How do FID and ECD detectors differ in principle and selectivity in GC?

How do FID and ECD detectors differ in principle and selectivity in GC?

• A. FID detects ions produced by combustion of organic compounds; ECD detects electronegative species via electron capture; ECD is highly selective for halogenated compounds.
• B. FID detects UV absorption; ECD detects thermal conductivity.
• C. FID detects masses; ECD detects color.
• D. FID detects ions; ECD detects neutral molecules.

Answer: (A)

The main idea is how two GC detectors work at a fundamental level and what they are most sensitive to. In a flame ionization detector, the organic compounds that elute from the column are burned in a hydrogen–air flame. The combustion creates ions, and the detector measures the resulting current. The signal is roughly proportional to the number of carbon atoms present, so FID is very responsive to most organic compounds in general. It is not selective for a particular class and won’t respond well to inorganic gases or noncombustible species. In an electron capture detector, a radioactive source generates electrons in the detector, and the carrier gas allows these electrons to interact with analyte molecules. Compounds that readily capture electrons—electronegative species, especially halogenated compounds—cause a drop in current, making ECD extremely sensitive and selective for those kinds of substances. The described statement reflects these principles and the distinct selectivities: FID detects ions produced by combustion of organic compounds, ECD detects electronegative species via electron capture, and ECD is highly selective for halogenated compounds. The other options pair detectors with incorrect detection principles (UV absorption, thermal conductivity, masses, color) or misstate what each detector senses, so they don’t fit.

The main idea is how two GC detectors work at a fundamental level and what they are most sensitive to.

In a flame ionization detector, the organic compounds that elute from the column are burned in a hydrogen–air flame. The combustion creates ions, and the detector measures the resulting current. The signal is roughly proportional to the number of carbon atoms present, so FID is very responsive to most organic compounds in general. It is not selective for a particular class and won’t respond well to inorganic gases or noncombustible species.

In an electron capture detector, a radioactive source generates electrons in the detector, and the carrier gas allows these electrons to interact with analyte molecules. Compounds that readily capture electrons—electronegative species, especially halogenated compounds—cause a drop in current, making ECD extremely sensitive and selective for those kinds of substances.

The described statement reflects these principles and the distinct selectivities: FID detects ions produced by combustion of organic compounds, ECD detects electronegative species via electron capture, and ECD is highly selective for halogenated compounds. The other options pair detectors with incorrect detection principles (UV absorption, thermal conductivity, masses, color) or misstate what each detector senses, so they don’t fit.