Chlorofluorocarbons sampling

The Montreal Protocol of July 1987 resulted in an international treaty in which the industrialized nations agreed to halt the production of most ozone-destroying chlorofluorocarbons by the year 2000. This deadline was hastily changed to 1996, in February 1992, after a U.S. National Aeronautics and Space Administration (NASA) satellite and high-altitude sampling aircraft found levels of chlorine monoxide over North America that were 5i % greater than that measured over Antarctica. 

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. 

Karbiwnyk, C. M., Mills, C. S., Helmig, D., and Birks, J. W., Use of chlorofluorocarbons as internal standards for the measurement of atmospheric nonmethane volatile organic compounds sampled onto solid adsorbent cartridges. Environ. Sci. TechnoL, 37, 1002-1007, 2003. 

Brookhaven National Laboratories (BNL) has constructed an electron-capture detector capable of direct air sampling. The electron capture detector follows a catalytic reactor that contains H2 and Pd/Molecular Sieve 5A at 140°. This reactor effectively removes oxygen from the air sample stream by forming water. Additionally, chlorofluorocarbons are combusted and reduced to HCl and HF. These acids, along with HjO, are removed from the sample stream via a desiccant. However, such gases as SFg and per-fluorinated cyclic aliphatics [perfluorodimethyl-cyclobutane (PDCB), perfluoromethylcy do hexane (PMCH), and perfluorodimethylcyclohexane (PDCH)] survive the reactor and are detected via an electron capture device. These chemical compds survive due to their unusual thermal stability. BNL has demonstrated a lower limit of detection of these compds with their breadboard instrument (on a continuous sampling mode) of 0.1 parts per trillion (Ref 12)... 

An approximate order of response for the halogens is F < Cl < Br < I. Applications include trace analysis of environmental samples for chlorinated solvents, plasticisers, chlorofluorocarbon gases, pesticides and herbicides (DDT, 7BHC/lindane, aldrin), SFg tracer gas in flue gases and mine atmospheres, organometallics (lead tetra-alkyls), polynuclear aromatic carcinogens, NO and SO2 in chimney-stack gases. 

Mulls are used as alternatives to pellets. The sample (1 to 5 mg) is carefully ground into a suspension using a couple of drops of a mulling agent. This muU is pressed between two IR transmitting windows to form a thin film. Common mulling agents are Nujol (liquid paraffin), Fluorolube (a chlorofluorocarbon poly-... 

Methylene chloride has been the solvent of choice for many semivolatile analyses due to its high extraction efficiency, low cost, and specification by many regulatory methods. In the past chlorofluorocarbon solvents, such as trichlorofluoroethane, have been used for oil and grease analyses, because of their low human toxicity, and spectral qualities (i.e., no absorption at 2930 cm the wavelength generally used for sample measurement). However, owing to the detrimental effects of chlorofluorocarbons on stratospheric ozone, their use is being phased out. 

Fluorine compounds have many uses. One of the most notable of these is the manufacture of chlorofluorocarbon compounds known by the trade name Freon. These are chemical combinations of chlorine, fluorine, and carbon, an sample of which is dichlorodifluoromethane, CI2CF2. These compounds used to be widely employed as refrigerant fluids and blowing agents to make foam plastics they were also once widely used as propellants in aerosol spray cans. Uses of chlorofluorocarbons have now been phased out because of their role in destroying stratospheric ozone (discussed with oxygen, above). 

A 2.85 g sample of an unknown chlorofluorocarbon decomposes and produces 564 mL of chlorine gas at a pressure of 752 mmHg and a temperature of 298 K. What is the percent chlorine (by mass) in the unknown chlorofluorocarbon ... 

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