There are many great detectors for gas chromatography. “Great” in the sense of fast enough to monitor peaks in high-resolution GC separations without peak distortion. “Great” also as to high sensitivities (i.e. strong signals) and low noise, together resulting in low limits of detection (LODs). Achideving the latter is aided by the inert carrier gas, which gives rise to low backgrounds and low noise.
“Great” may also reflect the selectivity of the detector. A classification of common GC detectors according to their selectivity is shown in the figure below.
Some detectors are “great” because they are universal, i.e. they respond to nearly all analytes. Examples are the flame-ionization detector (FID) and the thermal-conductivity detector (TCD). The FID, based on ionization of the analytes in a tiny hydrogen-air flame, is especially attractive, because of the extremely low LODs that can be reached, its simplicity and robustness, and the near equal response factors for analytes with similar chemical structures.
Other detectors are “great” because they are highly selective or even specific for certain elements. Element-selective detectors show greatly increased sensitivity for analyte molecules that contain certain chemical elements. Examples include the nitrogen-phosphorous or thermionic detector (NPD), the flame-photometric detector (FPD; selective for sulphur or phosphorous), or the electron-capture detector (ECD; mainly selective for halogen elements). Element-specific detectors only respond to certain elements. Examples are sulphur-chemiluminescence and nitrogen-chemiluminescence detectors (SCD and NCD, respectively). Atomic-emission detectors (AED) can be tuned to a range of specific elements.
At the bottom of the figure are (molar-)mass-selective detectors, which can (nearly) simultaneously record masses of molecular ions or fragment ions in real time. Such combinations of GC and mass spectrometry (i.e. GC-MS) are treated in a different post.
For more information on GC detectors see Module 2.5
