Sample handling freeze drying

In this chapter, the results of past research are expanded because fiber cross sections were examined, rather than longitudinal views of fibers, and distributions of elements were obtained in addition to overall elemental spectra. Because the X-ray beam penetrates only a small distance into the surface of a sample (approximately 8-10 xm for a 25-kV excitation ), examination of a longitudinally mounted fiber produces elemental spectra of surface layers only. Such spectra may not be representative of the bulk of the fiber. In addition, this work improves upon past research in that the freeze-fracturing-freeze-drying EDS technique is suited to very small, fragile fiber samples (whether single fibers or small yam pieces), and is limited in size only in the operators ability to see and handle the samples. By using this procedure, compression of the fiber cross section and elemental redistribution are avoided. 

Freeze-drying is commonly used in conjunction with other concentration methods as the final step in isolating humic substances from water (Beck et al., 1974 Deinzer et al., 1975 Aldridge et al., 1976 Jolley et al., 1979 Thurman and Malcolm, 1981), and it is here that freeze-drying is most efficient. Samples of aquatic humic substances should be considerably concentrated and desalted prior to freeze-drying. The solid product obtained by freeze-drying can be easily handled and stored without fear of chemical degradation. 

The physical nature of the sample is important to the analyst. Freeze-dried materials are particularly difficult to handle. Their low density often makes it difficult to place them in the usual sample containers. The large... 

CAUTION The collection and handling of blood and other biological specimens requires great care because of the possible presence of transferable disease constituents, particularly from HIV or AIDS. Rubber gloves must be worn and often masks, as well. You will not draw blood or take other biological samples, nor handle samples from individuals. AH experiments are designed to use commercially available or synthetic materials that are safe (e.g., freeze-dried serum). Animal serum, such as horse serum or bovine serum, can be purchased fwww.sigma-aldrich.com). One experiment uses urine, and that can be either your own, from an animal, or synthetic. 

Bone samples for aluminium analysis have been taken from the iliac crest at the time of biopsy or at autopsy (Alfrey et al.. 1976 Maloney et al., 1982) and the specimen placed in an Al-free plastic container. Bone for histological staining is fixed in 10% buffered formalin (Maloney et al., 1982). Crapper et al. (1976) analyzed brain samples from specific areas of the cerebral cortex and from subcortical area. Alfrey et al. (1976) analyzed brain samples from frontal cortex. Whole brain as well as white and grey matter were analyzed. A description of how the specimen was handled before analysis was not provided. Crapper et al. (1976) transported and stored brain samples frozen in Al-free plastic containers and performed dissection from the frozen specimen in a dust-controlled room. All instruments and gloves were rinsed in aluminium-free water. At frequent intervals, this entire procedure was performed on standard homogenized freeze-dried brain powder to ensure little or negligible aluminium contamination. 

Fluids freeze-dried, tissue homogenized in Teflon ball-mill samples wet-ashed in sealed vessels for analysis. These elements are present at the mg/liter level or higher in biological samples and can be handled quite well by the technique. 

Lipids were separated by TLC according to Kates (7) and identified by comparison with standard lipids and by characteristic color reactions. Bands were scraped from TLC plates. For fatty acid analysis, samples from TLC plates or freeze-dried samples of Porohyridium were treated with methanol-acetyl chloride (95 5). Heptadecanoic acid was added and the mixture was handled up as previously described (8,9). Gas chromatographic analysis was performed on a SP-2330 fused silica capillary column at 200°. Fatty acids were identified by comparison with authentic samples and by GC-MS. 

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