Chemical changes, monitoring

From the technical and practical points of view, the efficient monitoring of rivers and water basins is a very difficult problem. This is due to the fact, that it is necessary not only to carry out a big number of water condition parameters measurements, but to follow the physical-chemical changes going on in the water as well. Such changes have a strong influence on the future state of the water basins. 

Tracers have been used to label fluids in order to track fluid movement and monitor chemical changes of the injected fluid. Radioactive materials are one class of commonly used tracers. These tracers have several drawbacks. One drawback is that they require special handling because of the danger posed to personnel and the environment. Another drawback is the alteration by the radioactive materials of the natural isotope ratio indigenous to the reservoir— thereby interfering with scientific analysis of the reservoir fluid characteristics. In addition, the half life of radioactive tracers tends to be either too long or too short for practical use. 

The chemical change in the Fricke dosimeter is the oxidation of ferrous ions in acidic aerated solutions. It is prepared from a -1 mM solution of ferrous or fer-roammonium sulfate with 1 mM NaCl in air-saturated 0.4 M H2S04. Addition of the chloride inhibits the oxidation of ferrous ions by organic impurities, so that elaborate reagent purification is not necessary. Nevertheless, the use of redistilled water is recommended for each extensive use. Absorption due to the ferric ion is monitored at its peak -304-305 nm. The dose in the solution is calculated from the formula... 

Measurements of thermal analysis are conducted for the purpose of evaluating the physical and chemical changes that may take place in a heated sample. This requires that the operator interpret the observed events in a thermogram in terms of plausible reaction processes. The reactions normally monitored can be endothermic (melting, boiling, sublimation, vaporization, desolvation, solid-solid phase transitions, chemical degradation, etc.) or exothermic (crystallization, oxidative decomposition, etc.) in nature. 

The unique appearance of an infrared spectrum has resulted in the extensive use of infrared spectrometry to characterize such materials as natural products, polymers, detergents, lubricants, fats and resins. It is of particular value to the petroleum and polymer industries, to drug manufacturers and to producers of organic chemicals. Quantitative applications include the quality control of additives in fuel and lubricant blends and to assess the extent of chemical changes in various products due to ageing and use. Non-dispersive infrared analysers are used to monitor gas streams in industrial processes and atmospheric pollution. The instruments are generally portable and robust, consisting only of a radiation source, reference and sample cells and a detector filled with the gas which is to be monitored. 

The ultraviolet (UV) rearrangement of polyarylesters and their related model compounds have been previously studied (20,21). The chemical changes which occur during the UV irradiation of styrylpyridine based ester and carbonate were investigated. The UV spectra of the p-VPPB and p,p -BVPDPC in 1,2-dichloroethane were monitored during the irradiation (Fig. 3 and 4). The maximum absorption for unirradiated p-VPPB was at 319 nm. After UV irradiation, the maximum peak shifted from 319 nm to 350 nm and the observed increased absorption in the... 

Kaplan, I.R., Galperin, Y., Alimi, H., Lee, R.P., and Lu, S.-T. Patterns of chemical changes during environmental alteration of hydrocarbon firels. Groundwater Monitor. Remed, 16(2) 113-124, 1996. 

Also, a chemist can use color intensity to monitor the progress of a chemical change. As reactants change to products, color changes occur. 

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