Shimadzu GC-8A with ECD Detector:
Gas Chromatography
What is GC?
Gas Chromatography, or GC, is a separation of compounds in the gas phase based on the same types of interactions as in HPLC. Only volatile organic compounds can be used. Compounds are separated due to differences in their ability to partition, or transfer between the stationary and mobile phase. Usually this partition is based on polarity when doing GC analysis. The analysis is done at high temperature, usually 5-10oC higher than the highest boiling point in the mixture.
What does ECD mean?
ECD stands for Electron Capture Detector. This detector is very sensitive to halogenated compounds, as well as compounds with very electronegative functional groups such as nitro groups and peroxides. The detection limit of this detector for halogenatd compounds can be as low as the picogram level. This detector cannot detect compounds such as hydrocarbons, amines, and alcohols, making it very useful in quantifying herbicides and insecticides in groundwater and lakes.
The detector is made of a 63Ni source. 63Ni is a radioactive isotope, and emits electrons. As the effluent passes over the 63Ni, it will pick up these "loose" electrons if it has an electronegative functional group, such as chlorine or bromine. The detector sees the loss of electrons (ie a loss of current), and interprets it as a peak.
(Picture from http://elchem.kaist.ac.kr/vt/chem-ed/sep/gc/detector/ecd.htm)
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