An electron capture detector (ECD) is a type of analytical instrument used primarily in gas chromatography to detect trace amounts of certain chemicals. It works by measuring the number of electrons captured from a sample as it passes through a radioactive source. This process generates a measurable current, which indicates the presence and concentration of specific compounds, particularly halogenated and other electronegative substances. ECDs are highly sensitive and can detect low levels of analytes, making them valuable in environmental monitoring and quality control in various industries. They are often used in conjunction with other detectors to provide a comprehensive analysis of complex mixtures.