After the components of a mixture are separated using gas chromatography , they must be detected as they exit the GC column . The links listed below provide the details of some specific GC detectors. The thermal-conductivity (TCD) and flame-ionization (FID) detectors are the two most common detectors on commercial gas chromatographs. The requirements of a GC detector depends on the separation application. For example, one analysis might require a detector that is selective for chlorine-containing molecules, another analysis might require a detector that is non-destructive so that the analyte can be recovered for further spectroscopic analysis. Specific GC detectorsAtomic-emmision detector (AED)Chemiluminescence detectorElectron-capture detector (ECD)The ECD is as sensitive as the FID but has a limited dynamic range and finds its greatest application in analysis organic molecules that contain electronegative functional groups, such as halogens, phosphorous, and nitro groups. Flame-ionization detector (FID)The FID is extremely sensitive with a large dynamic range, its only disadvantage is that it destroys the sample. Flame-photometric detector (FPD)Mass spectrometer (MS)Mass spectrometers provide structural information to identify the analyte in a chromatographic peak. Nitrogen-phosphorus detector (NPD)A detector similar in design to an FID but with selectivity for compounds containing nitrogen and phosphorus. Photoionization detector (PID)Thermal conductivity detector (TCD)The TCD is not as sensitive as other dectectors but it is non-specific and non-destructive.