Identification Of Halocarbons Present In Samples
ECD Detectors
- Contain radioactive 63Ni and requires a license to operate
- Extremely sensitive to compounds with high affinity to thermal electrons such as organic compounds with Cl, Br, I, S, N, and O in their structure
- Very sensitive to O2, but also sensitive to H2S, N2O, and H2O
- Use ultra-pure N2 or Ar-CH4 mixture as the carrier gas, which is more difficult to use with capillary columns that work best with helium as the carrier gas
- Easily contaminated
- Some are sensitive to pressure changes associated with temperature ramping
- Calibration is non-linear. Multiple standards are required for calibration
The GC, column, pre-column, and cryogenic trap are optimized for the quantitative analysis of CFC-11, CFC-12, and CFC-113.
Other compounds that can be measured qualitatively during CFC analysis:
- Nitrous oxide
- Oxygen
- HCFC-22
- CFC-114
- Halon-1211
- Hydrogen sulfide
- Vinyl chloride
- Methyl chloride
- Methyl chloroform
- Methyl bromide
- Methylene chloride
- Chloroform
- Trichloroethylene
- Carbon tetrachloride
- Tetrachloroethylene
Identification of specific halocarbons should be confirmed by GC-mass spectroscopy since more than one compound can have the same or similar retention time. The retention time can vary as a result of changes in the oven temperature, the length of the analytical column, the carrier gas composition (N2, or Ar-CH4), and the carrier gas flow rate.