Freezing, water preservation method

The method was extended from plants to include soils and waters by Milham ef al. (1970). They point out that nitrate reductase activity in fresh plant samples often causes a rapid decline in nitrate content, so samples collected from remote sites should be frozen in dry ice. A trace of chloroform was used to protect soil and water samples before freezing. We are now more aware of the harmful effects of chloroform inhalation and suggest immediate freezing without preservative and analysis within a few days as a safer alternative - especially with student projects. 

The osmotic dehydration does not reduce water activity sufficiently to hinder the proliferation of microorganisms. The process extends, to some degree, the shelf life of the material, but it does not preserve it. Hence, the application of other preservation methods, such as freezing, pasteurization, or drying is necessary. However, processing of osmotically dehydrated sani products is much less expensive and preserves most of the characteristics acquired during the osmosis. 

Numerous approaches, both physical and chemical, are recommended in the literature for the preservation of water samples for inorganic chemicals analysis. In particular, the significance of freezing, pasteurization, as well as the use of chemical preservatives such as acids, sodium hydroxide, chloroform, formaldehyde, or mercuric chloride as alternative techniques has been emphasized.810 Table 2.1 describes some recommended stabilization methods. 

Water molecules are constantly in motion, even in ice. In fact, the translational and rotational mobility of water directly determines its availability. Water mobility can be measured by a number of physical methods, including NMR, dielectric relaxation, ESR, and thermal analysis (Chinachoti, 1993). The mobility of water molecules in biological systems may play an important role in a biochemical reaction s equilibrium and kinetics, formation and preservation of chemical gradients and osmotic pressure, and macromolecular conformation. In food systems, the mobility of water may influence the engineering processes — such as freezing, drying, and concentrating chemical and microbial activities, and textural attributes (Ruan and Chen, 1998). 

A way to preserve vegetables vs. time is first to blanch them and afterwards to cool them in order to transform available liquid water into ice. This process is called "freezing" and has been established as an excellent method for preserving high quality in foods (Reid, 1983). Nucleation (formation of ice crystals) and crystal growth are the two major thermal events of the... 

The search for surface deposits that preserve anomalous oxygen isotope fractionations led fi om improbable sites such as the hyper-arid, super-hot Atacama Desert, Chile, to super-cold sampling pits dug in snow at the South Pole. The proxy dragnet focused on these remote sites because aridity and freezing are two viable methods for preserving water-soluble, direct products of atmospheric chemistry for detailed investigations. Anomalously fractionated... 

Methods commonly used for determining the elemental content of these biota samples include AAS, NAA, DPASV and ICP-AES. A pretreatment step is almost always necessary. The samples of urine should be acidified with a mineral acid or acetic acid for temporary preservation. The samples should, however, be freeze-dried or lyophilised for long term storage. It is possible to determine a number of elements in urine by diluting the samples with deionised water and aspiration into a flame or plasma. 

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