How to Purge and Trap Bromodichloromethane Water

Bromodichloromethane is a colorless, flammable liquid, generally formed as a by-product when chlorine is added to water supply systems to kill bacteria. The most common way that people are exposed to bromodichloromethane is through drinking water, although exposure may also occur through breathing chlorinated water vapor or through swimming in contaminated water. To date, bromodichloromethane is not linked to cancer in humans. In animals, however, high concentrations of bromodichloromethane have been shown to cause cancer of the liver and kidneys and affect the brain. Bromodichloromethane has been found at five of the EPA's 1518 National Priorities List sites. To analyze the bromodichloromethane at a site, the EPA uses a "trapping and purging" method.

Things You'll Need

• Inert gas (zero grade nitrogen or helium)
• Helium gas
• All glass 5-mL purging device
• Sorbent trap
• Thermal desorption apparatus connected to the gas chromatography apparatus

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Instructions

• 1

  Bubble inert gas (zero-grade nitrogen or helium) through a 5- or 25- mL sample of water suspected to be contaminated with bromodichloromethane. If the concentration of bromodichloromethane is expected to be very low (less than 1 percent) use the 25 mL sample to optimize the amount of bromodichloromethane to be trapped; use the 5 mL sample. This bubbling process is known as "purging," and it involves the conversion of aqueous bromodichloromethane to gaseous dichloromethane.

• 2

  Trap purged gas in a sorbent tube, a tube containing adsorbent solvents that will not alter the bromodichloromethane, that will trap the bromodichloromethane regardless of the presence of other solvents, and that will allow the bromodichloromethane to be easily extracted for analysis.

• 3

  Backflush the sorbent trap. When purging is complete, heat the sorbent trap to facilitate a rapid outflow of carrier gas and to desorb the purged components into a gas chromatographer. You now are ready to analyze the bromodichloromethane levels in water using gas chromatography.