Chlorofluorocarbon determination

Over the next two years, Midgley and his group discovered and patented other chlorofluorocarbons and the halons, a class of bromofluoro-carbon compounds that are the world s best Are fighters. At the time, their remarkable stability seemed like an advantage. In the 1970s scientists were able to determine that CFCs and halons—which are so stable that they remain in the atmosphere for long periods of time—deplete the ozone layer 15 miles above Earth. 

Chlorofluorocarbon (CFC) compounds (Freons ) are important tracers of ocean circulation. Since CFC-11 and CFC-12 were released at different rates, their concentrations as well as their ratios can be used to determine when a water mass left contact with the sea surface over the 50 years since Freons were released into the atmosphere and taken up by the ocean. CFC-113 and carbon tetrachloride are being investigated as additional tracers. Picomole levels of CFCs dissolved in seawater are determined using a gas chromatograph equipped with an electron capture detector. The World Ocean Circulation Experiment (WOCE) Hydrographic Program calls for measurements with a precision and accuracy of 1% and a detection limit of... 

There have been extensive investigations into the kinetics of disproportionation reactions involving chlorofluorocarbon compounds.4-6 Phase equilibrium constants in relation to contact time and temperature have been determined and reported in various publications.1-3... 

This is a performance-based method that avoids the use of chlorofluorocarbon solvent. The method is applicable to aqueous matrices, using -hexane as the extraction solvent and gravimetry as the determinative technique. Because hexane is a hydrocarbon solvent, and if this solvent is employed for extraction, the method performance cannot be evaluated by IR measurement. The substances that may be determined by this method are relatively nonvolatile hydrocarbons, vegetable oils, greases, waxes, animal fats, and related materials. The method permits the use of other extraction solvents also, provided that the QC criteria are met. 

Methods for determining TPH in aqueous samples are discussed above in Section 3.3.1. The overall method includes sample collection and storage, extraction, and analysis steps. Sampling strategy is an important step in the overall process. Care must be taken to assure that the samples collected are representative of the environmental medium and that they are collected without contamination. There are numerous modifications of the EPA, American Public Health Association (APHA), and American Society for Testing and Materials (ASTM) methods discussed above. Most involve alternate extraction methods developed to improve overall method performance for TPH or replacement of the chlorofluorocarbon solvents. SPE techniques have been applied to water samples (Schrynemeeckers 1993). Solvent extraction methods with hexane (Murray and Lockhart 1981 Picer and Picer 1993) or methylene chloride (Mushrush et al. 1994) have been reported as well. 

Halocarbon Products, Inc.) or in a few other chlorofluorocarbons containing 2-3% by weight of a polar cosolvent such as methanol, trichloroacetic acid, or glyme. In these solvents, determinations of solution viscosity indicate that inherent viscosities (rjinh) of 0.4 or greater are necessary to obtain adequate vulcanizate properties. 

The following equation describes the reaction that produces hydrofluoric acid, which is used to make chlorofluorocarbons (CFCs). Determine the oxidation number for each atom in the equation, and decide whether the reaction is a redox reaction or not. If it is redox, identify which substance is oxidized, which substance is reduced, the oxidizing agent, and the reducing agent. 

At present, the concentration of chlorine atoms is mainly determined by destruction of synthetic chlorofluorocarbons, CFCs (see Section 3). 

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