In gas chromatography, electron capture detectors (ECD) are primarily used to detect which type of compounds?

Electron capture detectors (ECD) are particularly effective for detecting halogenated compounds, most notably chlorinated hydrocarbons. This method relies on the principle that certain compounds, especially those containing electronegative atoms such as chlorine, bromine, or fluorine, will capture electrons in the detector, resulting in a measurable signal.

Chlorinated hydrocarbon pesticides, like DDT, are examples of such compounds that have halogen atoms and are routinely monitored using ECD due to their low concentrations and high toxicity levels. The sensitivity of ECD to these compounds makes it the preferred choice in environmental testing and pesticide analysis.

While hydrocarbons and aromatic compounds can also be analyzed using gas chromatography, they do not have the same level of interaction with the electron capture detector as chlorinated hydrocarbons do, resulting in lower sensitivity. Aliphatic amines, although they can affect electron capture detection, do not typically fall into the scope of compounds for which ECD is primarily designed. Thus, chlorinated hydrocarbon pesticides stand out as the correct answer due to their specific reactivity and relevance in analytical chemistry involving ECD.