Solid samples, studies

Emanation thermal analysis (ETA) involves the measurement of the release of inert (usually radioactive) gas from a solid sample, as a function of temperature. The rate of such gas release is essentially an indication of the changes taking place in the sample, and a comparison of ETA data with those of other thermal analysis techniques, particularly TGA and evolved gas analysis (EGA), provides information on the microstructure of the sample material. However, most of the solid samples studied by ETA are spiked ... 

The same solid samples studied by FT-IR were analyzed by P MAS-NMR. For... 

The viscosity given by Eq. (3.98) not only follows from a different model than the Debye viscosity equation, but it also describes a totally different experimental situation. Viscoelastic studies are done on solid samples for which flow is not measurable. A viscous deformation is present, however, and this result shows that it is equivalent to what would be measured directly, if such a measurement were possible. 

There is an important difference between the two techniques in that photons, produced by XRF, can pass through a relatively large thickness of a solid sample, typically 4000 nm, whereas electrons can penetrate only about 2 nm. This means that AES is more useful in the study of solid surfaces, whereas XRF gives information referring more to the bulk of a solid or liquid. 

Almost any size solid sample can be studied in the SEM or EPMA The only limitation is the size of the specimen chamber, which is usually at least 10 cm in diameter. In a standard SEM, however, the x y translation is usually limited to 25 mm. In SEMs with an air lock for sample exchange, the maximum sample size may be only 3—5 cm in diameter. A highly polished surface is required for accurate quanti-... 

Another improvement that will allow quick simultaneous oligoelement homogeneity determinations in milligram samples can be expected by the use of solid sampling ETV-ICP-MS/AES and laser ablation ICP-MS which are now being studied in detail (Moens et al. 1995 Schiffer and Krivan 1999 Dobney et al. 2000). 

KuRFiiRST U, Grobecker KH, Stoeppler M (1984) Homogeneity studies in biological reference and control materials with solid sampling and direct Zeeman-AAS. In Schramel P, Bratter P, eds. Trace Element Analytical Chemistry in Medicine and Biology, Vol. 3, pp 591-601. de Gruyter, Berlin. 

INAA is well suited to study homogeneity of small samples because of its dynamic range of elemental sensitivity. The technique allows for the use of small solid samples, with the smallest usable sample size in the range of 0.5 mg to i mg as determined by handling and blank considerations. The INAA analytical procedure is well understood and characterized with mathematical relationships. Its analytical uncertainties can be sufficiently controlled and can be well determined for a particular procedure. This allows the calculation of the contribution of material heterogeneity to the uncertainty budget based on experimental data. 

Supercritical fluid extraction (SFE) is generally used for the extraction of selected analytes from solid sample matrices, but applications have been reported for aqueous samples. In one study, recoveries of 87-100% were obtained for simazine, propazine, and trietazine at the 0.05 ug mL concentration level using methanol-modified CO2 (10%, v/v) to extract the analytes, previously preconcentrated on a C-18 Empore extraction disk. The analysis was performed using LC/UV detection. Freeze-dried water samples were subjected to SFE for atrazine and simazine, and the optimum recoveries were obtained using the mildest conditions studied (50 °C, 20 MPa, and 30 mL of CO2). In some cases when using LEE and LC analysis, co-extracted humic substances created interference for the more polar metabolites when compared with SFE for the preparation of the same water sample. ... 

Work is in progress to validate the MAE method, proposed for EPA, in a multi-laboratory evaluation study. Nothing similar has been reported for additives in polymeric matrices. Dean el al. [452] have reviewed microwave-assisted solvent extraction in environmental organic analysis. Chee et al. [468] have reported MAE of phthalate esters (DMP, DEP, DAP, DBP, BBP, DEHP) from marine sediments. The focus to date has centred on extractions from solid samples. However, recent experience suggests that MAE may also be important for extractions from liquids. 

Obviously, direct SS-GF-ZAAS fulfils these criteria. A carefully performed homogeneity study using SS-GF-ZAAS was reported for the VDA CRMs (Cd in polyethylene) [137,223,224]. Solid sampling also allows analysis of high-purity materials (blank-free, low limits of analysis). 

Depth profiling of a solid sample may be performed by varying the interferometer moving-mirror velocity (modulated IR radiation). By increasing the mirror velocity, the sampling depth varies, and surface studies may be performed. Limitations do exist, but the technique has proven to be quite effective for solid samples [21]. In addition, unlike diffuse reflectance sampling techniques, particle size has a minimal effect upon the photoacoustic measurement. 

The dehydration, desolvation, or decomposition temperature of a compound can also be evaluated from an examination of discontinuities in the optical properties. These processes are most effectively monitored if the sample is immersed in an oil, since the evolution of gases normally accompanies these transformations. The evolution of gases is evident in the generation of gaseous bubbles from the solids under study. 

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