as are shown in Fig. 28-18, have been used for laboratory and field SCC testing. The variable observed is time to failure or visible cracldng. Unfortunately, such tests do not provide acceleration of failure. 

Compared to EDS, which uses 10-100 keV electrons, PEXE provides orders-of-magnitude improvement in the detection limits for trace elements. This is a consequence of the much reduced background associated with the deceleration of ions (called bremsstrahlun compared to that generated by the stopping of the electrons, and of the similarity of the cross sections for ioiuzing atoms by ions and electrons. Detailed comparison of PIXE with XRF showed that PDCE should be preferred for the analysis of thin samples, surfrce layers, and samples with limited amounts of materials. XRF is better (or bulk analysis and thick specimens because the somewhat shallow penetration of the ions (e.g., tens of pm for protons) limits the analytical volume in PIXE. 

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