Test organisms commonly used

COD is defined as the quantity of a specified oxidant that reacts with a sample under controlled conditions. The quantity of oxidant consumed is expressed in terms of its oxygen equivalence. COD is expressed in mg/L O2. In environmental chemistry, the chemical oxygen demand (COD) test is commonly used to indirectly measure the amount of organic compounds in water. Most applications of COD determine the amount of organic pollutants found in surface water (e.g. lakes and rivers), making COD a useful measure of water quality. 

Conversion coated or etched aluminium surfaces are generally free from organic contamination and easily wetted. A water break test is commonly used to establish that a clean surface has been generated. Such pre-treated surfaces have been described as forming a... 

Since the organisms are of marine origin the biotest should preferably be used for samples deriving from marine environments, such as sea water or marine sediment. Nevertheless, the tests are commonly used for freshwater samples as well (sewage or waste water treatment... 

Static Adhesion Tests for Organic-Based Yarns, Cords, and Fabrics. The most commonly used static adhesion tests are the H-test... 

Separation techniques may have to be applied if the given sample contains substances which act as interferences (Section 21.10), or, as explained above, if the concentration of the element to be determined in the test solution is too low to give satisfactory absorbance readings. As already indicated (Section 21.10), the separation methods most commonly used in conjunction with flame spectrophotometric methods are solvent extraction (see Chapter 6) and ion exchange (Chapter 7). When a solvent extraction method is used, it may happen that the element to be determined is extracted into an organic solvent, and as discussed above it may be possible to use this solution directly for the flame photometric measurement. 

At present, soil derived humic matter and fulvic acids extracted from freshwater are available commercially and are commonly used to test techniques for DOM detection and also used as model compounds for trace metal chelation studies. The results obtained using these model compounds are frequently extrapolated to the natural environment and measurements on "real" samples provide evidence that this DOM is a good model compound. In the past, some investigators also made available organic matter isolated from marine environments using C18 resins. While these compounds come from aquatic sources, this isolation technique is chemically selective and isolates only a small percentage of oceanic DOM. Reference materials are not currently available for these compounds, which inhibits study of the role they play in a variety of oceanographic processes. 

On the other hand, more recent studies have been designed to evaluate these hypotheses as they relate to (1) natural communities as contrasted to pure cultures, (2) cell densities more characteristic of natural ecosystems than those bacterial densities commonly used in tests of pure cultures, (3) synthetic compounds acted on by only a few rather than a diversity of microbial genera or species, and (4) compound concentrations which are characteristic of environmental pollutants rather than organic nutrients included in culture media. In general, all these explanations are related mainly to (1) proliferation of small populations, (2) presence of toxins, (3) predation by protozoa, and (4) appearance of new genotypes [ 101,104,106 -108,110,111 ]. 

Caco-2 model is easily affected by commonly used organic solvents or co-solvents [e.g., methanol, ethanol, polyethylene glycol (PEG), dimethyl sulfoxide (DMSO)] at relatively low concentrations (<1% v/v). Therefore, NCEs with poor aqueous solubility may not be adequately evaluated by this model. It has become a common practice in the pharmaceutical industry to test solubility of compounds before performing any other in vitro screens and eliminate NCEs with poor aqueous solubility, thus preventing false negatives due to this issue. 

A commonly used simple method for determining if there are any cracks or pinholes in microporous membranes is the so-caUed bubble point test. It has been used by many organic membrane manufacturers and users alike and is also being adopted by some inorganic membrane manufacturers. The method utilizes the Washburn equation... 

A commonly used method of sampling and analysis for volatile organic compounds In ambient air Is by concentration of the compounds on a solid sorbent such as Tenax and subsequent thermal desorption and GC/MS analysis of the collected compounds. The analysis phase, although not trivial, can be done well If proper care Is taken. However, the sampling phase of this process apparently Introduces artifacts and unusual results due to, as yet, unknown factors. A method to detect some sampling problems has been proposed and tested (7 ). This distributed air volume method requires a set of samples of different air volumes to be collected at different flow rates over the same time period at the sampling location. Each pollutant concentration for the samples should be equal within experimental error since the same parcel of air Is sampled In each case. Differences In results for the same pollutant In the various samples Indicates sampling problems. 

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